From: Alejandro Colomar <alx@kernel.org>
To: libc-alpha@sourceware.org
Cc: Alejandro Colomar <alx@kernel.org>,
Florian Weimer <fweimer@redhat.com>,
Xi Ruoyao <xry111@xry111.site>, Sam James <sam@gentoo.org>,
Richard Biener <rguenth@gcc.gnu.org>,
Andrew Pinski <apinski@marvell.com>
Subject: [RFC v1 0/2] Use -fno-delete-null-pointer-checks to build glibc
Date: Tue, 11 Jul 2023 15:11:04 +0200 [thread overview]
Message-ID: <20230711131105.19203-1-alx@kernel.org> (raw)
Hi,
Glibc currently undefines __nonnull internally, to avoid compiler
optimizations that would make glibc unsafe. The attribute is only
present in installed headers, but for internal code an #undef is used.
Xi is trying to improve the consistency in uses of __nonnull in the
installed headers, to avoid special cases in GCC's fanalyzer. That
prompted the question of whether the attribute is safe, as the compiler
is known to optimize too much based on it.
Florian reported that there's -fno-delete-null-pointer-checks to tell
the compiler to not optimize, and only warn about incorrect uses of null
pointers.
Another idea arised from that: it would be good if glibc used __nonnull
internally to get more warnings. We only need to take care to prevent
the compiler optimizations.
While I was trying to do that change, which seemed trivial (see this
patch set), I uncovered what seems some circular dependencies in the
glibc header files (see the build log below). Could you please have a
look at it?
Thanks,
Alex
---- (re)Build log ----
$ make
make -r PARALLELMFLAGS="" -C ../nonnull objdir=`pwd` all
make[1]: Entering directory '/home/alx/src/gnu/glibc/nonnull'
type "make help" for help with common glibc makefile targets
make subdir=csu -C csu ..=../ subdir_lib
make subdir=iconv -C iconv ..=../ subdir_lib
make[2]: Entering directory '/home/alx/src/gnu/glibc/nonnull/iconv'
gcc gconv_conf.c -c -std=gnu11 -fgnu89-inline -fno-delete-null-pointer-checks -g -O2 -Wall -Wwrite-strings -Wundef -Werror -fmerge-all-constants -frounding-math -fno-stack-protector -fno-common -Wp,-U_FORTIFY_SOURCE -Wstrict-prototypes -Wold-style-definition -fmath-errno -fPIE -DGCONV_PATH='"/opt/gnu/glibc/nonnull/lib/gconv"' -ftls-model=initial-exec -I../include -I/home/alx/src/gnu/glibc/.tmp/iconv -I/home/alx/src/gnu/glibc/.tmp -I../sysdeps/unix/sysv/linux/x86_64/64 -I../sysdeps/unix/sysv/linux/x86_64 -I../sysdeps/unix/sysv/linux/x86/include -I../sysdeps/unix/sysv/linux/x86 -I../sysdeps/x86/nptl -I../sysdeps/unix/sysv/linux/wordsize-64 -I../sysdeps/x86_64/nptl -I../sysdeps/unix/sysv/linux/include -I../sysdeps/unix/sysv/linux -I../sysdeps/nptl -I../sysdeps/pthread -I../sysdeps/gnu -I../sysdeps/unix/inet -I../sysdeps/unix/sysv -I../sysdeps/unix/x86_64 -I../sysdeps/unix -I../sysdeps/posix -I../sysdeps/x86_64/64 -I../sysdeps/x86_64/fpu/multiarch -I../sysdeps/x86_64/fpu -I../sysdeps/x86/fpu -I../sysdeps/x86_64/multiarch -I../sysdeps/x86_64 -I../sysdeps/x86/include -I../sysdeps/x86 -I../sysdeps/ieee754/float128 -I../sysdeps/ieee754/ldbl-96/include -I../sysdeps/ieee754/ldbl-96 -I../sysdeps/ieee754/dbl-64 -I../sysdeps/ieee754/flt-32 -I../sysdeps/wordsize-64 -I../sysdeps/ieee754 -I../sysdeps/generic -I.. -I../libio -I. -D_LIBC_REENTRANT -include /home/alx/src/gnu/glibc/.tmp/libc-modules.h -DMODULE_NAME=libc -include ../include/libc-symbols.h -DPIC -DTOP_NAMESPACE=glibc -o /home/alx/src/gnu/glibc/.tmp/iconv/gconv_conf.o -MD -MP -MF /home/alx/src/gnu/glibc/.tmp/iconv/gconv_conf.o.dt -MT /home/alx/src/gnu/glibc/.tmp/iconv/gconv_conf.o
In file included from ../include/sys/cdefs.h:10,
from ../include/features.h:503,
from ../assert/assert.h:35,
from ../include/assert.h:1,
from gconv_conf.c:19:
../include/dirent.h:53:17: error: expected ‘)’ before numeric constant
53 | __nonnull (4) attribute_hidden;
| ^
../misc/sys/cdefs.h:401:69: note: in definition of macro ‘__attribute_nonnull__’
401 | # define __attribute_nonnull__(params) __attribute__ ((__nonnull__ params))
| ^~~~~~
../include/dirent.h:53:6: note: in expansion of macro ‘__nonnull’
53 | __nonnull (4) attribute_hidden;
| ^~~~~~~~~
../misc/sys/cdefs.h:401:76: error: expected ‘,’ or ‘;’ before ‘)’ token
401 | # define __attribute_nonnull__(params) __attribute__ ((__nonnull__ params))
| ^
../misc/sys/cdefs.h:407:28: note: in expansion of macro ‘__attribute_nonnull__’
407 | # define __nonnull(params) __attribute_nonnull__ (params)
| ^~~~~~~~~~~~~~~~~~~~~
../include/dirent.h:53:6: note: in expansion of macro ‘__nonnull’
53 | __nonnull (4) attribute_hidden;
| ^~~~~~~~~
make[2]: *** [../o-iterator.mk:9: /home/alx/src/gnu/glibc/.tmp/iconv/gconv_conf.o] Error 1
make[2]: Leaving directory '/home/alx/src/gnu/glibc/nonnull/iconv'
make[1]: *** [Makefile:484: iconv/subdir_lib] Error 2
make[1]: Leaving directory '/home/alx/src/gnu/glibc/nonnull'
make: *** [Makefile:9: all] Error 2
--- Build log end ----
Alejandro Colomar (2):
Makeconfig: Use one line per token
Makeconfig: Compile glibc with -fno-delete-null-pointer-checks
Makeconfig | 18 +++++++++++++-----
include/sys/cdefs.h | 6 ------
2 files changed, 13 insertions(+), 11 deletions(-)
Range-diff against v0:
-: ---------- > 1: 55d7caa944 Makeconfig: Use one line per token
-: ---------- > 2: efb21da36c Makeconfig: Compile glibc with -fno-delete-null-pointer-checks
--
2.40.1
next reply other threads:[~2023-07-11 13:11 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-11 13:11 Alejandro Colomar [this message]
2023-07-11 13:11 ` [RFC v1 1/2] Makeconfig: Use one line per token Alejandro Colomar
2023-07-11 18:05 ` Adhemerval Zanella Netto
2023-07-11 13:11 ` [RFC v1 2/2] Makeconfig: Compile glibc with -fno-delete-null-pointer-checks Alejandro Colomar
2023-07-11 13:41 ` Florian Weimer
2023-07-11 13:53 ` Siddhesh Poyarekar
2023-07-12 10:56 ` Richard Biener
2023-07-12 12:22 ` Cristian Rodríguez
2023-07-12 12:43 ` Florian Weimer
2023-07-11 13:18 ` [RFC v1 0/2] Use -fno-delete-null-pointer-checks to build glibc Florian Weimer
2023-07-11 13:19 ` Alejandro Colomar
2023-07-11 13:22 ` Xi Ruoyao
2023-07-11 13:24 ` Alejandro Colomar
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