[PATCH v9 3/5] Fix assert during static startup (BZ 33326)

[Adhemerval Zanella Netto]

On 08/06/26 07:46, Florian Weimer wrote:
> * Adhemerval Zanella:
> 
> I think the general issue is not right: During startup, we should not
> use mmap to allocate the backing store.  We can preserve the assert
> message and file name by copying them to on-stack buffer.  As no user
> code should be running at this point, we do not need to be prepared for
> arbitrarily-long assert messages (but we still should have a length
> check, of course).
> 
> Can we redirect to a different assert implementation during early
> startup?

I think I can reinstate the assert wrapper [1]. I kept the assert used 
simplify the the implementation and use the same code path.  We can use
a stack allocated buffer and cap the message string, for glibc own usage we
would know when we need to increase it.

But it also raises the question whether we do copy the buffer in this case,
this assert will be only used during process startup and it would be triggered
in cases that can be considered glibc issues.

[1] https://sourceware.org/pipermail/libc-alpha/2026-March/176039.html

> 
> I'm not sure this actually works for HIDDEN_VAR_NEEDS_DYNAMIC_RELOC
> because of remaining global variable accesses in __assert_fail, but
> maybe we do not support static PIE for them anyway?
> 
>> diff --git a/elf/tst-assert-startup-static.c b/elf/tst-assert-startup-static.c
>> new file mode 100644
>> index 00000000000..9fd79a0e243
>> --- /dev/null
>> +++ b/elf/tst-assert-startup-static.c
>> @@ -0,0 +1,40 @@
>> +/* Check if assert work during program startup.
> 
> Typo: work[s]

Ack.

> 
>> diff --git a/sysdeps/loongarch/lp64/multiarch/dl-symbol-redir-ifunc.h b/sysdeps/loongarch/lp64/multiarch/dl-symbol-redir-ifunc.h
>> index 1cd204c2f69..4379770c314 100644
>> --- a/sysdeps/loongarch/lp64/multiarch/dl-symbol-redir-ifunc.h
>> +++ b/sysdeps/loongarch/lp64/multiarch/dl-symbol-redir-ifunc.h
>> @@ -20,8 +20,10 @@
>>  #define _DL_IFUNC_GENERIC_H
>>  
>>  #ifndef SHARED
>> +asm ("memcpy = __memcpy_aligned");
>>  asm ("memset = __memset_aligned");
>>  asm ("memcmp = __memcmp_aligned");
>> +asm ("__strchrnul = __strchrnul_aligned");
>>  asm ("strlen = __strlen_aligned");
>>  asm ("memcpy = __memcpy_unaligned");
>>  asm ("memmove = __memmove_unaligned");
> 
> Now memcpy is redirected twice.  The existing unconsistency between the
> *_aligned and *_unaligned variants is a bit jarring, but I don't know
> enough about the port to resolve it.

Ack, I will remove the memcpy. We can remove the unconsistency later, it
is a performance improvement.

> 
>> diff --git a/sysdeps/powerpc/powerpc64/be/multiarch/dl-symbol-redir-ifunc.h b/sysdeps/powerpc/powerpc64/be/multiarch/dl-symbol-redir-ifunc.h
>> new file mode 100644
>> index 00000000000..560f57366b2
>> --- /dev/null
>> +++ b/sysdeps/powerpc/powerpc64/be/multiarch/dl-symbol-redir-ifunc.h
>> @@ -0,0 +1,27 @@
>> +/* Symbol rediretion for loader/static initialization code.
> 
> Typo: Symbol redire[c]tion
> 
> This occurs multiple times.

Ack.

> 
>> diff --git a/sysdeps/s390/string-bitops.h b/sysdeps/s390/string-bitops.h
>> new file mode 100644
>> index 00000000000..f660d019c77
>> --- /dev/null
>> +++ b/sysdeps/s390/string-bitops.h
>> @@ -0,0 +1,27 @@
>> +/* Zero byte detection, define whether to use stdbit.h
> 
> Should say “s390 version”.
> 

Ack.

>> +/* 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.  */
> 
> Typo: additiona[l]

Ack.

> 
>> +#if __ARCH__ > 6
>> +# define HAVE_BITOPTS_WORKING 1
>> +#else
>> +# define HAVE_BITOPTS_WORKING 0
>> +#endif
> 
> Do we really support __ARCH__ == 6 and earlier?
> 
> (There's an existing issue: The file name and the macro name are
> inconsistent.)

It is still used with build-many-glibc.py toolchail.

> 
>> diff --git a/sysdeps/unix/sysv/linux/i386/dl-mmap.c b/sysdeps/unix/sysv/linux/i386/dl-mmap.c
>> new file mode 100644
>> index 00000000000..ab6f96300fb
>> --- /dev/null
>> +++ b/sysdeps/unix/sysv/linux/i386/dl-mmap.c
>> @@ -0,0 +1,36 @@
>> +/* mmap wrapper for dynamic loader.  Linux/i386 version.
> 
>> +/* This mmap call is used to allocate some memory to backup assert() messages
>> +   before TLS setup is done, so it can not use "call *%gs:SYSINFO_OFFSET"
>> +   during startup in static PIE.  */
> 
> Typo: can[]not (multiple times in the patch)

Ack.

> 
>> 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 00000000000..291f92ee14f
>> --- /dev/null
>> +++ b/sysdeps/unix/sysv/linux/i386/dl-mmap.h
>> @@ -0,0 +1,27 @@
>> +/* mmap wrapper for dynamic loader.
> 
> Should say: i386 version

Ack.

> 
>> diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
>> index 2fdd4af3eb7..a10dd30d12b 100644
>> --- a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
>> +++ b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
>> @@ -24,8 +24,16 @@ sysdep_routines += \
>>    strncmp-vector \
>>    # sysdep_routines
>>  
>> +# Called during static library initialization, so turn stack-protection
>> +# off for non-shared builds.
>> +CFLAGS-memset-generic.o = $(no-stack-protector)
>> +CFLAGS-memset-generic.op = $(no-stack-protector)
>> +CFLAGS-memcpy-generic.o = $(no-stack-protector)
>> +CFLAGS-memcpy-generic.op = $(no-stack-protector)
>> +
>>  CFLAGS-memcpy_noalignment.c += -mno-strict-align
>>  # Called during static initialization
>> +CFLAGS-strlen-generic.c += $(no-stack-protector)
>>  CFLAGS-memset-generic.c += $(no-stack-protector)
>>  CFLAGS-memcpy-generic.c += $(no-stack-protector)
>>  endif
> 
> Isn't the first block of flags changes redundant given the existing
> CFLAGS-memset-generic.c setting?

Yes, I will remove then.

> 
>> diff --git a/sysdeps/x86_64/multiarch/dl-symbol-redir-ifunc.h b/sysdeps/x86_64/multiarch/dl-symbol-redir-ifunc.h
>> index 1f3ca20307c..4d9cc5dd914 100644
>> --- a/sysdeps/x86_64/multiarch/dl-symbol-redir-ifunc.h
>> +++ b/sysdeps/x86_64/multiarch/dl-symbol-redir-ifunc.h
>> @@ -73,6 +73,28 @@ asm ("memmove = " HAVE_MEMMOVE_IFUNC_GENERIC);
>>  asm ("mempcpy = " HAVE_MEMPCPY_IFUNC_GENERIC);
>>  asm ("__mempcpy = " HAVE_MEMPCPY_IFUNC_GENERIC);
>>  
>> +
>> +#if MINIMUM_X86_ISA_LEVEL >= 4
> 
> Spurious blank line.
> 

Ack.

> Thanks,
> Florian
>