From: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
To: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
"debian-alpha@lists.debian.org" <debian-alpha@lists.debian.org>
Cc: gentoo-alpha@lists.gentoo.org,
GNU C Library <libc-alpha@sourceware.org>,
Florian Weimer <fweimer@redhat.com>
Subject: Re: Update on the glibc segfault issue on Alpha
Date: Tue, 3 Jan 2023 09:09:04 -0300 [thread overview]
Message-ID: <86f86d4e-b9d5-1caf-a5ac-018bb95b38bc@linaro.org> (raw)
In-Reply-To: <fd9147e3-38f6-a230-83eb-5a950b1d428a@physik.fu-berlin.de>
On 02/01/23 14:37, John Paul Adrian Glaubitz wrote:
> Hello!
>
> On 1/2/23 12:44, John Paul Adrian Glaubitz wrote:
>> Adhemerval from glibc upstream is aware of the problem but he has not found yet a solution
>> to this issue as it needs to be debugged further. I will try to bisect which particular
>> introduced the regression and file a new upstream bug report.
>>
>> During our discussion, Adhemerval pointed out that this change [3] might be the culprit
>> but I have not been able to verify this yet.
>
> My latest bisecting has shown this change to be the responsible change, CC'ing the author:
>
> commit 73fc4e28b9464f0e13edc719a5372839970e7ddb (refs/bisect/bad)
> Author: Florian Weimer <fweimer@redhat.com>
> Date: Mon Feb 28 11:50:41 2022 +0100
>
> Linux: Consolidate auxiliary vector parsing (redo)
> And optimize it slightly.
> This is commit 8c8510ab2790039e58995ef3a22309582413d3ff revised.
> In _dl_aux_init in elf/dl-support.c, use an explicit loop
> and -fno-tree-loop-distribute-patterns to avoid memset.
> Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
Thanks, this commits helps narrow down the issue. The 73fc4e28b9464f0e refactor did not
add the GL(dl_phdr) and GL(dl_phnum) for static case, relying on the __ehdr_start symbol
to get the correct values.
The issue is for some archs, alpha for instance, the hidden weak reference is not making
the static linker to define the __ehdr_start address correctly: it is being set to 0 and
thus GL(dl_phdr) and GL(dl_phnum) are set to invalid values.
And I am not sure if the hidden weak __ehdr_start does work on all architectures, so I
think it would be safer to just restore the previous behavior to setup GL(dl_phdr) and
GL(dl_phnum) for static and we can simplify __ehdr_start fallback case to not use
a weak ref (as for PIE). I am checking if the following patch trigger any regression,
at least for alpha it fixes the static failures:
diff --git a/csu/libc-start.c b/csu/libc-start.c
index 543560f36c..63a3eceaea 100644
--- a/csu/libc-start.c
+++ b/csu/libc-start.c
@@ -271,18 +271,10 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
So we can set up _dl_phdr and _dl_phnum even without any
information from auxv. */
- extern const ElfW(Ehdr) __ehdr_start
-# if BUILD_PIE_DEFAULT
- __attribute__ ((visibility ("hidden")));
-# else
- __attribute__ ((weak, visibility ("hidden")));
- if (&__ehdr_start != NULL)
-# endif
- {
- assert (__ehdr_start.e_phentsize == sizeof *GL(dl_phdr));
- GL(dl_phdr) = (const void *) &__ehdr_start + __ehdr_start.e_phoff;
- GL(dl_phnum) = __ehdr_start.e_phnum;
- }
+ extern const ElfW(Ehdr) __ehdr_start attribute_hidden;
+ assert (__ehdr_start.e_phentsize == sizeof *GL(dl_phdr));
+ GL(dl_phdr) = (const void *) &__ehdr_start + __ehdr_start.e_phoff;
+ GL(dl_phnum) = __ehdr_start.e_phnum;
}
__tunables_init (__environ);
diff --git a/sysdeps/unix/sysv/linux/dl-parse_auxv.h b/sysdeps/unix/sysv/linux/dl-parse_auxv.h
index bf9374371e..5913c9d6e5 100644
--- a/sysdeps/unix/sysv/linux/dl-parse_auxv.h
+++ b/sysdeps/unix/sysv/linux/dl-parse_auxv.h
@@ -56,6 +56,10 @@ void _dl_parse_auxv (ElfW(auxv_t) *av, dl_parse_auxv_t auxv_values)
if (GLRO(dl_sysinfo_dso) != NULL)
GLRO(dl_sysinfo) = auxv_values[AT_SYSINFO];
#endif
+#ifndef SHARED
+ GL(dl_phdr) = (void*) auxv_values[AT_PHDR];
+ GL(dl_phnum) = auxv_values[AT_PHENT];
+#endif
DL_PLATFORM_AUXV
}
next prev parent reply other threads:[~2023-01-03 12:09 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-02 11:44 John Paul Adrian Glaubitz
2023-01-02 17:37 ` John Paul Adrian Glaubitz
2023-01-03 12:09 ` Adhemerval Zanella Netto [this message]
2023-01-03 13:29 ` Florian Weimer
2023-01-03 13:47 ` Adhemerval Zanella Netto
2023-01-04 9:25 ` John Paul Adrian Glaubitz
2023-01-04 12:00 ` Adhemerval Zanella Netto
2023-01-05 11:25 ` John Paul Adrian Glaubitz
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