Fix lgamma setting signgam for ISO C (bug 15421).

The lgamma (and likewise lgammaf, lgammal) function wrongly sets the
signgam variable even when building for strict ISO C conformance
(-std=c99 / -std=c11), although the user may define such a variable
and it's only in the implementation namespace for POSIX with XSI
extensions enabled.

Following discussions starting at
<https://sourceware.org/ml/libc-alpha/2013-04/msg00767.html> and
<https://sourceware.org/ml/libc-alpha/2015-10/msg00844.html>, it seems
that the safest approach for fixing this particular issue is for
signgam to become a weak alias for a newly exported symbol __signgam,
with the library functions only setting __signgam, at which point
static linker magic will preserve the alias for newly linked binaries
that refer to the library's signgam rather than defining their own,
while breaking the alias for programs that define their own signgam,
with new symbol versions for lgamma functions and with compat symbols
for existing binaries that set both signgam and __signgam.

This patch implements that approach for the fix.  signgam is made into
a weak alias.  The four symbols __signgam, lgamma, lgammaf, lgammal
get new symbol versions at version GLIBC_2.23, with the existing
versions of lgamma, lgammaf and lgammal becoming compat symbols.

When the compat versions are built, gamma, gammaf and gammal are
aliases for the compat versions (i.e. always set signgam); this is OK
as they are not ISO C functions, and avoids adding new symbol versions
for them unnecessarily.  When the compat versions are not built
(i.e. for static linking and for future glibc ports), gamma, gammaf
and gammal are aliases for the new versions that set __signgam.  The
ldbl-opt versions are updated accordingly.

The lgamma wrappers are adjusted so that the same source files,
included from different files with different definitions of
USE_AS_COMPAT, can build either the new versions or the compat
versions.  Similar changes are made to the ia64 versions (untested).

Tests are added that the lgamma functions do not interfere with a user
variable called signgam for ISO C, with various choices for the size
of that variable, whether it is initialized, and for static and
dynamic linking.  The conformtest whitelist entry is removed as well.

Tested for x86_64, x86, mips64 and powerpc, including looking at
objdump --dynamic-syms output to make sure the expected sets of
symbols were aliases.  Also spot-tested that a binary built with old
glibc works properly (i.e. gets signgam set) when run with new glibc.

	[BZ #15421]
	* sysdeps/ieee754/s_signgam.c (signgam): Rename to __signgam,
	initialize with 0 and define as weak alias of __signgam.
	* include/math.h [!_ISOMAC] (__signgam): Declare.
	* math/Makefile (libm-calls): Add w_lgamma_compat.
	(tests): Add test-signgam-uchar, test-signgam-uchar-init,
	test-signgam-uint, test-signgam-uint-init, test-signgam-ullong and
	test-signgam-ullong-init.
	(tests-static): Add test-signgam-uchar-static,
	test-signgam-uchar-init-static, test-signgam-uint-static,
	test-signgam-uint-init-static, test-signgam-ullong-static and
	test-signgam-ullong-init-static.
	(CFLAGS-test-signgam-uchar.c): New variable.
	(CFLAGS-test-signgam-uchar-init.c): Likewise.
	(CFLAGS-test-signgam-uchar-static.c): Likewise.
	(CFLAGS-test-signgam-uchar-init-static.c): Likewise.
	(CFLAGS-test-signgam-uint.c): Likewise.
	(CFLAGS-test-signgam-uint-init.c): Likewise.
	(CFLAGS-test-signgam-uint-static.c): Likewise.
	(CFLAGS-test-signgam-uint-init-static.c): Likewise.
	(CFLAGS-test-signgam-ullong.c): Likewise.
	(CFLAGS-test-signgam-ullong-init.c): Likewise.
	(CFLAGS-test-signgam-ullong-static.c): Likewise.
	(CFLAGS-test-signgam-ullong-init-static.c): Likewise.
	* math/Versions (libm): Add GLIBC_2.23.
	* math/lgamma-compat.h: New file.
	* math/test-signgam-main.c: Likewise.
	* math/test-signgam-uchar-init-static.c: Likewise.
	* math/test-signgam-uchar-init.c: Likewise.
	* math/test-signgam-uchar-static.c: Likewise.
	* math/test-signgam-uchar.c: Likewise.
	* math/test-signgam-uint-init-static.c: Likewise.
	* math/test-signgam-uint-init.c: Likewise.
	* math/test-signgam-uint-static.c: Likewise.
	* math/test-signgam-uint.c: Likewise.
	* math/test-signgam-ullong-init-static.c: Likewise.
	* math/test-signgam-ullong-init.c: Likewise.
	* math/test-signgam-ullong-static.c: Likewise.
	* math/test-signgam-ullong.c: Likewise.
	* math/w_lgamma.c: Rename to w_lgamma_main.c and replace by
	wrapper of w_lgamma_main.c.
	* math/w_lgamma_compat.c: New file.
	* math/w_lgamma_compatf.c: Likewise.
	* math/w_lgamma_compatl.c: Likewise.
	* math/w_lgamma_main.c: New file.  Based on w_lgamma.c.  Include
	<lgamma-compat.h>.  Condition contents on [BUILD_LGAMMA].  Support
	defining compatibility symbols.
	(__lgamma): Change to LGFUNC (__lgamma).  Use CALL_LGAMMA.
	* math/w_lgammaf.c: Rename to w_lgammaf_main.c and replace by
	wrapper of w_lgammaf_main.c.
	* math/w_lgammaf_main.c: New file.  Based on w_lgammaf.c.  Include
	<lgamma-compat.h>.  Condition contents on [BUILD_LGAMMA].  Support
	defining compatibility symbols.
	(__lgammaf): Change to LGFUNC (__lgammaf).  Use CALL_LGAMMA.
	* math/w_lgammal.c: Rename to w_lgammal_main.c and replace by
	wrapper of w_lgammal_main.c.
	* math/w_lgammal_main.c: New file.  Based on w_lgammal.c.  Include
	<lgamma-compat.h>.  Condition contents on [BUILD_LGAMMA].  Support
	defining compatibility symbols.
	(__lgammal): Change to LGFUNC (__lgammal).  Use CALL_LGAMMA.
	* sysdeps/ia64/fpu/lgamma-compat.h: New file.
	* sysdeps/ia64/fpu/w_lgamma.c: Move to ....
	* sysdeps/ia64/fpu/w_lgamma_main.c: ...here.  Include
	<lgamma-compat.h>.
	(__ieee754_lgamma): Change to LGFUNC (lgamma).  Use CALL_LGAMMA.
	(__ieee754_gamma): Define as alias.
	* sysdeps/ia64/fpu/w_lgammaf.c: Move to ....
	* sysdeps/ia64/fpu/w_lgammaf_main.c: ...here.  Include
	<lgamma-compat.h>.
	(__ieee754_lgammaf): Change to LGFUNC (lgammaf).  Use CALL_LGAMMA.
	(__ieee754_gammaf): Define as alias.
	* sysdeps/ia64/fpu/w_lgammal.c: Move to ....
	* sysdeps/ia64/fpu/w_lgammal_main.c: ...here.  Include
	<lgamma-compat.h>.
	(__ieee754_lgammal): Change to LGFUNC (lgammal).  Use CALL_LGAMMA.
	(__ieee754_gammal): Define as alias.
	* sysdeps/ieee754/ldbl-opt/w_lgamma.c: Move to ....
	* sysdeps/ieee754/ldbl-opt/w_lgamma_compat.c: ...here.  Include
	<math/w_lgamma_compat.c>.
	[LONG_DOUBLE_COMPAT(libm, GLIBC_2_0)] (__lgammal_dbl_compat):
	Define as alias of __lgamma_compat and use in defining lgammal.
	* sysdeps/ieee754/ldbl-opt/w_lgammal.c: Move to ....
	* sysdeps/ieee754/ldbl-opt/w_lgamma_compatl.c: ...here.  Include
	<math/lgamma-compat.h> and <math/w_lgamma_compatl.c>.
	(USE_AS_COMPAT): New macro.
	(LGAMMA_OLD_VER): Undefine and redefine.
	(lgammal): Do not define here.
	(gammal): Only define here if [GAMMA_ALIAS].
	* conform/linknamespace.pl (@whitelist): Remove signgam.
	* sysdeps/nacl/libm.abilist: Update.
	* sysdeps/unix/sysv/linux/aarch64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/alpha/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/arm/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/hppa/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/i386/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/ia64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/m68k/coldfire/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/m68k/m680x0/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/microblaze/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/mips/mips32/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/mips/mips64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/nios2/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/fpu/libm.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/nofpu/libm.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/libm-le.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/libm.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-32/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/sh/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc32/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/tile/tilegx/tilegx32/libm.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/tile/tilegx/tilegx64/libm.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/tile/tilepro/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/x32/libm.abilist: Likewise.

1 files changed, 6 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index 4c00e1474c..df8ad62a82 100644
--- a/NEWS
+++ b/NEWS
@@ -42,6 +42,12 @@ Version 2.23
 * Optimized string, wcsmbs and memory functions for IBM z13.
   Implemented by Stefan Liebler.
 
+* Newly linked programs that define a variable called signgam will no longer
+  have it set by the lgamma, lgammaf and lgammal functions.  Programs that
+  require signgam to be set by those functions must ensure that they use the
+  variable provided by the GNU C Library and declared in <math.h>, without
+  defining their own copy.
+
 * The minimum GCC version that can be used to build this version of the GNU
   C Library is GCC 4.7.  Older GCC versions, and non-GNU compilers, can
   still be used to compile programs using the GNU C Library.