Re[2]: Issue with musl and valgrind

[d.dorau@avm.de]

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"Rich Felker" <dalias@aerifal.cx> schrieb am 06.01.2020 14:56:23:
[...]
> 
> This is really a bug in valgrind, that it's relying on a mix of the
> dynamic linker and its own mechanism for interposing malloc. Either
> the interposition should not take place until after line 1913 of
> __dls3 in dynlink.c (this is what would happen if you did it via
> LD_PRELOAD without valgrind), or valgrind should do its own loading
> and relocation of vgpreload_memcheck-*.so independent of the tracee's
> dynamic linker.
> 
> On most archs, the problem does not manifest as things are setup so
> that it's safe to call free in an unrelocated context. However
> realloc is gratuitously not safe and Adélie Linux has a patch for it
> to do it like free:
> 
> 
https://code.foxkit.us/adelie/packages/blob/master/user/valgrind/realloc.patch

> 
> But on MIPS, where there are no PC-relative references and everything
> goes through the GOT, this blows up.
> 
> I'm not sure how practical it is to get valgrind to fix this upstream.
> In the either/or above, if the first course of action is taken, the
> mechanism should probably be by inserting a breakpoint (or valgrind's
> equivalent) at the main program's e_entry address and not doing the
> replacement hack until then. Alternatively, it could just rely on
> LD_PRELOAD working without trying to do additional tricks, but maybe
> they have a good reason they're not doing that.
> 
> Rich

I was not aware of this when debugging the crash, but after looking at 
additional
debug statements and valgrind code my current understanding is that 
valgrind
actually inserts

LD_PRELOAD="
/usr/lib/valgrind/vgpreload_core-mips32-linux.so:/usr/lib/valgrind/vgpreload_memcheck-mips32-linux.so"

into the environment before loading the executable to test.
(coregrind/m_initimg/initimg-linux.c:123)

425:11:32:696 --4757:1:    main Split up command line
425:11:32:696 --4757:1:    main (early_) Process Valgrind's command line 
options
425:11:32:696 --4757:1:    main Create initial image
425:11:32:712 --4757:1: initimg Loading client
425:11:32:712 --4757:1: initimg Setup client env
425:11:32:712 --4757:2: initimg   preload_string:
425:11:32:728 --4757:2: initimg 
"/usr/lib/valgrind/vgpreload_core-mips32-linux.so:/usr/lib/valgrind/vgpreload_memcheck-mips32-linux.so"
425:11:32:728 --4757:1: initimg Setup client stack: size will be 1048576


Is my understanding correct that you would expect it to not run into
the crash I described earlier then?


Daniel

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