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Message-ID: <20151019110227.GB10551@port70.net>
Date: Mon, 19 Oct 2015 13:02:27 +0200
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com
Cc: Rich Felker <dalias@...c.org>
Subject: Re: musl mips n64 dynamic build
* Mahesh Bodapati <maheshbodapati90@...il.com> [2015-10-19 14:51:12 +0530]:
> Hi Rich,
>
> I have ported musl libraries for MIPS n64 ABI architecture and I have setup
> $gp as
>
> Crt1.s:
>
> *lui $3,%hi(%neg(%gp_rel(_start)))*
>
> * daddu
> $3,$3,$25 /* same in dlsym.s
> and pipe.s */*
>
> * daddiu $gp,$3,%lo(%neg(%gp_rel(_start)))*
>
> ld $4, %got_disp(main)($gp) # Get main() ..
>
>
>
> I didn???t setup $gp as in MIPS o32 ABI as we shouldn???t use _*gp*_disp for
> setting up $gp
>
> ???The special symbol name _gp_disp, used for relocating the calculation of gp
> on entry to a DSO in 32-bit files, is
>
> not supported in ELF-64 or in the new 32-bit ABI. Instead, these relocations
> should be composed with
>
> R_MIPS_GPREL applied to an explicit symbol for the entry point of the
> subprogram
>
>
>
> involves loading the difference between the entry
>
> address of a subprogram s and the runtime gp for establishing gp:
>
> A: lui rx, %hi(%neg(%gp_rel(s)))# load high part of diff
>
> B: daddiu rx, rx, %lo(%neg(%gp_rel(s)))# add low part
>
> C: dadd gp, t9, rx # add to entry address ???
>
>
>
> Now I am able to build dynamic n64 musl libraries and n64 dynamic
> application but it???s not showing any relocation with it
>
> and execution of application is giving errors like ???unsupported relocation
> type errors???
>
> $ objdump -R main
>
>
>
> a.out: file format elf64-tradbigmips
>
>
>
> DYNAMIC RELOCATION RECORDS (none)
>
>
>
> $ ./main
>
> Error relocating libc.so: unsupported relocation type 482431
>
> Error relocating libc.so: unsupported relocation type 482687
>
> Error relocating libc.so: unsupported relocation type 482943
>
> Error relocating libc.so: unsupported relocation type 483199
>
> ;
note that these are in libc.so, not main
and the numbers are incrementing by 256, so the last
byte is unchanged 0x7f which means R_MIPS_JUMP_SLOT
on o32 mips.
maybe libc is built to load 64bit elf but itself is
a 32bit elf?
try inspecting readelf -aW of libc.so
>
> ;
>
> ;
>
> Segmentation fault
>
>
>
> So Can you suggest how can I resolve these errors? I am thinking like
> either doing changes in do_mips_reloc(),do_relocs() functions in musl
> sources or in usage of relocations.
>
>
>
>
>
> Thank You In Advance.
>
>
>
> Thanks,
>
> Mahesh
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