[Bug malloc/29624] New: errno is not cleared when entering main

[Bug malloc/29624] New: errno is not cleared when entering main

[ycliang at andestech dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29624

            Bug ID: 29624
           Summary: errno is not cleared when entering main
           Product: glibc
           Version: 2.35
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: malloc
          Assignee: unassigned at sourceware dot org
          Reporter: ycliang at andestech dot com
  Target Milestone: ---

According to the ANSI C standard "7.5 Errors <errno.h>" section 3[1], 
"The value of errno is zero at program startup,
but is never set to zero by any library function."

The "program startup" is also defined in ANSI C standard 
"5.1.2.2.1 Program startup" section 1[2],
"The function called at program startup is named main."

Therefore, it should be reasonable to expect 
errno be zero when main is executed.

However, we found that 
the following program would get non-zero errno under some circumstances.

```
/* errno.c */
#include <errno.h>
#include <stdio.h>

int main()
{
        printf("errno: %d\n", errno);
        return 0;
}


$ riscv64-linux-gcc -O0 -g -static -o errno_st errno.c

[   51.968765] random: fast init done
/mnt # ./errno
errno: 11

[   51.968765] random: fast init done
[  262.517056] crng init done
/mnt # ./errno
errno: 0
```

If the above program is statically-linked, 
and if the program is executed before "crng init done",
the errno will not be zero when entering main.

There seems to be syscall (__getrandom) before main is entered,
and if the crng is not initialized, 
the syscall will fail causing the errno to be set.
(_dl_get_origin -> __libc_malloc -> ptmalloc_init -> tcache_key_initialize ->
__getrandom)

Thanks to Florian's suggestion:
"Hiding the getrandom failure is probably sufficient.  All other
failures in malloc will lead to the process failing to start, so those
errors don't need to be masked."

We should clear the errno for the getrandom failure

Related discussion:
https://sourceware.org/pipermail/libc-help/2022-September/006301.html

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[Bug malloc/29624] errno is not cleared when entering main

[adhemerval.zanella at linaro dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29624

Adhemerval Zanella <adhemerval.zanella at linaro dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |adhemerval.zanella at linaro dot o
                   |                            |rg
   Target Milestone|---                         |2.37
         Resolution|---                         |FIXED
             Status|UNCONFIRMED                 |RESOLVED
           Assignee|unassigned at sourceware dot org   |adhemerval.zanella at linaro dot o
                   |                            |rg

--- Comment #1 from Adhemerval Zanella <adhemerval.zanella at linaro dot org> ---
Fixed on 2.37.

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[Bug malloc/29624] errno is not cleared when entering main

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29624

--- Comment #2 from Sourceware Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Andreas K. Huttel
<dilfridge@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=5a85786a9005722be7cb9e70f8874a5f1130daea

commit 5a85786a9005722be7cb9e70f8874a5f1130daea
Author: Xi Ruoyao <xry111@xry111.site>
Date:   Thu Jan 4 21:41:20 2024 +0800

    Make __getrandom_nocancel set errno and add a _nostatus version

    The __getrandom_nocancel function returns errors as negative values
    instead of errno.  This is inconsistent with other _nocancel functions
    and it breaks "TEMP_FAILURE_RETRY (__getrandom_nocancel (p, n, 0))" in
    __arc4random_buf.  Use INLINE_SYSCALL_CALL instead of
    INTERNAL_SYSCALL_CALL to fix this issue.

    But __getrandom_nocancel has been avoiding from touching errno for a
    reason, see BZ 29624.  So add a __getrandom_nocancel_nostatus function
    and use it in tcache_key_initialize.

    Signed-off-by: Xi Ruoyao <xry111@xry111.site>
    Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
    Signed-off-by: Andreas K. Hüttel <dilfridge@gentoo.org>

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