[PATCH v6 4/5] Fix assert during static startup

[Florian Weimer]

* Adhemerval Zanella:

> On i386, syscalls should not use the vDSO ("call *%gs:SYSINFO_OFFSET")
> during program status because thread point is not yet initialized.  This

typos: program startu[p], thread point[er]

> diff --git a/elf/tst-assert-startup-static.c b/elf/tst-assert-startup-static.c
> new file mode 100644
> index 0000000000..5b0dbdea32
> --- /dev/null
> +++ b/elf/tst-assert-startup-static.c
> @@ -0,0 +1,35 @@

> +/* The __tunables_init is called just before self-relocation and TLS setup,
> +   and the __libc_assert_fail is used internally for assert() calls.  */
> +extern _Noreturn __typeof (__assert_fail) __libc_assert_fail;
> +
> +void __tunables_init (char **env)
> +{
> +  __libc_assert_fail ("error", __FILE__, __LINE__, __func__);
> +}

The command should say that this is done to provoke an intentional
assert ion failure.

It's also not clear why you just write:

  assert (0);  /* This should print the usual message and not just crash.  */

> +int main (int argc, char *argv[])
> +{
> +  /* Fail with a different error code than abort().  */
> +  exit (EXIT_FAILURE);
> +}

GNU style is not to use () after function names (but I don't mind too
match).

> diff --git a/sysdeps/s390/string-bitops.h b/sysdeps/s390/string-bitops.h
> new file mode 100644
> index 0000000000..286d8975e5
> --- /dev/null
> +++ b/sysdeps/s390/string-bitops.h
> @@ -0,0 +1,27 @@
> +/* Zero byte detection, define whether to use stdbit.h

> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <http://www.gnu.org/licenses/>.  */

Please don't add new http:// URLs, use https:// instead.

Also applies to “string: Add fallback implementation for ctz/clz”.
Should this change here go into that commit, by the way?

> +/* s390x support static-pie and the libgcc implementation for
> +   __builtin_clzl/__builtin_ctzl might access extern data that is not marked
> +   as hidden, which creates additiona GOT access that is used before
> +   self-relocation.  */

typos: support[s], additiona[l]

> diff --git a/sysdeps/unix/sysv/linux/dl-mmap.h b/sysdeps/unix/sysv/linux/dl-mmap.h
> new file mode 100644
> index 0000000000..f786be0930
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/dl-mmap.h
> @@ -0,0 +1,34 @@
> +/* mmap wrapper for dynamic loader.

This doesn't seem to be needed because it matches the generic version?

> diff --git a/sysdeps/unix/sysv/linux/i386/Makefile b/sysdeps/unix/sysv/linux/i386/Makefile
> index f1f8c3f44c..a0f326229e 100644
> --- a/sysdeps/unix/sysv/linux/i386/Makefile
> +++ b/sysdeps/unix/sysv/linux/i386/Makefile
> @@ -28,3 +28,17 @@ ifeq ($(subdir),rt)
>  librt-routines += sysdep
>  librt-shared-only-routines += sysdep
>  endif
> +
> +ifeq ($(subdir),elf)
> +sysdep_routines += \
> +  dl-mmap \
> +  dl-writev \
> +  # sysdep-rtld-routines

typo: sysdep[_routines]

> diff --git a/sysdeps/unix/sysv/linux/i386/dl-mmap.h b/sysdeps/unix/sysv/linux/i386/dl-mmap.h
> new file mode 100644
> index 0000000000..3c4aec9d36
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/i386/dl-mmap.h
> @@ -0,0 +1,25 @@
> +/* mmap wrapper for dynamic loader.
> +   Copyright (C) 2026 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _DL_MMAP_H
> +#define _DL_MMAP_H
> +
> +void * _dl_mmap (void *addr, size_t len, int prot, int flags)
> +  attribute_hidden;
> +
> +#endif

This should have a comment that says that i386 needs an out-of-line
definition because it has to set define I386_USE_SYSENTER to 0.

> diff --git a/sysdeps/unix/sysv/linux/i386/dl-writev.h b/sysdeps/unix/sysv/linux/i386/dl-writev.h
> index 8327d32374..cf0459db11 100644
> --- a/sysdeps/unix/sysv/linux/i386/dl-writev.h
> +++ b/sysdeps/unix/sysv/linux/i386/dl-writev.h
> @@ -16,9 +16,12 @@
>     License along with the GNU C Library; if not, see
>     <https://www.gnu.org/licenses/>.  */
>  
> -#if BUILD_PIE_DEFAULT
> -/* Can't use "call *%gs:SYSINFO_OFFSET" during startup in static PIE.  */
> -# define I386_USE_SYSENTER 0
> -#endif
> +#ifndef _DL_WRITEV_H
> +#define _DL_WRITEV_H
>  
> -#include <sysdeps/unix/sysv/linux/dl-writev.h>
> +#include <sys/uio.h>
> +
> +ssize_t _dl_writev (int fd, const struct iovec *iov, size_t niov)
> +  attribute_hidden;
> +
> +#endif

Please add a comment here as well.


> diff --git a/sysdeps/unix/sysv/linux/i386/raise_direct.c b/sysdeps/unix/sysv/linux/i386/raise_direct.c
> new file mode 100644
> index 0000000000..d27966fc9c
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/i386/raise_direct.c
> @@ -0,0 +1,26 @@
> +/* Send a signal to a specific pthread.  Stub version.

Comment is not correct.

Overall direction seems okay.  I do wonder if we should just disable the
kernel syscall optimization for i386 static builds.  However, the
performance hit on current Intel CPUs is quite severe: getpid becomes
three times slower.  But then it's i386, so maybe for static builds
that's okay?

In the future, we might see optimization of those quasi-no-op system
calls using rseq, so a removal decision could be easier.

Thanks,
Florian