Re: [PATCH] elf,nptl: Add -z lazy -z norelro to tests that need it

["Arsen Arsenović" <arsen@gentoo.org>]

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Arsen Arsenović <arsen@gentoo.org> writes:

> Hm.  Something went awry while I was debugging this.  I looked at a test
> again just now and noticed that the symbols some of these tests were
> crashing on came from libc (dlopen here) while loading constload2 (which
> is dlopen'd from constload1).  The backtrace contains a PLT trampoline
> which then fixups dlopen inside the RELRO segment.
>
> I take it dlopen@got[plt] is not supposed to be in the RELRO range?
>
> I could have sworn this failed when fixing up bar (void) as a result of
> constload2 dlopening constload3... but maybe that was a different
> failure.
>
> Let's put this patch on hold while I investigate further.
>
> FWIW, this should be easy to reproduce by building with CC='gcc
> -Wl,-z,relro,-z,now' or so, I think.

Ah, I think I see the issue:

  ~/gnu/glibc/b2$ diff -u0 shlib.lds.-Wl,-z,{lazy,now},-z,relro 
  --- shlib.lds.-Wl,-z,lazy,-z,relro	2023-03-04 19:54:42.977032934 +0100
  +++ shlib.lds.-Wl,-z,now,-z,relro	2023-03-04 18:57:03.195010040 +0100
  @@ -1 +1 @@
  -/* Script for -shared -z combreloc -z separate-code */
  +/* Script for -shared -z combreloc -z separate-code -z relro -z now */
  @@ -153,3 +153,2 @@
  -  .got            : { *(.got) *(.igot) }
  -  . = DATA_SEGMENT_RELRO_END (SIZEOF (.got.plt) >= 24 ? 24 : 0, .);
  -  .got.plt        : { *(.got.plt) *(.igot.plt) }
  +  .got            : { *(.got.plt) *(.igot.plt) *(.got) *(.igot) }
  +  . = DATA_SEGMENT_RELRO_END (0, .);
  ~/gnu/glibc/b2 1 $ 

The builds system assumes that all the flags used while building glibc
use the same linker script, and that this will be the same linker script
as the one that's used initially to generate shlib.lds.  This is not
true when -z relro is set and -z {now,lazy} are being varied.

This also explains why the problem only arose after we introduced
-Wl,-z,now.

Do the tests even need to use this linker script?  If not, it's probably
best to just not use it for tests.  I can wire that case up, if you
think that is sensible.

Thanks in advance.
-- 
Arsen Arsenović

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