Re: musl mips n64 dynamic build

[Szabolcs Nagy <nsz@port70.net>]

* Mahesh Bodapati <maheshbodapati90@gmail.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