musl - Re: MUSL issue while loading C++ lib

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Message-ID: <CAOkOUee5gw1uVKGT3+X+2+z+c2KZ=FJh=fcYCd3Zni7Jeer2wQ@mail.gmail.com>
Date: Wed, 27 Jan 2016 14:04:59 -0500
From: N Jain <jain61@...il.com>
To: musl@...ts.openwall.com, Szabolcs Nagy <nsz@...t70.net>
Subject: Re: MUSL issue while loading C++ lib

Hi All,

I was debugging and trying to find the issue in MUSL during finding
 "_Unwind_Resume_or_Rethrow" symbol.
I see that under find_sym function sysv_lookup(s,h,dso) function it is not
able to get above names which seems to be right as the offset in reloc
section of "libstdc++.so.6" is zero

Example table below -

Offset          Info        Type                           Sym.Value   Sym.
Name
0013700c  00000516 R_ARM_JUMP_SLOT   000c8bc8
_ZNSt13basic_filebufIcSt11char_traitsIcEE19_M_terminate_outputEv  (*Able to
lookup*)
*00137330  00051c16 R_ARM_JUMP_SLOT   00000000   _Unwind_Resume_or_Rethrow
      (Failed)*
*00137510  00083616 R_ARM_JUMP_SLOT   00000000   _Unwind_GetLanguageSpe
        (Failed)*


> > and i think the linked binary is fine
>
> > libstdc++.so.6 vs libgcc_s.so.1 has some issues
> > which makes the musl linker fail to find some symbols.
>

>From above dump I can see if Sym.Value = 0x0 then the symbol lookup fails.
Can some one know how to solve above issue ?
Also I am not able to find the code if libstdc++.so.6  needs dynamic
section libgcc_s.so.1
then by the time MUSL loads libstdc++.so.6 above symbols should not have
Sym.Value = 0x0 ?



>
> > i can't help further, you will have to debug it,
> > i'd try to look at dso->strings with gdb and why the find_sym fails
> > or recompile musl with some dprintf added,
> > or try a known working toolchain and compare against it,
> > or wait for other ideas..
>

Any one know code where if library itself is dependent on other library
where is symbol relocation happening ?
I guess the issue is in that part of MUSL code ? Is there any MUSL patch to
resolve above issue ?

Thanks,
NJ

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