[Bug libc/29864] New: __libc_start_main() should obtain program headers address (_dl_phdr) from the auxv, not the ELF header.

[Bug libc/29864] New: __libc_start_main() should obtain program headers address (_dl_phdr) from the auxv, not the ELF header.

[yagogl at protonmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29864

            Bug ID: 29864
           Summary: __libc_start_main() should obtain program headers
                    address (_dl_phdr) from the auxv, not the ELF header.
           Product: glibc
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: yagogl at protonmail dot com
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

Created attachment 14487
  --> https://sourceware.org/bugzilla/attachment.cgi?id=14487&action=edit
A patch file with my proposed solution.

The ELF specification declares a field in the ELF header to contain the offset
inside the binary at which there will be found the program headers table:
phoff. Since a segment may see its in-memory size differ from its in-file size
(or the binary may have holes), in-memory offsets are bound to differ too from
their in-file counterparts, and hence we may commit an error using base + phoff
to find the address of the phdr's, failing miserably with a segmentation fault
with a perfectly valid ELF.
Given that the kernel so nicely provides this piece of information in the
auxiliar vector, I think it would be best to use it by default, recurring to
other ways only when this field is mysteriously ommited from it or there is no
auxiliar vector at all.

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[Bug libc/29864] __libc_start_main() should obtain program headers address (_dl_phdr) from the auxv, not the ELF header.

[yagogl at protonmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29864

Yago Gutiérrez <yagogl at protonmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #14487|0                           |1
           is patch|                            |

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[Bug libc/29864] __libc_start_main() should obtain program headers address (_dl_phdr) from the auxv, not the ELF header.

[adhemerval.zanella at linaro dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29864

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |adhemerval.zanella at linaro dot o
                   |                            |rg

--- Comment #1 from Adhemerval Zanella <adhemerval.zanella at linaro dot org> ---
Patch looks ok. Ideally, we dl_phdr would be in relro section but we do not for
other globals. Could you send it to libc-alpha? All patches are discussed
there.

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[Bug libc/29864] __libc_start_main() should obtain program headers address (_dl_phdr) from the auxv, not the ELF header.

[yagogl at protonmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29864

--- Comment #2 from Yago Gutiérrez <yagogl at protonmail dot com> ---
Yes, it has already been sent to the mailing list, unless I made something
wrong... I don't know, this is my first time submitting a patch.

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[Bug libc/29864] __libc_start_main() should obtain program headers address (_dl_phdr) from the auxv, not the ELF header.

[adhemerval.zanella at linaro dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29864

--- Comment #3 from Adhemerval Zanella <adhemerval.zanella at linaro dot org> ---
Yeah, I saw it now.

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[Bug libc/29864] __libc_start_main() should obtain program headers address (_dl_phdr) from the auxv, not the ELF header.

[adhemerval.zanella at linaro dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29864

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

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

--- Comment #4 from Adhemerval Zanella <adhemerval.zanella at linaro dot org> ---
Fixed on 2.37.

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