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From: "mail@felix-potthast.de" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug dynamic-link/31663] New: Stack not aligned at _start when
 calling ld.so explicitly
Date: Fri, 19 Apr 2024 22:35:06 +0000
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X-Bugzilla-Product: glibc
X-Bugzilla-Component: dynamic-link
X-Bugzilla-Version: 2.35
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D31663

            Bug ID: 31663
           Summary: Stack not aligned at _start when calling ld.so
                    explicitly
           Product: glibc
           Version: 2.35
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: dynamic-link
          Assignee: unassigned at sourceware dot org
          Reporter: mail@felix-potthast.de
  Target Milestone: ---

Up to glibc version 2.35 the stack is not 16-byte aligned when the process =
is
entered at _start when ld.so was called explicitly.

The x86-64 SYS V ABI explicitly states it has to be aligned at that point,
though.
It also works fine when ld.so is invoked as elf interpreter.

This doesn't result in any issue most of the time because the stack
is aligned between _start and main in `sysdeps/x86_64/start.S`, for legacy
reasons probably.

I think the right place to do this alignment is at the end of ld.so.


I attached a simple example that can be build with
`gcc -nostartfiles test.S -o test`.

It runs fine when running `./test` but segfaults when running with
`/lib64/ld-linux-x86-64.so.2 ./test` due to missing stack alignment.

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