From: Florian Weimer <fweimer@redhat.com>
To: Carlos O'Donell <carlos@redhat.com>
Cc: libc-alpha@sourceware.org
Subject: Re: [PATCH v3] Detect ld.so and libc.so version inconsistency during startup
Date: Wed, 24 Aug 2022 09:51:39 +0200 [thread overview]
Message-ID: <87zgfu84fo.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <dbb504c0-b6b7-0c30-cdf2-e13b90db0ee4@redhat.com> (Carlos O'Donell's message of "Tue, 23 Aug 2022 22:59:04 -0400")
* Carlos O'Donell:
> On 8/23/22 17:31, Florian Weimer wrote:
>> The files NEWS, include/link.h, and sysdeps/generic/ldsodefs.h
>> contribute to the version fingerprint used for detection. The
>> fingerprint can be further refined using the --with-extra-version-id
>> configure argument.
>>
>> _dl_call_libc_early_init is replaced with _dl_lookup_libc_early_init.
>> The new function is used store a pointer to libc.so's
>> __libc_early_init function in the libc_map_early_init member of the
>> ld.so namespace structure. This function pointer can then be called
>> directly, so the separate invocation function is no longer needed.
>>
>> The versioned symbol lookup needs the symbol versioning data
>> structures, so the initialization of libc_map and libc_map_early_init
>> is now done from _dl_check_map_versions, after this information
>> becomes available. (_dl_map_object_from_fd does not set this up
>> in time, so the initialization code had to be moved from there.)
>> This means that the separate initialization code can be removed from
>> dl_main because _dl_check_map_versions covers all maps, including
>> the initial executable loaded by the kernel. The lookup still happens
>> before relocation and the invocation of IFUNC resolvers, so IFUNC
>> resolvers are protected from ABI mismatch.
>>
>> The __libc_early_init function pointer is not protected because
>> so little code runs between the pointer write and the invocation
>> (only dynamic linker code and IFUNC resolvers).
>
> This is really an exciting change since it adds a diagnostic and clean exit
> for a case that was previously a mysterious crash. Thanks for working through
> this change.
>
> v3 LGTM.
>
> Tested-by: Carlos O'Donell <carlos@redhat.com>
> Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Thanks. I can't merge this as-is because we have
| if not hasattr(enum, 'IntFlag'):
| import sys
| sys.stdout.write(
| 'warning: glibcelf.py needs Python 3.6 for enum support\n')
| sys.exit(77)
in scripts/glibcelf.py. We use glibcelf.py at build time with this
patch, so this will move the minumum Python requirement to 3.6. I guess
I should have added the hash function directly to the new script.
I'll see if I can clean up scripts/glibcelf.py today and make it
compatible with earlier Python versions.
Thanks,
Florian
prev parent reply other threads:[~2022-08-24 7:51 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-23 21:31 Florian Weimer
2022-08-24 2:59 ` Carlos O'Donell
2022-08-24 7:51 ` Florian Weimer [this message]
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