Glibc build generates header files to define constants from special .sym
files. If a .sym file includes the same header file which it generates,
it leads to circular dependency which may lead to build hang on a
many-core machine. Define GEN_AS_CONST_HEADERS when generating header
files to avoid circular dependency.
<tcb-offsets.h> is needed for i686 and it isn't needed for x86-64 at
least since glibc 2.23.
Tested on i686 and x86-64.
[BZ #22792]
* Makerules ($(common-objpfx)%.h): Pass -DGEN_AS_CONST_HEADERS
to $(CC).
* sysdeps/unix/sysv/linux/i386/lowlevellock.h: Include
<tcb-offsets.h> only if GEN_AS_CONST_HEADERS isn't defined.
* sysdeps/unix/sysv/linux/x86_64/lowlevellock.h: Don't include
<tcb-offsets.h>.
The RISC-V Linux ABI doesn't define any libraries that go directly in
lib, instead they go into lib32/ilp32 or lib64/lp64. This casuse
make-link-multidir to fail when attempting to make library directories
when building a static libc on multilib RISC-V systems.
This patch uses scripts/mkinstalldirs to make the base directory of the
target symlink of make-link-multidir.
2018-01-06 Palmer Dabbelt <palmer@sifive.com>
* Makerules (make-link-multidir): Make directories before linking into
them.
When multi-lib GCC is used to build glibc, the search order of GCC driver
for crt*.o is -B*/`gcc -print-multi-directory`, the installed diretory,
-B*/. This patch adds multi-lib support to csu/Makefile so that
-B/glibc-build-directory/csu/ will pick up the newly built crt*.o.
Tested on x86-64 for i686 and x32.
[BZ #22362]
* Makerules (make-link-multidir): New.
* config.make.in (multidir): New.
* configure.ac (libc_cv_multidir): New. AC_SUBST.
* configure: Regenerated.
* csu/Makefile [$(multidir) != .](multilib-extra-objs): New.
[$(multidir) != .](extra-objs): Add $(multilib-extra-objs).
[$(multidir) != .]($(addprefix $(objpfx)$(multidir)/, $(install-lib))):
New target.
Since sofini.os terminates .eh_frame section, it should be placed last.
[BZ #22051]
* Makerules (build-module-helper-objlist): Filter out
$(elf-objpfx)sofini.os.
(build-shlib-objlist): Append $(elf-objpfx)sofini.os if it is
needed.
Some programs have more than one source files. These non-lib modules
should not be compiled with -DMODULE_NAME=libc. This patch puts these
non-lib modules in $(others-extras) and adds $(others-extras) to
all-nonlib.
[BZ #21864]
* Makerules (all-nonlib): Add $(others-extras).
* catgets/Makefile (others-extras): New.
* elf/Makefile (others-extras): Likewise.
* nss/Makefile (others-extras): Likewise.
__need_FOPEN_MAX wasn't being used anywhere. __need_IOV_MAX was more
complicated; the basic deal is that sys/uio.h wants to define a
constant named UIO_MAXIOV and bits/xopen_lim.h wants to define a
constant named IOV_MAX, with the same meaning. For no apparent reason
this was being handled via bits/stdio_lim.h -- stdio.h is NOT supposed
to define IOV_MAX -- and some mess in Makerules. Also, bits/uio.h on
Linux was being used as a dumping ground for extension functions.
So now we have bits/uio_lim.h, which defines __IOV_MAX.
bits/xopen_lim.h and sys/uio.h use that to define their respective
constants. We also now have bits/uio-ext.h, which is the official
Proper Home for extensions to sys/uio.h. bits/uio.h is removed, and
stdio_lim.h doesn't define IOV_MAX at all.
* bits/uio_lim.h, sysdeps/unix/sysv/linux/bits/uio_lim.h
* bits/uio-ext.h, sysdeps/unix/sysv/linux/bits/uio-ext.h: New file.
* bits/uio.h, sysdeps/unix/sysv/linux/bits/uio.h: Delete file.
* include/bits/xopen_lim.h: Use bits/uio_lim.h to get the value
for IOV_MAX.
* misc/Makefile: Install bits/uio-ext.h and bits/uio_lim.h.
Don't install bits/uio.h.
* misc/sys/uio.h: Don't include bits/uio.h. Do include
bits/types/struct_iovec.h and bits/uio_lim.h. Set UIO_MAXIOV
based on __IOV_MAX. Under __USE_GNU, also include bits/uio-ext.h.
* stdio-common/stdio_lim.h.in: Remove logic for __need_FOPEN_MAX
and __need_IOV_MAX. Don't define IOV_MAX at all.
* Makerules (stdio_lim.h): Remove logic for setting IOV_MAX.
* sysdeps/unix/sysv/linux/bits/fcntl-linux.h:
Include bits/types/struct_iovec.h, not bits/uio.h.
Use __ssize_t, not ssize_t, in function prototypes.
Don't use hard TAB for double space after period in comments.
<bits/std_abs.h> from GCC 7 will include /usr/include/stdlib.h from
"#include_next" (instead of stdlib/stdlib.h in the glibc source
directory), and this turns up as a make dependency. Also make a copy
of <bits/std_abs.h> to prevent it from including /usr/include/stdlib.h.
[BZ #21573]
* Makerules [$(c++-bits-std_abs-h) != ""] (before-compile): Add
$(common-objpfx)bits/std_abs.h.
[$(c++-bits-std_abs-h) != ""] ($(common-objpfx)bits/std_abs.h):
New target.
* config.make.in (c++-bits-std_abs-h): New.
* configure.ac (find_cxx_header): Use "\,$1," with sed.
(CXX_BITS_STD_ABS_H): New.
(AC_SUBST(CXX_BITS_STD_ABS_H)): Likewise.
* configure: Regenerated.
This patch makes the glibc build generate an additional header
ldbl-compat-choose.h that defines LONG_DOUBLE_COMPAT_CHOOSE_* macros
for each libc and libm symbol, which select one or the other of their
arguments based on whether the symbol was added before a change to
long double != double.
The effect of this is that it is then possible to define a macro
maybe_long_double_symbol that automatically acts as either
long_double_symbol or weak_alias depending on when the symbol being
defined was added. This can be used when building long double
functions from type-generic templates. Thus, with this patch ldbl-opt
no longer needs special long double implementations of each new libm
function added using such a template, and the existing such
implementations are removed.
This is a step towards being able more generally to use common macros
to create all the aliases needed for a libm function, so reducing the
amount of special-case code needed in ldbl-opt and ldbl-64-128, and
facilitating subsequently adding *f32 / *f64 / *f128 / *f32x / *f64x
aliases to existing functions (where the set of aliases that a
function should have may depend on the architecture in various ways).
Tested with build-many-glibcs.py. Except for on
powerpc64le-linux-gnu, installed stripped shared libraries are
unchanged by the patch. powerpc64le-linux-gnu is the unique
configuration which used ldbl-opt from the start rather than adding a
new long double choice after originally only having had long double =
double. The effect of the patch there is that various cases that
previously used long_double_symbol unconditionally now use weak_alias
instead, so .os files contain e.g. a symbol cabsl instead of
cabsl@@GLIBC_2.17. The final dynamic symbols and versions in the
resulting shared libraries are unchanged (ABI tests pass), as is the
disassembly of the shared libraries, but the differences in the .os
files still result in different .gnu_hash contents in libm.so; the
differences are of no significance and logically using weak_alias is
what's most appropriate in those cases.
* scripts/versions.awk: Generate ldbl-compat-choose.h.
* sysdeps/ieee754/ldbl-opt/math-type-macros-ldouble.h: Include
<ldbl-compat-choose.h>.
(maybe_long_double_symbol): New macro.
[!declare_mgen_alias] (declare_mgen_alias): Use
maybe_long_double_symbol.
* sysdeps/ieee754/ldbl-opt/s_canonicalizel.c: Remove.
* sysdeps/ieee754/ldbl-opt/s_fmaxmagl.c: Likewise.
* sysdeps/ieee754/ldbl-opt/s_fminmagl.c: Likewise.
* sysdeps/ieee754/ldbl-opt/s_nextdownl.c: Likewise.
* sysdeps/ieee754/ldbl-opt/w_llogbl.c: Likewise.
* Makerules [$(build-shared) = yes && !avoid-generated]
(before-compile): Add $(common-objpfx)ldbl-compat-choose.h.
[$(build-shared) = yes && !avoid-generated]
($(common-objpfx)ldbl-compat-choose.h): New target.
This patch arranges for the glibc build to generate a header
first-versions.h that defines macros for the earliest symbol version
in which each public symbol (GLIBC_[0-9]* symbol version, name only
uses C identifier characters) is available.
This is used in sysdeps/ieee754/ldbl-opt/math-type-macros-double.h to
replace the manually defined LDOUBLE_*_libm_version macros for various
functions defined using type-generic templates, the purpose of which
is to use in LONG_DOUBLE_COMPAT tests "was this function originally
added before glibc supported long double != double on this platform?".
As discussed in
<https://sourceware.org/ml/libc-alpha/2016-12/msg00246.html>, I expect
this to be useful more generally in reducing the amount of
special-case code needed in ldbl-opt and ldbl-64-128.
Tested with build-many-glibcs.py that installed stripped shared
libraries are unchanged by this patch.
* scripts/versions.awk: Generate first-versions.h.
* sysdeps/ieee754/ldbl-opt/math-type-macros-double.h: Include
<first-versions.h>.
(LDOUBLE_cabsl_libm_version): Remove macro.
(LDOUBLE_cargl_libm_version): Likewise.
(LDOUBLE_cimagl_libm_version): Likewise.
(LDOUBLE_conjl_libm_version): Likewise.
(LDOUBLE_creall_libm_version): Likewise.
(LDOUBLE_cacosl_libm_version): Likewise.
(LDOUBLE_cacoshl_libm_version): Likewise.
(LDOUBLE_ccosl_libm_version): Likewise.
(LDOUBLE_ccoshl_libm_version): Likewise.
(LDOUBLE_casinl_libm_version): Likewise.
(LDOUBLE_csinl_libm_version): Likewise.
(LDOUBLE_casinhl_libm_version): Likewise.
(LDOUBLE_csinhl_libm_version): Likewise.
(LDOUBLE_catanl_libm_version): Likewise.
(LDOUBLE_catanhl_libm_version): Likewise.
(LDOUBLE_ctanl_libm_version): Likewise.
(LDOUBLE_ctanhl_libm_version): Likewise.
(LDOUBLE_cexpl_libm_version): Likewise.
(LDOUBLE_clogl_libm_version): Likewise.
(LDOUBLE_cprojl_libm_version): Likewise.
(LDOUBLE_csqrtl_libm_version): Likewise.
(LDOUBLE_cpowl_libm_version): Likewise.
(LDOUBLE_clog10l_libm_version): Likewise.
(LDOUBLE___clog10l_libm_version): Likewise.
(LDOUBLE_fdiml_libm_version): Likewise.
(LDOUBLE_fmaxl_libm_version): Likewise.
(LDOUBLE_fminl_libm_version): Likewise.
(LDOUBLE_ilogbl_libm_version): Likewise.
(LDOUBLE_nanl_libm_version): Likewise.
[!M_LIBM_NEED_COMPAT] (M_LIBM_NEED_COMPAT): Use
FIRST_VERSION_libm_* macros.
[!declare_mgen_libm_compat] (declare_mgen_libm_compat): Likewise.
* Makerules [$(build-shared) = yes && !avoid-generated]
(before-compile): Add $(common-objpfx)first-versions.h.
[$(build-shared) = yes && !avoid-generated]
($(common-objpfx)first-versions.h): New target.
($(common-objpfx)sysd-versions): Depend on and change to rule for
building $(common-objpfx)versions.stmp.
This patch adds a new build module called 'testsuite'.
IS_IN (testsuite) implies _ISOMAC, as do IS_IN_build and __cplusplus
(which means several ad-hoc tests for __cplusplus can go away).
libc-symbols.h now suppresses almost all of *itself* when _ISOMAC is
defined; in particular, _ISOMAC mode does not get config.h
automatically anymore.
There are still quite a few tests that need to see internal gunk of
one variety or another. For them, we now have 'tests-internal' and
'test-internal-extras'; files in this category will still be compiled
with MODULE_NAME=nonlib, and everything proceeds as it always has.
The bulk of this patch is moving tests from 'tests' to
'tests-internal'. There is also 'tests-static-internal', which has
the same effect on files in 'tests-static', and 'modules-names-tests',
which has the *inverse* effect on files in 'modules-names' (it's
inverted because most of the things in modules-names are *not* tests).
For both of these, the file must appear in *both* the new variable and
the old one.
There is also now a special case for when libc-symbols.h is included
without MODULE_NAME being defined at all. (This happens during the
creation of libc-modules.h, and also when preprocessing Versions
files.) When this happens, IS_IN is set to be always false and
_ISOMAC is *not* defined, which was the status quo, but now it's
explicit.
The remaining changes to C source files in this patch seemed likely to
cause problems in the absence of the main change. They should be
relatively self-explanatory. In a few cases I duplicated a definition
from an internal header rather than move the test to tests-internal;
this was a judgement call each time and I'm happy to change those
however reviewers feel is more appropriate.
* Makerules: New subdir configuration variables 'tests-internal'
and 'test-internal-extras'. Test files in these categories will
still be compiled with MODULE_NAME=nonlib. Test files in the
existing categories (tests, xtests, test-srcs, test-extras) are
now compiled with MODULE_NAME=testsuite.
New subdir configuration variable 'modules-names-tests'. Files
which are in both 'modules-names' and 'modules-names-tests' will
be compiled with MODULE_NAME=testsuite instead of
MODULE_NAME=extramodules.
(gen-as-const-headers): Move to tests-internal.
(do-tests-clean, common-mostlyclean): Support tests-internal.
* Makeconfig (built-modules): Add testsuite.
* Makefile: Change libof-check-installed-headers-c and
libof-check-installed-headers-cxx to 'testsuite'.
* Rules: Likewise. Support tests-internal.
* benchtests/strcoll-inputs/filelist#en_US.UTF-8:
Remove extra-modules.mk.
* config.h.in: Don't check for __OPTIMIZE__ or __FAST_MATH__ here.
* include/libc-symbols.h: Move definitions of _GNU_SOURCE,
PASTE_NAME, PASTE_NAME1, IN_MODULE, IS_IN, and IS_IN_LIB to the
very top of the file and rationalize their order.
If MODULE_NAME is not defined at all, define IS_IN to always be
false, and don't define _ISOMAC.
If any of IS_IN (testsuite), IS_IN_build, or __cplusplus are
true, define _ISOMAC and suppress everything else in this file,
starting with the inclusion of config.h.
Do check for inappropriate definitions of __OPTIMIZE__ and
__FAST_MATH__ here, but only if _ISOMAC is not defined.
Correct some out-of-date commentary.
* include/math.h: If _ISOMAC is defined, undefine NO_LONG_DOUBLE
and _Mlong_double_ before including math.h.
* include/string.h: If _ISOMAC is defined, don't expose
_STRING_ARCH_unaligned. Move a comment to a more appropriate
location.
* include/errno.h, include/stdio.h, include/stdlib.h, include/string.h
* include/time.h, include/unistd.h, include/wchar.h: No need to
check __cplusplus nor use __BEGIN_DECLS/__END_DECLS.
* misc/sys/cdefs.h (__NTHNL): New macro.
* sysdeps/m68k/m680x0/fpu/bits/mathinline.h
(__m81_defun): Use __NTHNL to avoid errors with GCC 6.
* elf/tst-env-setuid-tunables.c: Include config.h with _LIBC
defined, for HAVE_TUNABLES.
* inet/tst-checks-posix.c: No need to define _ISOMAC.
* intl/tst-gettext2.c: Provide own definition of N_.
* math/test-signgam-finite-c99.c: No need to define _ISOMAC.
* math/test-signgam-main.c: No need to define _ISOMAC.
* stdlib/tst-strtod.c: Convert to test-driver. Split locale_test to...
* stdlib/tst-strtod1i.c: ...this new file.
* stdlib/tst-strtod5.c: Convert to test-driver and add copyright notice.
Split tests of __strtod_internal to...
* stdlib/tst-strtod5i.c: ...this new file.
* string/test-string.h: Include stdint.h. Duplicate definition of
inhibit_loop_to_libcall here (from libc-symbols.h).
* string/test-strstr.c: Provide dummy definition of
libc_hidden_builtin_def when including strstr.c.
* sysdeps/ia64/fpu/libm-symbols.h: Suppress entire file in _ISOMAC
mode; no need to test __STRICT_ANSI__ nor __cplusplus as well.
* sysdeps/x86_64/fpu/math-tests-arch.h: Include cpu-features.h.
Don't include init-arch.h.
* sysdeps/x86_64/multiarch/test-multiarch.h: Include cpu-features.h.
Don't include init-arch.h.
* elf/Makefile: Move tst-ptrguard1-static, tst-stackguard1-static,
tst-tls1-static, tst-tls2-static, tst-tls3-static, loadtest,
unload, unload2, circleload1, neededtest, neededtest2,
neededtest3, neededtest4, tst-tls1, tst-tls2, tst-tls3,
tst-tls6, tst-tls7, tst-tls8, tst-dlmopen2, tst-ptrguard1,
tst-stackguard1, tst-_dl_addr_inside_object, and all of the
ifunc tests to tests-internal.
Don't add $(modules-names) to test-extras.
* inet/Makefile: Move tst-inet6_scopeid_pton to tests-internal.
Add tst-deadline to tests-static-internal.
* malloc/Makefile: Move tst-mallocstate and tst-scratch_buffer to
tests-internal.
* misc/Makefile: Move tst-atomic and tst-atomic-long to tests-internal.
* nptl/Makefile: Move tst-typesizes, tst-rwlock19, tst-sem11,
tst-sem12, tst-sem13, tst-barrier5, tst-signal7, tst-tls3,
tst-tls3-malloc, tst-tls5, tst-stackguard1, tst-sem11-static,
tst-sem12-static, and tst-stackguard1-static to tests-internal.
Link tests-internal with libpthread also.
Don't add $(modules-names) to test-extras.
* nss/Makefile: Move tst-field to tests-internal.
* posix/Makefile: Move bug-regex5, bug-regex20, bug-regex33,
tst-rfc3484, tst-rfc3484-2, and tst-rfc3484-3 to tests-internal.
* stdlib/Makefile: Move tst-strtod1i, tst-strtod3, tst-strtod4,
tst-strtod5i, tst-tls-atexit, and tst-tls-atexit-nodelete to
tests-internal.
* sunrpc/Makefile: Move tst-svc_register to tests-internal.
* sysdeps/powerpc/Makefile: Move test-get_hwcap and
test-get_hwcap-static to tests-internal.
* sysdeps/unix/sysv/linux/Makefile: Move tst-setgetname to
tests-internal.
* sysdeps/x86_64/fpu/Makefile: Add all libmvec test modules to
modules-names-tests.
cppflags-iterator.mk no longer has anything to do with CPPFLAGS; all
it does is set libof-$(foo) for a list of files. extra-modules.mk
does the same thing, but with a different input variable, and doesn't
let the caller control the module. Therefore, this patch gives
cppflags-iterator.mk a better name, removes extra-modules.mk, and
updates all uses of both.
* extra-modules.mk: Delete file.
* cppflags-iterator.mk: Rename to ...
* libof-iterator.mk: ...this. Adjust comments.
* Makerules, extra-lib.mk, benchtests/Makefile, elf/Makefile
* elf/rtld-Rules, iconv/Makefile, locale/Makefile, malloc/Makefile
* nscd/Makefile, sunrpc/Makefile, sysdeps/s390/Makefile:
Use libof-iterator.mk instead of cppflags-iterator.mk or
extra-modules.mk.
* benchtests/strcoll-inputs/filelist#en_US.UTF-8: Remove
extra-modules.mk and cppflags-iterator.mk, add libof-iterator.mk.
This patch adds pretty printers for the following NPTL types:
- pthread_mutex_t
- pthread_mutexattr_t
- pthread_cond_t
- pthread_condattr_t
- pthread_rwlock_t
- pthread_rwlockattr_t
To load the pretty printers into your gdb session, do the following:
python
import sys
sys.path.insert(0, '/path/to/glibc/build/nptl/pretty-printers')
end
source /path/to/glibc/source/pretty-printers/nptl-printers.py
You can check which printers are registered and enabled by issuing the
'info pretty-printer' gdb command. Printers should trigger automatically when
trying to print a variable of one of the types mentioned above.
The printers are architecture-independent, and were tested on an AMD64 running
Ubuntu 14.04 and an x86 VM running Fedora 24.
In order to work, the printers need to know the values of various flags that
are scattered throughout pthread.h and pthreadP.h as enums and #defines. Since
replicating these constants in the printers file itself would create a
maintenance burden, I wrote a script called gen-py-const.awk that Makerules uses
to extract the constants. This script is pretty much the same as gen-as-const.awk,
except it doesn't cast the constant values to 'long' and is thorougly documented.
The constants need only to be enumerated in a .pysym file, which is then referenced
by a Make variable called gen-py-const-headers.
As for the install directory, I discussed this with Mike Frysinger and Siddhesh
Poyarekar, and we agreed that it can be handled in a separate patch, and shouldn't
block merging of this one.
In addition, I've written a series of test cases for the pretty printers.
Each lock type (mutex, condvar and rwlock) has two test programs, one for itself
and other for its related 'attributes' object. Each test program in turn has a
PExpect-based Python script that drives gdb and compares its output to the
expected printer's. The tests run on the glibc host, which is assumed to have
both gdb and PExpect; if either is absent the tests will fail with code 77
(UNSUPPORTED). For cross-testing you should use cross-test-ssh.sh as test-wrapper.
I've tested the printers on both native builds and a cross build using a Beaglebone
Black running Debian, with the build system's filesystem shared with the board
through NFS.
Finally, I've written a README that explains all this and more.
* INSTALL: Regenerated.
* Makeconfig: Add comments and whitespace to make the control flow
clearer.
(+link-printers-tests, +link-pie-printers-tests, CFLAGS-printers-tests,
installed-rtld-LDFLAGS, built-rtld-LDFLAGS, link-libc-rpath,
link-libc-tests-after-rpath-link, link-libc-printers-tests): New.
(rtld-LDFLAGS, rtld-tests-LDFLAGS, link-libc-tests-rpath-link,
link-libc-tests): Use the new variables as required.
* Makerules ($(py-const)): New rule.
generated: Add $(py-const).
* README.pretty-printers: New file.
* Rules (tests-printers-programs, tests-printers-out, py-env): New.
(others): Depend on $(py-const).
(tests): Depend on $(tests-printers-programs) or $(tests-printers-out),
as required. Pass $(tests-printers) to merge-test-results.sh.
* manual/install.texi: Add requirements for testing the pretty printers.
* nptl/Makefile (gen-py-const-headers, pretty-printers, tests-printers,
CFLAGS-test-mutexattr-printers.c CFLAGS-test-mutex-printers.c,
CFLAGS-test-condattr-printers.c, CFLAGS-test-cond-printers.c,
CFLAGS-test-rwlockattr-printers.c CFLAGS-test-rwlock-printers.c,
tests-printers-libs): Define.
* nptl/nptl-printers.py: New file.
* nptl/nptl_lock_constants.pysym: Likewise.
* nptl/test-cond-printers.c: Likewise.
* nptl/test-cond-printers.py: Likewise.
* nptl/test-condattr-printers.c: Likewise.
* nptl/test-condattr-printers.py: Likewise.
* nptl/test-mutex-printers.c: Likewise.
* nptl/test-mutex-printers.py: Likewise.
* nptl/test-mutexattr-printers.c: Likewise.
* nptl/test-mutexattr-printers.py: Likewise.
* nptl/test-rwlock-printers.c: Likewise.
* nptl/test-rwlock-printers.py: Likewise.
* nptl/test-rwlockattr-printers.c: Likewise.
* nptl/test-rwlockattr-printers.py: Likewise.
* scripts/gen-py-const.awk: Likewise.
* scripts/test_printers_common.py: Likewise.
* scripts/test_printers_exceptions.py: Likewise.
This was used by --enable-omitfp, and the bulk of it was removed in this
commit:
commit bdeba1354b
Author: Ulrich Drepper <drepper@gmail.com>
Date: Sat Jan 7 11:29:31 2012 -0500
Remove --enable-omitfp support
This reverts commit 62ce266b0b.
The change is not mature enough because it needs the following fixes:
1. Redirect test output to a file like other tests
2. Eliminate the need to use a .gdbinit because distributions will
break without it. I should have caught that but I was in too much
of a hurry to get the patch in :/
3. Feature checking during configure to determine things like minimum
required gdb version, python-pexpect version, etc. to make sure
that tests work correctly.
This patch adds pretty printers for the following NPTL types:
- pthread_mutex_t
- pthread_mutexattr_t
- pthread_cond_t
- pthread_condattr_t
- pthread_rwlock_t
- pthread_rwlockattr_t
To load the pretty printers into your gdb session, do the following:
python
import sys
sys.path.insert(0, '/path/to/glibc/build/nptl/pretty-printers')
end
source /path/to/glibc/source/pretty-printers/nptl-printers.py
You can check which printers are registered and enabled by issuing the
'info pretty-printer' gdb command. Printers should trigger automatically when
trying to print a variable of one of the types mentioned above.
The printers are architecture-independent, and were manually tested on both
the gdb CLI and Eclipse CDT.
In order to work, the printers need to know the values of various flags that
are scattered throughout pthread.h and pthreadP.h as enums and #defines. Since
replicating these constants in the printers file itself would create a
maintenance burden, I wrote a script called gen-py-const.awk that Makerules uses
to extract the constants. This script is pretty much the same as gen-as-const.awk,
except it doesn't cast the constant values to 'long' and is thorougly documented.
The constants need only to be enumerated in a .pysym file, which is then referenced
by a Make variable called gen-py-const-headers.
As for the install directory, I discussed this with Mike Frysinger and Siddhesh
Poyarekar, and we agreed that it can be handled in a separate patch, and it shouldn't
block merging of this one.
In addition, I've written a series of test cases for the pretty printers.
Each lock type (mutex, condvar and rwlock) has two test programs, one for itself
and other for its related 'attributes' object. Each test program in turn has a
PExpect-based Python script that drives gdb and compares its output to the
expected printer's. The tests run on the glibc host, which is assumed to have
both gdb and PExpect; if either is absent the tests will fail with code 77
(UNSUPPORTED). For cross-testing you should use cross-test-ssh.sh as test-wrapper.
I've tested the printers on both a native build and a cross build using a Beaglebone
Black, with the build system's filesystem shared with the board through NFS.
Finally, I've written a README that explains all this and more.
Hopefully this should be good to go in now. Thanks.
ChangeLog:
2016-07-04 Martin Galvan <martin.galvan@tallertechnologies.com>
* Makeconfig (build-hardcoded-path-in-tests): Set to 'yes' for shared builds
if tests-need-hardcoded-path is defined.
(all-subdirs): Add pretty-printers.
* Makerules ($(py-const)): New rule.
* Rules (others): Add $(py-const), if defined.
* nptl/Makefile (gen-py-const-headers): Define.
* nptl/nptl-printers.py: New file.
* nptl/nptl_lock_constants.pysym: Likewise.
* pretty-printers/Makefile: Likewise.
* pretty-printers/README: Likewise.
* pretty-printers/test-condvar-attributes.c: Likewise.
* pretty-printers/test-condvar-attributes.p: Likewise.
* pretty-printers/test-condvar-printer.c: Likewise.
* pretty-printers/test-condvar-printer.py: Likewise.
* pretty-printers/test-mutex-attributes.c: Likewise.
* pretty-printers/test-mutex-attributes.py: Likewise.
* pretty-printers/test-mutex-printer.c: Likewise.
* pretty-printers/test-mutex-printer.py: Likewise.
* pretty-printers/test-rwlock-attributes.c: Likewise.
* pretty-printers/test-rwlock-attributes.py: Likewise.
* pretty-printers/test-rwlock-printer.c: Likewise.
* pretty-printers/test-rwlock-printer.py: Likewise.
* pretty-printers/test_common.py: Likewise.
* scripts/gen-py-const.awk: Likewise.
If C++ headers <cstdlib> or <cmath> are used, GCC 6 will include
/usr/include/stdlib.h or /usr/include/math.h from "#include_next"
(instead of stdlib/stdlib.h or math/math.h in the glibc source
directory), and this turns up as a make dependency. An implicit
rule will kick in and make will try to install stdlib/stdlib.h or
math/math.h as /usr/include/stdlib.h or /usr/include/math.h because
the target is out of date. We make a copy of <cstdlib> and <cmath>
in the glibc build directory so that stdlib/stdlib.h and math/math.h
will be used instead of /usr/include/stdlib.h and /usr/include/math.h.
[BZ #20314]
* Makeconfig (CXXFLAGS): Prepend -I$(common-objpfx).
* Makerules (before-compile): Add $(common-objpfx)cstdlib and
$(common-objpfx)cmath.
($(common-objpfx)cstdlib): New target.
($(common-objpfx)cmath): Likewise.
This commit puts all libio vtables in a dedicated, read-only ELF
section, so that they are consecutive in memory. Before any indirect
jump, the vtable pointer is checked against the section boundaries,
and the process is terminated if the vtable pointer does not fall into
the special ELF section.
To enable backwards compatibility, a special flag variable
(_IO_accept_foreign_vtables), protected by the pointer guard, avoids
process termination if libio stream object constructor functions have
been called earlier. Such constructor functions are called by the GCC
2.95 libstdc++ library, and this mechanism ensures compatibility with
old binaries. Existing callers inside glibc of these functions are
adjusted to call the original functions, not the wrappers which enable
vtable compatiblity.
The compatibility mechanism is used to enable passing FILE * objects
across a static dlopen boundary, too.
There is a configure test for -static-libgcc. GCC added this option
in version 3.0, so this test is obsolete; this patch removes it.
Tested for x86_64 and x86 (testsuite, and that installed shared
libraries are unchanged by the patch).
* configure.ac (libc_cv_gcc_static_libgcc): Remove configure test.
* configure: Regenerated.
* config.make.in (static-libgcc): Remove variable.
* Makerules (build-shlib-helper): Use -static-libgcc instead of
$(static-libgcc).
(build-module-helper): Likewise.
a non-standard directory specified by the prefix make variable
fails with an error. Since this is an unsupported use case,
this change makes make install fail early and with a descriptive
error message when either the prefix or the exec_prefix make
variable is overridden on the command line.
Make runtime-linker.h available outside $(elf-objpfx) by moving
the file to $(common-objpfx) and the rules for it to Makerules.
Tested for x86_64 and x86 (testsuite, and that no compiled code
changed by the patch).
* Makeconfig (+interp): Remove unused variable.
* elf/Makefile ($(objpfx)interp.os): Define for [$(build-shared) = yes]
only. Depend on $(common-objpfx)runtime-linker.h instead of
$(elf-objpfx)runtime-linker.h.
($(elf-objpfx)runtime-linker.h): Rename to
$(common-objpfx)runtime-linker.h and move ...
* Makerules [$(build-shared) = yes]: ... here.
* elf/interp.c: Include <runtime-linker.h> instead of
<elf/runtime-linker.h>.
The current scheme to identify which module a translation unit is
built in depends on defining multiple macros IS_IN_* and also defining
NOT_IN_libc if we're building a non-libc module. In addition, there
is an IN_LIB macro that does effectively the same thing, but for
different modules (notably the systemtap probes). This macro scheme
unifies both ideas to use just one macro IN_MODULE and assign it a
value depending on the module it is being built into. If the module
is not defined, it defaults to MODULE_libc.
Patches that follow will replace uses of IS_IN_* variables with the
IS_IN() macro. libc-symbols.h has been converted already to give an
example of how such a transition will look.
Verified that there are no relevant binary changes. One source change
that will crop up repeatedly is that of nscd_stat, since it uses the
build timestamp as a constant in its logic.
* Makeconfig (in-module): Get value of libof set for the
translation unit.
(CPPFLAGS): Use $(in-module).
* Makerules: Don't suffix routine names for nonlib.
* include/libc-modules.h: New file.
* include/libc-symbols.h: Include libc-modules.h
(IS_IN): New macro to replace IS_IN_* macros.
* elf/Makefile: Set libof-* for each routine.
* elf/rtld-Rules: Likewise.
* extra-modules.mk: Likewise.
* iconv/Makefile: Likewise.
* iconvdata/Makefile: Likewise.
* locale/Makefile: Likewise.
* malloc/Makefile: Likewise.
* nss/Makefile: Likewise.
* sysdeps/gnu/Makefile: Likewise.
* sysdeps/ieee754/ldbl-opt/Makefile: Likewise.
* sysdeps/unix/sysv/linux/Makefile: Likewise.
* sysdeps/s390/s390-64/Makefile: Likewise.
* nscd/Makefile: Set libof-* for each routine. Set CFLAGS and
CPPFLAGS for nscd instead of nonlib.
This patch eliminates the mixture of SONAME information in
shlib-versions files and SONAME information used to generate
gnu/lib-names.h in makefiles, with the information in the makefiles
being removed so all this information comes from the shlib-versions
files.
So that gnu/lib-names.h supports multiple ABIs, it is changed to be
generated on the same basis as gnu/stubs.h: when there are multiple
ABIs, gnu/lib-names.h is a wrapper header (the same header installed
whatever ABI is being built) and separate headers such as
gnu/lib-names-64.h contain the substantive contents (only one such
header being installed by any glibc build).
The rules for building gnu/lib-names.h were moved from Makeconfig to
Makerules because they need to come after sysdeps makefiles are
included (now that "ifndef abi-variants" is a toplevel conditional on
the rules rather than $(abi-variants) being evaluated later inside the
commands for a rule).
Tested for x86_64 and x86 that the installed shared libraries are
unchanged by this patch, and examined the installed gnu/lib-names*.h
headers by hand. Also tested the case of a single ABI (where there is
just a single header installed, again like stubs.h) by hacking
abi-variants to empty for x86_64.
[BZ #14171]
* Makeconfig [$(build-shared) = yes]
($(common-objpfx)soversions.mk): Don't handle SONAMEs specified in
makefiles.
[$(build-shared) = yes && $(soversions.mk-done) = t]
($(common-objpfx)gnu/lib-names.h): Remove rule.
[$(build-shared) = yes && $(soversions.mk-done) = t]
($(common-objpfx)gnu/lib-names.stmp): Likewise. Split and moved
to Makerules.
[$(build-shared) = yes && $(soversions.mk-done) = t]
(before-compile): Don't append $(common-objpfx)gnu/lib-names.h
here.
[$(build-shared) = yes && $(soversions.mk-done) = t]
(common-generated): Don't append gnu/lib-names.h and
gnu/lib-names.stmp here.
* Makerules [$(build-shared) = yes && $(soversions.mk-done) = t]
(lib-names-h-abi): New variable.
[$(build-shared) = yes && $(soversions.mk-done) = t]
(lib-names-stmp-abi): Likewise.
[$(build-shared) = yes && $(soversions.mk-done) = t &&
abi-variants] (before-compile): Append
$(common-objpfx)$(lib-names-h-abi).
[$(build-shared) = yes && $(soversions.mk-done) = t &&
abi-variants] (common-generated): Append gnu/lib-names.h.
[$(build-shared) = yes && $(soversions.mk-done) = t &&
abi-variants] (install-others-nosubdir): Depend on
$(inst_includedir)/$(lib-names-h-abi).
[$(build-shared) = yes && $(soversions.mk-done) = t &&
abi-variants] ($(common-objpfx)gnu/lib-names.h): New rule.
[$(build-shared) = yes && $(soversions.mk-done) = t]
($(common-objpfx)$(lib-names-h-abi)): New rule.
[$(build-shared) = yes && $(soversions.mk-done) = t]
($(common-objpfx)$(lib-names-stmp-abi)): Likewise.
[$(build-shared) = yes && $(soversions.mk-done) = t]
(common-generated): Append $(lib-names-h-abi) and
$(lib-names-stmp-abi).
* scripts/lib-names.awk: Do not handle multi being set.
* sysdeps/unix/sysv/linux/aarch64/Makefile (abi-lp64-ld-soname):
Remove variable.
(abi-lp64_be-ld-soname): Likewise.
* sysdeps/unix/sysv/linux/arm/Makefile (abi-soft-ld-soname):
Likewise.
(abi-hard-ld-soname): Likewise.
* sysdeps/unix/sysv/linux/i386/shlib-versions: New file.
* sysdeps/unix/sysv/linux/mips/Makefile (abi-o32_soft-ld-soname):
Remove variable.
(abi-o32_hard-ld-soname): Likewise.
(abi-o32_soft_2008-ld-soname): Likewise.
(abi-o32_hard_2008-ld-soname): Likewise.
(abi-n32_soft-ld-soname): Likewise.
(abi-n32_hard-ld-soname): Likewise.
(abi-n32_soft_2008-ld-soname): Likewise.
(abi-n32_hard_2008-ld-soname): Likewise.
(abi-n64_soft-ld-soname): Likewise.
(abi-n64_hard-ld-soname): Likewise.
(abi-n64_soft_2008-ld-soname): Likewise.
(abi-n64_hard_2008-ld-soname): Likewise.
* sysdeps/unix/sysv/linux/powerpc/Makefile (abi-64-v1-ld-soname):
Likewise.
(abi-64-v2-ld-soname): Likewise.
* sysdeps/unix/sysv/linux/powerpc/powerpc64/shlib-versions: Add
ld.so entries.
* sysdeps/unix/sysv/linux/s390/Makefile (abi-64-ld-soname): Remove
variable.
* sysdeps/unix/sysv/linux/s390/s390-64/shlib-versions: Add ld.so
entry.
* sysdeps/unix/sysv/linux/x86/Makefile (abi-32-ld-soname): Remove
variable.
(abi-64-ld-soname): Likewise.
(abi-x32-ld-soname): Likewise.
* sysdeps/unix/sysv/linux/x86_64/64/shlib-versions: Add ld.so
entry.
* sysdeps/unix/sysv/linux/x86_64/x32/shlib-versions: Likewise.
This patch removes the --enable-oldest-abi configure option, which has
long been bitrotten (as reported in bug 6652). The principle of
removing this option was agreed in the thread starting at
<https://sourceware.org/ml/libc-alpha/2013-07/msg00174.html>.
Tested for x86_64 and x86 that the installed shared libraries other
than libc.so are unchanged by this patch and that libc.so disassembly
and symbol versions are unchanged (debug info changes because of
changed line numbers in csu/version.c).
[BZ #6652]
* Makeconfig (soversions-default-setname): Remove variable.
($(common-objpfx)soversions.i): Don't pass default_setname to
soversions.awk.
* Makerules ($(common-objpfx)abi-versions.h): Don't pass
oldest_abi to abi-versions.awk.
* config.h.in (GLIBC_OLDEST_ABI): Remove macro undefine.
* config.make.in (oldest-abi): Remove variable.
* configure.ac (--enable-oldest-abi): Remove configure option.
* configure: Regenerated.
* csu/version.c (banner) [GLIBC_OLDEST_ABI]: Remove conditional
text.
* scripts/abi-versions.awk: Do not handle oldest_abi variable.
* scripts/soversions.awk: Do not handle default_setname variable.
* sysdeps/mach/hurd/configure.ac: Do not handle oldest_abi
variable.
* sysdeps/mach/hurd/configure: Regenerated.
* sysdeps/unix/sysv/linux/configure.ac: Do not handle oldest_abi
variable.
* sysdeps/unix/sysv/linux/configure: Regenerated.
Barring libc.so and libdl.so, none of the libraries have any entry
points, so it is pointless to add a .interp section for them. The
libdl.so entry point (in dlfcn/eval.c) is also defunct, so remove that
file as well.
Build tested for x86_64, ppc64 and s390x. I have not moved
CFLAGS-interp.c to CPPFLAGS-interp.c isnce I'll be removing it
completely in a follow-up patch.
Siddhesh
* Makerules (lib%.so): Don't include $(+interp) in
prerequisites.
* elf/Makefile (CFLAGS-interp.c): Don't define NOT_IN_libc.
* dlfcn/eval.c: Remove file.
As previously noted
<https://sourceware.org/ml/libc-alpha/2013-05/msg00696.html>,
$(elf-objpfx) and $(elfobjdir) are redundant and should be
consolidated. This patch consolidates on $(elf-objpfx) (for
consistency with $(csu-objpfx)), also changing direct uses of
$(common-objpfx)elf/ to use $(elf-objpfx).
Tested x86_64, including that installed shared libraries are unchanged
by the patch.
* Makeconfig [$(build-hardcoded-path-in-tests) = yes]
(rtld-tests-LDFLAGS): Use $(elf-objpfx) instead of
$(common-objpfx)elf/.
(link-libc-before-gnulib): Likewise.
(elfobjdir): Remove variable.
* Makefile (install): Use $(elf-objpfx) instead of
$(common-objpfx)elf/.
* Makerules (link-libc-args): Use $(elf-objpfx) instead of
$(elfobjdir)/.
(link-libc-deps): Likewise.
($(common-objpfx)libc.so): Likewise.
($(common-objpfx)linkobj/libc.so): Likewise.
[$(cross-compiling) = no] (symbolic-link-prog): Use $(elf-objpfx)
instead of $(common-objpfx)elf/.
(symbolic-link-list): Likewise.
* iconvdata/Makefile ($(inst_gconvdir)/gconv-modules)
[$(cross-compiling) = no]: Likewise.
* sysdeps/arm/Makefile (gnulib-arch): Use $(elf-objpfx) instead of
$(elfobjdir)/.
(static-gnulib-arch): Likewise.
* sysdeps/s390/s390-64/Makefile ($(inst_gconvdir)/gconv-modules)
[$(cross-compiling) = no]: Use $(elf-objpfx) instead of
$(common-objpfx)elf/.
localedata/ChangeLog:
* Makefile (LOCALEDEF): Use $(elf-objpfx) instead of
$(common-objpfx)elf/.
This patch is a revised and updated version of
<https://sourceware.org/ml/libc-alpha/2014-01/msg00196.html>.
In order to generate overall summaries of the results of all tests in
the glibc testsuite, we need to identify and concatenate the files
with the results of individual tests.
Tomas Dohnalek's patch used $(common-objpfx)*/*.test-result for this.
However, the normal glibc approach is explicit enumeration of the
expected set of files with a given property, rather than all files
matching some pattern like that. Furthermore, we would like to be
able to mark tests as UNRESOLVED if the file with their results is for
some reason missing, and in future we would like to be able to mark
tests as UNSUPPORTED if they are disabled for a particular
configuration (rather than simply having them missing from the list of
tests as at present). Such handling of tests that were not run or did
not record results requires an explicit enumeration of tests.
For the tests following the default makefile rules, $(tests) (and
$(xtests)) provides such an enumeration. Others, however, are added
directly as dependencies of the "tests" and "xtests" makefile
targets. This patch changes the makefiles to put them in variables
tests-special and xtests-special, with appropriate dependencies on the
tests listed there then being added centrally.
Those variables are used in Rules and so need to be set before Rules
is included in a subdirectory makefile, which is often earlier in the
makefile than the dependencies were present before. We previously
discussed the question of where to include Rules; see the question at
<https://sourceware.org/ml/libc-alpha/2012-11/msg00798.html>, and a
discussion in
<https://sourceware.org/ml/libc-alpha/2013-01/msg00337.html> of why
Rules is included early rather than late in subdirectory makefiles.
It was necessary to avoid an indirection through the check-abi target
and get the check-abi-* targets for individual libraries into the
tests-special variable. The intl/ test $(objpfx)tst-gettext.out,
previously built only because of dependencies from other tests, was
also added to tests-special for the same reason.
The entries in tests-special are the full makefile targets, complete
with $(objpfx) and .out. If a future change causes tests to be named
consistently with a .out suffix, this can be changed to include just
the path relative to $(objpfx), without .out.
Tested x86_64, including that the same set of files is generated in
the build directory by a build and testsuite run both before and after
the patch (except for changes to the
elf/tst-null-argv.debug.out.<number> file name), and a build with
run-built-tests=no to verify there aren't any more obvious instances
of the issue Marcus Shawcroft reported with a previous version in
<https://sourceware.org/ml/libc-alpha/2014-01/msg00462.html>.
* Makefile (tests): Change dependencies to ....
(tests-special): ... additions to this variable.
(tests): Depend on $(tests-special).
* Makerules (check-abi-list): New variable.
(check-abi): Depend on $(check-abi-list).
[$(subdir) = elf] (tests-special): Add
$(objpfx)check-abi-libc.out.
[$(build-shared) = yes && subdir] (tests-special): Add
$(check-abi-list).
[$(build-shared) = yes && subdir] (tests): Do not depend on
check-abi.
* Rules (tests): Depend on $(tests-special).
(xtests): Depend on $(xtests-special).
* catgets/Makefile (tests): Change dependencies to ....
(tests-special): ... additions to this variable.
* conform/Makefile (tests): Change dependencies to ....
(tests-special): ... additions to this variable.
* elf/Makefile (tests): Change dependencies to ....
(tests-special): ... additions to this variable.
* grp/Makefile (tests): Change dependencies to ....
(tests-special): ... additions to this variable.
* iconv/Makefile (xtests): Change dependencies to ....
(xtests-special): ... additions to this variable.
* iconvdata/Makefile (tests): Change dependencies to ....
(tests-special): ... additions to this variable.
* intl/Makefile (tests): Change dependencies to ....
(tests-special): ... additions to this variable. Also add
$(objpfx)tst-gettext.out.
* io/Makefile (tests): Change dependencies to ....
(tests-special): ... additions to this variable.
* libio/Makefile (tests): Change dependencies to ....
(tests-special): ... additions to this variable.
* malloc/Makefile (tests): Change dependencies to ....
(tests-special): ... additions to this variable.
* misc/Makefile (tests): Change dependencies to ....
(tests-special): ... additions to this variable.
* nptl/Makefile (tests): Change dependencies to ....
(tests-special): ... additions to this variable.
* nptl_db/Makefile (tests): Change dependencies to ....
(tests-special): ... additions to this variable.
* posix/Makefile (tests): Change dependencies to ....
(tests-special): ... additions to this variable.
(xtests): Change dependencies to ....
(xtests-special): ... additions to this variable.
* resolv/Makefile (tests): Change dependencies to ....
(tests-special): ... additions to this variable.
(xtests): Change dependencies to ....
(xtests-special): ... additions to this variable.
* stdio-common/Makefile (tests): Change dependencies to ....
(tests-special): ... additions to this variable.
(do-tst-unbputc): Remove target.
(do-tst-printf): Likewise.
* stdlib/Makefile (tests): Change dependencies to ....
(tests-special): ... additions to this variable.
* string/Makefile (tests): Change dependencies to ....
(tests-special): ... additions to this variable.
* sysdeps/x86/Makefile (tests): Change dependencies to ....
(tests-special): ... additions to this variable.
localedata:
* Makefile (tests): Change dependencies to ....
(tests-special): ... additions to this variable.
This patch, an updated version of
<https://sourceware.org/ml/libc-alpha/2014-01/msg00193.html>, starts
the process of generating explicit PASS or FAIL status for individual
glibc tests. It's based on Tomas Dohnalek's patch
<https://sourceware.org/ml/libc-alpha/2012-10/msg00278.html>, but is
deliberately more minimal: it doesn't try to cover any tests outside
of $(tests) / $(xtests) (that's for a later patch), nor does it put
the result together in an overall summary file (again, a later patch):
it just generates the .test-result files.
Thus, this patch keeps the overall logic for when a testsuite run
finishes completely unchanged: a test failing will terminate the run.
I think we *should* move to a more conventional approach where plain
"make check" does not terminate for an individual test failure, unless
e.g. you say "make stop-on-test-failure=y check", but that sort of
policy change is best done as a separate patch once the infrastructure
is in place to generate summary files for completed test runs (which
will entirely consist of PASS and XFAIL lines if the testsuite run
reaches the point of generating them, until such a policy change is
made).
Tested x86_64.
2014-02-14 Tomas Dohnalek <tdohnale@redhat.com>
Joseph Myers <joseph@codesourcery.com>
* Makeconfig (test-name): New variable.
(evaluate-test): Likewise.
* Makerules (do-test-clean): Remove .test-result files.
(common-mostlyclean): Likewise.
* Rules ($(objpfx)%.out): Use $(evaluate-test) in both rules.
* scripts/evaluate-test.sh: New file.
If you rerun "make check" in a tree where some tests have already been
run, it will rerun ABI tests because those do not create an output
file.
This patch changes those tests to create .out files so they only get
rerun if the dependencies (on the ABI baselines and the generated
.symlist files) indicate they should be rerun.
Tested x86_64.
* Makerules (check-abi-%): Change target to
$(objpfx)check-abi-%.out.
(check-abi target): Update dependencies.
(check-abi-pattern variable): Redirect output of diff to $@.
(check-abi variable): Likewise.
* elf/Makefile (check-abi): Update dependencies.
This patch creates implicit rules to match the abifiles if
abilist-pattern is defined in the architecture Makefile. This allows
machine specific Makefiles to define different abifiles names
(for instance *-le.abilist for powerpc64le).
[BZ #15915] As described in the bug, the pattern rule for lib%.so files
in Makerules includes linkobj/libc.so as a dependency. However, the
explicit rule for linkobj/libc.so is in the top-level Makefile.
Thus, the subdirectory makefiles that include Makerules end up with an
erroneous makefile pattern rule for linkobj/libc.so that includes
itself as a dependency. The result is make warnings whenever rules
for other .so files are resolved -- and, on occasion, actual makefile
failures when a race condition causes the implicit rule to actually be
used.
This patch moves the explicit rules for linkobj/libc.so into Makerules
to clear up this problem. It also elaborates a couple of comments
that I'd initially found confusing.
