Building glibc for s390 with -Os (32-bit only, with GCC 7) fails with:
In file included from ../sysdeps/s390/multiarch/8bit-generic.c:370:0,
from ebcdic-at-de.c:28:
../iconv/loop.c: In function '__to_generic_vx':
../iconv/loop.c:264:22: error: 'ch' may be used uninitialized in this function [-Werror=maybe-uninitialized]
if (((Character) >> 7) == (0xe0000 >> 7)) \
^~
In file included from ebcdic-at-de.c:28:0:
../sysdeps/s390/multiarch/8bit-generic.c:340:15: note: 'ch' was declared here
uint32_t ch; \
^
../iconv/loop.c:325:7: note: in expansion of macro 'BODY'
BODY
^~~~
It's fairly easy to see, looking at the (long) expansion of the BODY
macro, that this is a false positive and the relevant variable 'ch' is
always initialized before use, in one of two possible places. As
such, disabling the warning for -Os with the DIAG_* macros is the
natural approach to fix this build failure. However, because of the
location at which the warning is reported, the disabling needs to go
in iconv/loop.c, around the definition of UNICODE_TAG_HANDLER (not
inside the definition), as that macro definition is where the
uninitialized use is reported, whereas the code that needs to be
reasoned about to see that the warning is a false positive is in the
definition of BODY elsewhere.
Thus, the patch adds such disabling in iconv/loop.c, with a comment
pointing to the s390-specific code and a comment in the s390-specific
code pointing to the generic file to alert people to the possible need
to update one place when changing the other. It would be possible if
desired to use #ifdef __s390__ around the disabling, though in general
we try to avoid that sort of thing in generic files. (Or some
extremely specialized macros for "disable -Wmaybe-uninitialized in
this particular place" could be specified, defined to 0 in a lot of
different files that include iconv/loop.c and to 1 in that particular
s390 file.)
Tested that this fixed -Os compilation for s390-linux-gnu with
build-many-glibcs.py.
* iconv/loop.c (UNICODE_TAG_HANDLER): Disable
-Wmaybe-uninitialized for -Os.
* sysdeps/s390/multiarch/8bit-generic.c (BODY): Add comment about
this disabling.
This patch adds s390_libc_ifunc_expr macro which uses the __ifunc base macro
in include/libc-symbols.h and lets the user define a generic expression to
choose the correct ifunc variant. Furthermore as the base macro is used,
the ifunc resolver functions are now also using inhibit_stack_protector.
S390 needs its own version due to the hwcap argument of the ifunc resolver.
This new macro is now used in iconv code in 8bit-generic.c instead of using
gcc attribute ifunc directly.
ChangeLog:
* sysdeps/s390/multiarch/ifunc-resolve.h
(s390_libc_ifunc_expr_init, s390_libc_ifunc_expr): New Define.
* sysdeps/s390/multiarch/8bit-generic.c
(__to_generic, __from_generic): Use s390_libc_ifunc_expr to
define ifunc resolvers.
This patch introduces a s390 specific 8bit-generic.c file which provides an
optimized version for z13 with translate-/vector-instructions, which will be
chosen at runtime via ifunc.
If the build-environment lacks vector support, then iconvdata/8bit-generic.c
is used wihtout any change. Otherwise iconvdata/8bit-generic.c is used to create
conversion loop routines without vector instructions as fallback, if vector
instructions aren't available at runtime.
The vector routines can only be used with charsets where the maximum UCS4 value
fits in 1 byte size. Then the hardware translate-instruction is used
to translate between up to 256 generic characters and "1 byte UCS4"
characters at once. The vector instructions are used to convert between
the "1 byte UCS4" and UCS4.
The gen-8bit.sh script in sysdeps/s390/multiarch generates the conversion
table to_ucs1. Therefore in sysdeps/s390/multiarch/Makefile is added an
override define generate-8bit-table, which is originally defined in
iconvdata/Makefile. This version calls the gen-8bit.sh in iconvdata folder
and the s390 one.
ChangeLog:
* sysdeps/s390/multiarch/8bit-generic.c: New File.
* sysdeps/s390/multiarch/gen-8bit.sh: New File.
* sysdeps/s390/multiarch/Makefile (generate-8bit-table):
New override define.
* sysdeps/s390/multiarch/iconv/skeleton.c: Likewise.
