Patch ce7eb0e903 ("nptl: Cleanup cancellation macros") changed the
join sequence for internal common __pthread_timedjoin_ex to use the
new macro lll_wait_tid. The idea was this macro would issue the
cancellable futex operation depending whether the timeout is used or
not. However if a timeout is used, __lll_timedwait_tid is called and
it is not a cancellable entrypoint.
This patch fixes it by simplifying the code in various ways:
- Instead of adding the cancellation handling on __lll_timedwait_tid,
it moves the generic implementation to pthread_join_common.c (called
now timedwait_tid with some fixes to use the correct type for pid).
- The llvm_wait_tid macro is removed, along with its replication on
x86_64, i686, and sparc arch-specific lowlevellock.h.
- sparc32 __lll_timedwait_tid is also removed, since the code is similar
to generic one.
- x86_64 and i386 provides arch-specific __lll_timedwait_tid which is
also removed since they are similar in functionality to generic C code
and there is no indication it is better than compiler generated code.
New tests, tst-join8 and tst-join9, are provided to check if
pthread_timedjoin_np acts as a cancellation point.
Checked on x86_64-linux-gnu, i686-linux-gnu, sparcv9-linux-gnu, and
aarch64-linux-gnu.
[BZ #24215]
* nptl/Makefile (lpthread-routines): Remove lll_timedwait_tid.
(tests): Add tst-join8 tst-join9.
* nptl/lll_timedwait_tid.c: Remove file.
* sysdeps/sparc/sparc32/lll_timedwait_tid.c: Likewise.
* sysdeps/unix/sysv/linux/i386/lll_timedwait_tid.c: Likewise.
* sysdeps/sysv/linux/x86_64/lll_timedwait_tid.c: Likewise.
* nptl/pthread_join_common.c (timedwait_tid): New function.
(__pthread_timedjoin_ex): Act as cancellation entrypoint is block
is set.
* nptl/tst-join5.c (thread_join): New function.
(tf1, tf2, do_test): Use libsupport and add pthread_timedjoin_np
check.
* nptl/tst-join8.c: New file.
* nptl/tst-join9.c: Likewise.
* sysdeps/nptl/lowlevellock-futex.h (lll_futex_wait_cancel,
lll_futex_timed_wait_cancel): Add generic macros.
* sysdeps/nptl/lowlevellock.h (__lll_timedwait_tid, lll_wait_tid):
Remove definitions.
* sysdeps/unix/sysv/linux/i386/lowlevellock.h: Likewise.
* sysdeps/unix/sysv/linux/sparc/lowlevellock.h: Likewise.
* sysdeps/unix/sysv/linux/x86_64/lowlevellock.h: Likewise.
* sysdeps/sparc/sparc32/lowlevellock.c (__lll_timedwait_tid):
Remove function.
* sysdeps/unix/sysv/linux/i386/lowlevellock.S (__lll_timedwait_tid):
Likewise.
* sysdeps/unix/sysv/linux/x86_64/lowlevellock.S: Likewise.
* sysdeps/unix/sysv/linux/lowlevellock-futex.h
(lll_futex_timed_wait_cancel): New macro.
Add a malloc micro benchmark to enable accurate testing of the
various paths in malloc and free. The benchmark does a varying
number of allocations of a given block size, then frees them again.
It tests 3 different scenarios: single-threaded using main arena,
multi-threaded using thread-arena, main arena with SINGLE_THREAD_P
false.
* benchtests/Makefile: Add malloc-simple benchmark.
* benchtests/bench-malloc-simple.c: New benchmark.
The ORIG_SRC argument is likely a useless relic from the original
correctness tests that are not needed in the benchmarks. Remove the
argument and use S1 to point to the source to avoid confusion.
* benchtests/bench-memmove.c (do_one_test): Remove unused
ORIG_SRC.
(do_test): Adjust.
* benchtests/bench-memmove-large.c (do_one_test): Remove unused
ORIG_SRC.
(do_test): Adjust.
The clone.S patch fixes 2 elfutils testsuite unwind failures, where the
backtrace gets stuck repeating __thread_start until we hit the backtrace
limit. This was confirmed by building and installing a patched glibc and
then building elfutils and running its testsuite.
Unfortunately, the testcase isn't working as expected and I don't know why.
The testcase passes even when my clone.S patch is not installed. The testcase
looks logically similarly to the elfutils testcases that are failing. Maybe
there is a subtle difference in how the glibc unwinding works versus the
elfutils unwinding? I don't have good gdb pthread support yet, so I haven't
found a way to debug this. Anyways, I don't know if the testcase is useful or
not. If the testcase isn't useful then maybe the clone.S patch is OK without
a testcase?
Jim
[BZ #24040]
* elf/Makefile (CFLAGS-tst-unwind-main.c): Add -DUSE_PTHREADS=0.
* elf/tst-unwind-main.c: If USE_PTHEADS, include pthread.h and error.h
(func): New.
(main): If USE_PTHREADS, call pthread_create to run func. Otherwise
call func directly.
* nptl/Makefile (tests): Add tst-unwind-thread.
(CFLAGS-tst-unwind-thread.c): Define.
* nptl/tst-unwind-thread.c: New file.
* sysdeps/unix/sysv/linux/riscv/clone.S (__thread_start): Mark ra
as undefined.
In two places in glibc, -Wextra produces implicit-fallthrough warnings
where there are comments about the fall-through but their wording
doesn't match one of the forms expected by the default
implicit-fallthrough level. This patch adjusts those two places to
have a comment in a form that is accepted, so avoiding the warning
(this seems preferable to only being able to use a looser level of the
warning that allows any comment at all as evidence of deliberate
fall-through).
Tested for x86_64.
* iconvdata/cns11643.h (ucs4_to_cns11643): Adjust fall-through
comment wording.
* nis/nis_call.c (__do_niscall3): Likewise.
One group of warnings seen building glibc with -Wextra is -Wempty-body
warnings about an 'if' body (or in one case an 'else' body) that is
just a semicolon, "warning: suggest braces around empty body in an
'if' statement [-Wempty-body]" - I think the point of the warning
being to make it more visible whether an 'if' body is actually present
or not.
This patch fixes such warnings in glibc. There's one place, with a
semicolon at the end of a comment, where this is clearly making the
presence of an 'else' body more visible. The other cases involve
macro definitions expanding to nothing. While there's no issue there
with visibility at the call sites, I think it's still cleaner to have
a macro that expands to something nonempty appropriate for the context
- so do {} while (0) if it's only intended to be usable as a
statement, or ((void) 0) where the macro definition is an alternative
to a call to a function returning void, so this patch makes those
changes.
Tested for x86_64.
* catgets/gencat.c (normalize_line): Use braces around empty
'else' body.
* include/stap-probe.h [!USE_STAP_PROBE && !__ASSEMBLER__]
(STAP_PROBE0): Use do {} while (0) for do-nothing definition.
[!USE_STAP_PROBE && !__ASSEMBLER__] (STAP_PROBE1): Likewise.
[!USE_STAP_PROBE && !__ASSEMBLER__] (STAP_PROBE2): Likewise.
[!USE_STAP_PROBE && !__ASSEMBLER__] (STAP_PROBE3): Likewise.
[!USE_STAP_PROBE && !__ASSEMBLER__] (STAP_PROBE4): Likewise.
* libio/libio.h (_IO_funlockfile): Use ((void) 0) for do-nothing
definition.
One of the implicit-fallthrough warnings from compiling glibc with
-Wextra appears to indicate an actual bug: the test-container code
could fall through inappropriately if execlp returns (which only
occurs on error). This patch adds appropriate error handling in this
case to avoid that fall-through.
Tested for x86_64.
* support/test-container.c (recursive_remove): Use FAIL_EXIT1 if
execlp returns.
This change moves the audit module loading and early notification into
separate functions out of dl_main.
It restores the bug fix from commit
8e889c5da3 ("elf: Fix LD_AUDIT for
modules with invalid version (BZ#24122)") which was reverted in commit
83e6b59625 ("[elf] Revert 8e889c5da3
(BZ#24122)").
The actual bug fix is the separate error message for the case when
la_version returns zero. The dynamic linker error message (which is
NULL in this case) is no longer used. Based on the intended use of
version zero (ignore this module due to explicit request), the message
is only printed if debugging is enabled.
This patch adds fall-through comments in some cases where -Wextra
produces implicit-fallthrough warnings.
The patch is non-exhaustive. Apart from architecture-specific code
for non-x86_64 architectures, it does not change sunrpc/xdr.c (legacy
code, probably should have such changes, but left to be dealt with
separately), or places that already had comments about the
fall-through but not matching the form expected by
-Wimplicit-fallthrough=3 (the default level with -Wextra; my
inclination is to adjust those comments to match rather than
downgrading to -Wimplicit-fallthrough=1 to allow any comment), or one
place where I thought the implicit fallthrough was not correct and so
should be handled separately as a bug fix. I think the key thing to
consider in review of this patch is whether the fall-through is indeed
intended and correct in each place where such a comment is added.
Tested for x86_64.
* elf/dl-exception.c (_dl_exception_create_format): Add
fall-through comments.
* elf/ldconfig.c (parse_conf_include): Likewise.
* elf/rtld.c (print_statistics): Likewise.
* locale/programs/charmap.c (parse_charmap): Likewise.
* misc/mntent_r.c (__getmntent_r): Likewise.
* posix/wordexp.c (parse_arith): Likewise.
(parse_backtick): Likewise.
* resolv/ns_ttl.c (ns_parse_ttl): Likewise.
* sysdeps/x86/cpu-features.c (init_cpu_features): Likewise.
* sysdeps/x86_64/dl-machine.h (elf_machine_rela): Likewise.
The type used within e_sqrt.c(__slow_ieee754_sqrtf) was, unnecessarily and
likely inadvertently, double. float is not only appropriate, but also
more efficient, avoiding the need for the compiler to emit a
round-to-single-precision instruction.
This is the difference in compiled code:
0000000000000000 <__ieee754_sqrtf>:
0: 2c 08 20 ec fsqrts f1,f1
- 4: 18 08 20 fc frsp f1,f1
- 8: 20 00 80 4e blr
+ 4: 20 00 80 4e blr
(Found by Anton Blanchard.)
Having checked the arrangement of whitespace in time/strftime_l.c
using "unexpand" and "unexpand -a" command, three inconsistencies are
detected. So fix them for consistency.
ChangeLog:
* time/strftime_l.c: Fix a few whitespace arrangement inconsistencies.
Continuing the process of moving away from having bits/mathinline.h
headers in glibc, leaving the compiler to inline functions as
appropriate depending on the options passed to it, this patch removes
the header for powerpc.
<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88558> is the
corresponding GCC bug for adding replacements for these powerpc
(32-bit-only) lrint / lrintf inlines.
Tested with build-many-glibcs.py for its powerpc configurations.
* sysdeps/powerpc/bits/mathinline.h: Remove.
sysdeps/ia64/fpu/bits/math-finite.h exists and will be installed on
ia64, but during the build, the default math/bits/math-finite.h file
is used, which is wrong.
Fixes commit 0ac5ae2335 ("Optimize
libm").
No functional change; the previous path worked as well, but it
re-added the obsolete sysdeps/generic/bits directory, which was
removed (for the first time) in commit
c72565e5f1.
Fixes commit e47d82c99a ("Provide
<bits/unistd_ext.h> as a sysdeps header exclusively").
When the /etc/hosts file has a line longer than 1028
characters getent ahostsv4 and ahostsv6 will fail.
This test performs a getent call on a /etc/hosts file that contains
a very long line (greater than 1028) using the test-in-container
framework.
Non-sysdeps headers cannot be overriden by sysdeps headers across the
entire build, so it is necessary to turn such extension headers into
sysdeps headers themselves. The approach here follows the existing
<bits/shm.h> header (although it uses sysdeps/gnu instead of
sysdeps/generic).
Fixes commit 1d0fc21382 ("Linux: Add
gettid system call wrapper [BZ #6399]") and commit
8f89ab216f ("posix: Fix missing wrapper
header for <bits/unistd_ext.h>").
Commit 27761a1042 ("Refactor atfork
handlers") introduced a lock, atfork_lock, around fork handler list
accesses. It turns out that this lock occasionally results in
self-deadlocks in malloc/tst-mallocfork2:
(gdb) bt
#0 __lll_lock_wait_private ()
at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:63
#1 0x00007f160c6f927a in __run_fork_handlers (who=(unknown: 209394016),
who@entry=atfork_run_prepare) at register-atfork.c:116
#2 0x00007f160c6b7897 in __libc_fork () at ../sysdeps/nptl/fork.c:58
#3 0x00000000004027d6 in sigusr1_handler (signo=<optimized out>)
at tst-mallocfork2.c:80
#4 sigusr1_handler (signo=<optimized out>) at tst-mallocfork2.c:64
#5 <signal handler called>
#6 0x00007f160c6f92e4 in __run_fork_handlers (who=who@entry=atfork_run_parent)
at register-atfork.c:136
#7 0x00007f160c6b79a2 in __libc_fork () at ../sysdeps/nptl/fork.c:152
#8 0x0000000000402567 in do_test () at tst-mallocfork2.c:156
#9 0x0000000000402dd2 in support_test_main (argc=1, argv=0x7ffc81ef1ab0,
config=config@entry=0x7ffc81ef1970) at support_test_main.c:350
#10 0x0000000000402362 in main (argc=<optimized out>, argv=<optimized out>)
at ../support/test-driver.c:168
If no locking happens in the single-threaded case (where fork is
expected to be async-signal-safe), this deadlock is avoided.
(pthread_atfork is not required to be async-signal-safe, so a fork
call from a signal handler interrupting pthread_atfork is not
a problem.)
This commit adds gettid to <unistd.h> on Linux, and not to the
kernel-independent GNU API.
gettid is now supportable on Linux because too many things assume a
1:1 mapping between libpthread threads and kernel threads.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
As the result of commit 6e6249d0b4
("BZ#14743: Move clock_* symbols from librt to libc."), in glibc 2.17,
clock_gettime, clock_getres, clock_settime, clock_getcpuclockid,
clock_nanosleep were added to libc, and the file rt/clock-compat.c
was added with forwarders to the actual implementations in libc.
These forwarders were wrapped in
#if SHLIB_COMPAT (librt, GLIBC_2_2, GLIBC_2_17)
so that they are not present for newer architectures (such as
powerpc64le) with a 2.17 or later ABI baseline. But the forwarders
were not marked as compatibility symbols. As a result, on older
architectures, historic configure checks such as
AC_CHECK_LIB(rt, clock_gettime)
still cause linking against librt, even though this is completely
unnecessary. It also creates a needless porting hazard because
architectures behave differently when it comes to symbol availability.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
While debugging a kernel warning, Thomas Gleixner, Sebastian Sewior and
Heiko Carstens found a bug in pthread_mutex_trylock due to misordered
instructions:
140: a5 1b 00 01 oill %r1,1
144: e5 48 a0 f0 00 00 mvghi 240(%r10),0 <--- THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
14a: e3 10 a0 e0 00 24 stg %r1,224(%r10) <--- last THREAD_SETMEM of ENQUEUE_MUTEX_PI
vs (with compiler barriers):
140: a5 1b 00 01 oill %r1,1
144: e3 10 a0 e0 00 24 stg %r1,224(%r10)
14a: e5 48 a0 f0 00 00 mvghi 240(%r10),0
Please have a look at the discussion:
"Re: WARN_ON_ONCE(!new_owner) within wake_futex_pi() triggerede"
(https://lore.kernel.org/lkml/20190202112006.GB3381@osiris/)
This patch is introducing the same compiler barriers and comments
for pthread_mutex_trylock as introduced for pthread_mutex_lock and
pthread_mutex_timedlock by commit 8f9450a0b7
"Add compiler barriers around modifications of the robust mutex list."
ChangeLog:
[BZ #24180]
* nptl/pthread_mutex_trylock.c (__pthread_mutex_trylock):
Do not use a statement expression in array_length, so that
array_length can be used at file scope and as a constant expression.
Instead, put the _Static_assert into a struct (as a declaration),
and nest this in the expression using a sizeof expression.
One group of warnings seen with -Wextra is warnings for static or
inline not at the start of a declaration (-Wold-style-declaration).
This patch fixes various such cases for inline, ensuring it comes at
the start of the declaration (after any static). A common case of the
fix is "static inline <type> __always_inline"; the definition of
__always_inline starts with __inline, so the natural change is to
"static __always_inline <type>". Other cases of the warning may be
harder to fix (one pattern is a function definition that gets
rewritten to be static by an including file, "#define funcname static
wrapped_funcname" or similar), but it seems worth fixing these cases
with inline anyway.
Tested for x86_64.
* elf/dl-load.h (_dl_postprocess_loadcmd): Use __always_inline
before return type, without separate inline.
* elf/dl-tunables.c (maybe_enable_malloc_check): Likewise.
* elf/dl-tunables.h (tunable_is_name): Likewise.
* malloc/malloc.c (do_set_trim_threshold): Likewise.
(do_set_top_pad): Likewise.
(do_set_mmap_threshold): Likewise.
(do_set_mmaps_max): Likewise.
(do_set_mallopt_check): Likewise.
(do_set_perturb_byte): Likewise.
(do_set_arena_test): Likewise.
(do_set_arena_max): Likewise.
(do_set_tcache_max): Likewise.
(do_set_tcache_count): Likewise.
(do_set_tcache_unsorted_limit): Likewise.
* nis/nis_subr.c (count_dots): Likewise.
* nptl/allocatestack.c (advise_stack_range): Likewise.
* sysdeps/ieee754/dbl-64/s_sin.c (do_cos): Likewise.
(do_sin): Likewise.
(reduce_sincos): Likewise.
(do_sincos): Likewise.
* sysdeps/unix/sysv/linux/x86/elision-conf.c
(do_set_elision_enable): Likewise.
(TUNABLE_CALLBACK_FNDECL): Likewise.
In the i386 case, it appears that the sole remaining LIBC_PROBE was
removed in commit a9fe4c5aa8 ("Support
six-argument syscalls from C for 32-bit x86, use generic
lowlevellock-futex.h (bug 18138)."), when
sysdeps/unix/sysv/linux/i386/lowlevellock-futex.h was replaced with
the generic version.
For x86_64, the relevant change is commit
76f71081cd ("Use generic
lowlevellock-futex.h in x86_64 lowlevellock.h."), again by using the
generic version of <lowlevellock-futex.h>.
Tested on i386 and x86_64, with and without --enable-systemtap.
On big endian systems the test fails with:
tst-bz24153.c:88: numeric comparison failure
left: 1660944385 (0x63000001); from: ch
right: 99 (0x63); from: L'c'
tst-bz24153.c:90: numeric comparison failure
left: 1677721601 (0x64000001); from: ch
right: 100 (0x64); from: L'd'
error: 2 test failures
One 'char' ("%c") is stored to the 'wchar_t *':
ch = 0x00000001 | 0x63000000
This patch is using "%lc" as format specifier to read a wchar_t.
ChangeLog:
* libio/tst-bz24153.c (wide): Use wide char format specifier.
The recent commit 65f7767a91
has introduced __wmemcmp and the weak alias wmemcmp.
This patch also introduces those symbols if glibc is build
with CFLAGS="-march=z13" where the ifunc is omitted.
ChangeLog:
* sysdeps/s390/wmemcmp-vx.S: Add strong alias to
__wmemcmp and weak alias to wmemcmp.
The alignment of TLS variables is wrong if accessed from within a thread
for architectures with tls variant TLS_TCB_AT_TP.
For the main thread the static tls data is properly aligned.
For other threads the alignment depends on the alignment of the thread
pointer as the static tls data is located relative to this pointer.
This patch adds this alignment for TLS_TCB_AT_TP variants in the same way
as it is already done for TLS_DTV_AT_TP. The thread pointer is also already
properly aligned if the user provides its own stack for the new thread.
This patch extends the testcase nptl/tst-tls1.c in order to check the
alignment of the tls variables and it adds a pthread_create invocation
with a user provided stack.
The test itself is migrated from test-skeleton.c to test-driver.c
and the missing support functions xpthread_attr_setstack and xposix_memalign
are added.
ChangeLog:
[BZ #23403]
* nptl/allocatestack.c (allocate_stack): Align pointer pd for
TLS_TCB_AT_TP tls variant.
* nptl/tst-tls1.c: Migrate to support/test-driver.c.
Add alignment checks.
* support/Makefile (libsupport-routines): Add xposix_memalign and
xpthread_setstack.
* support/support.h: Add xposix_memalign.
* support/xthread.h: Add xpthread_attr_setstack.
* support/xposix_memalign.c: New File.
* support/xpthread_attr_setstack.c: Likewise.
With the default "nor" constraint, current GCC will use the "o"
constraint for constants, after emitting the constant to memory. That
results in unparseable Systemtap probe notes such as "-4@.L1052".
Removing the "o" alternative and using "nr" instead avoids this.
One of the warnings that appears with -Wextra is "ordered comparison
of pointer with integer zero" in malloc.c:tcache_get, for the
assertion:
assert (tcache->entries[tc_idx] > 0);
Indeed, a "> 0" comparison does not make sense for
tcache->entries[tc_idx], which is a pointer. My guess is that
tcache->counts[tc_idx] is what's intended here, and this patch changes
the assertion accordingly.
Tested for x86_64.
* malloc/malloc.c (tcache_get): Compare tcache->counts[tc_idx]
with 0, not tcache->entries[tc_idx].
I'm looking at the warnings from building glibc with -Wextra, to see
if we could use -Wextra by default, possibly with a few of its
warnings disabled, and so benefit from warnings in -Wextra but not in
-Wall. (The vast bulk of the extra warnings so produced are from
-Wunused-parameter -Wsign-compare -Wmissing-field-initializers
-Wtype-limits, so I expect those would be disabled at least at first.)
Various miscellaneous warnings show up with -Wextra that it clearly
seems to make sense to fix independent of whether we add -Wextra to
the normal options for building glibc. This patch fixes one:
"initialized field overwritten [-Woverride-init]" in nscd.
Tested for x86_64.
* nscd/connections.c (reqinfo): Initialize SHUTDOWN element only
once.
This fixes the same bug in fnmatch that was fixed by commit 7e2f0d2d77 for
regexp matching. As a side effect it also removes the use of an unbound
VLA.
Since the size argument is unsigned. we should use unsigned Jcc
instructions, instead of signed, to check size.
Tested on x86-64 and x32, with and without --disable-multi-arch.
[BZ #24155]
CVE-2019-7309
* NEWS: Updated for CVE-2019-7309.
* sysdeps/x86_64/memcmp.S: Use RDX_LP for size. Clear the
upper 32 bits of RDX register for x32. Use unsigned Jcc
instructions, instead of signed.
* sysdeps/x86_64/x32/Makefile (tests): Add tst-size_t-memcmp-2.
* sysdeps/x86_64/x32/tst-size_t-memcmp-2.c: New test.
By ordering the suballocations by decreasing alignment, alignment
gaps can be avoided.
Also use __glibc_unlikely for reading the transitions and type
indexes. In the 8-byte case, two reads are now needed because the
transitions and type indexes are no longer adjacent. The separate
call to __fread_unlocked does not matter from a performance point of
view because __tzfile_read is only invoked rarely.
The computation of tzspec_len is moved in front of the total_size
computation, so that the allocation size computation and the
suballocations are next to each other. Also add an assert that
tzspec_len is positive when it is actually used later.
When running the testsuite, building stdlib/isomac.c outputs the
following warning:
gcc -O -D_GNU_SOURCE -DIS_IN_build -include /home/aurel32/glibc-build/config.h isomac.c -o /home/aurel32/glibc-build/stdlib/isomac
isomac.c: In function ‘get_null_defines’:
isomac.c:260:3: warning: implicit declaration of function ‘close’; did you mean ‘pclose’? [-Wimplicit-function-declaration]
close (fd);
^~~~~
pclose
Fix that by adding the <unistd.h> include.
Changelog:
* stdlib/isomac.c: Include <unistd.h>.
The GMT offset can be outside the range of a 16-bit int type, which
is presumably the reason why long int was used in struct tm. We
cannot change struct tm, but we can change the internal type for
the offset.
On Linux, we define _POSIX_PRIORITY_SCHEDULING, but functions such
as sched_setparam and sched_setscheduler apply to individual threads,
not processes.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
As discussed during development for glibc 2.29, when we increased the
required minimum GCC version for building glibc to GCC 5, working
purely based on the times at which such requirements have been
increased in the past it would be appropriate for glibc 2.30 to
require GCC 6 (matching GCC 4.9 having been required for glibc 2.26).
Naming 6.2 specifically as the minimum version then means a separate
version requirement no longer needs to be specified for powerpc64le.
Thus, this patch increases the minimum to 6.2, removing the
documentation of the separate requirement for powerpc64le. It does
not remove the powerpc64le configure test, or any __GNUC_PREREQ that
could be removed as not being in installed headers or files shared
with gnulib; I think such cleanups are best done separately.
Tested for x86_64.
* configure.ac (libc_cv_compiler_ok): Require GCC 6.2 or later.
* configure: Regenerated.
* manual/install.texi (Tools for Compilation): Update minimum GCC
version.
* INSTALL: Regenerated.
