Re: musl mips n64 dynamic build

[Mahesh Bodapati <maheshbodapati90@gmail.com>]

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Hi Rich,
Thanks for Your mail
I have ported musl for mips64 arch from porting guide.the list
includes crt_arch.h
and Now I didn't place crt assembly files for mips64 arch.

> That produces a relocation in the elf32 encoding, because I just
> assumes mips is elf32 when I wrote it. I believe the 64-bit version
> should be:
>
>        rel[1] = sym-p->syms << 32 | R_MIPS_JUMP_SLOT;

this change resolved some of the relocation type errors but still i am
getting some relocation type errors.I think these errors are from do_relocs
()
Error relocating libc.so: unsupported relocation type 4611
Error relocating libc.so: unsupported relocation type 4611
Error relocating libc.so: unsupported relocation type 4611
Error relocating libc.so: unsupported relocation type 4611
Error relocating libc.so: unsupported relocation type 4611
Error relocating libc.so: unsupported relocation type 4611
;
;
Error relocating libc.so: unsupported relocation type 4611

the relocation type value is 4611 for all the errors.

> Did you make a reloc.h defining the relocation types needed for mips
> n64 and mapping them to the generic-reloc names musl uses for them?
> See the existing arch/*/reloc.h files. Without these being defined
> directly the dynamic linker will not be able to process the
> relocations it finds in itself or in the main program or other
> libraries

I have ported reloc.h for mips64 as

*bash-3.2$ cat arch/mips64/reloc.h*
#include <endian.h>

#if __BYTE_ORDER == __LITTLE_ENDIAN
#define ENDIAN_SUFFIX "el"
#else
#define ENDIAN_SUFFIX ""
#endif

#ifdef __mips64_soft_float
#define FP_SUFFIX "-sf"
#else
#define FP_SUFFIX ""
#endif

#define LDSO_ARCH "mips64" ENDIAN_SUFFIX FP_SUFFIX

#define TPOFF_K (-0x7000)

*#define REL_SYM_OR_REL  R_MIPS_64         /*I didn't see R_MIPS_REL64  so
It is a composition of R_MIPS_64 and R_MIPS_REL relocations but i didn't
see R_MIPS_REL in elf.h. *
*
 how can i define REL_SYM_OR_REL for mips n64 abi   */*
#define REL_PLT         R_MIPS_JUMP_SLOT
#define REL_COPY        R_MIPS_COPY
#define REL_DTPMOD      R_MIPS_TLS_DTPMOD64
#define REL_DTPOFF      R_MIPS_TLS_DTPREL64
#define REL_TPOFF       R_MIPS_TLS_TPREL64
;
;
#define CRTJMP(pc,sp) __asm__ __volatile__( \
 "move $sp,%1 ; jr %0" : : "r"(pc), "r"(sp) : "memory" ) /* JR Rs  means
jump register PC <- Rs ,jump to the address in the rs*/

#define GETFUNCSYM(fp, sym, got) __asm__ ( \
 ".hidden " #sym "\n" \
 ".set push \n" \
 ".set noreorder \n" \
 " bal 1f \n" \
 "  nop \n" \
 " .gpdword . \n" \
 " .gpdword " #sym " \n" \
 "1:  ld %0, ($ra) \n" \
 " dsubu %0, $ra, %0 \n" \
 " ld $ra, 8($ra) \n" \
 " daddu %0, %0, $ra \n" \
 ".set pop \n" \
 : "=r"(*(fp)) : : "memory", "ra" )




Thanks,
Mahesh


On Mon, Oct 19, 2015 at 8:48 PM, Rich Felker <dalias@libc.org> wrote:

> On Mon, Oct 19, 2015 at 02:51:12PM +0530, Mahesh Bodapati wrote:
> > Hi Rich,
> >
> > I have ported musl libraries for MIPS n64 ABI architecture and I have
> setup
> > $gp as
> >
> > Crt1.s:
>
> crt1.s is obsolete and should not be used for new archs. The benefit
> to you is that crt_arch.h (the new way of doing it) is a lot easier to
> write. All you need to do is jump to the C entry point _start_c with
> the right calling convention for a C function and the first 2 argument
> slots containing the original stack pointer and a pointer to _DYNAMIC,
> respectively. _start_c can be assumed to be defined in the same source
> file.
>
> > *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() ..
>
> Jumping to main from crt1 is not valid. You need to call
> __libc_start_main. But if you use crt_arch.h this part happens
> automatically for you.
>
> > 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
>
> I'm not sure what document you're quoting, but sometimes these things
> express assumptions about a particular usage case that don't apply to
> what musl is doing. But you should be able to avoid writing this code
> anyway.
>
> > 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”
>
> Did you make a reloc.h defining the relocation types needed for mips
> n64 and mapping them to the generic-reloc names musl uses for them?
> See the existing arch/*/reloc.h files. Without these being defined
> directly the dynamic linker will not be able to process the
> relocations it finds in itself or in the main program or other
> libraries.
>
> But without a working crt_arch.h I'm surprised the dynamic linker can
> even start at all. Are you sure you're not using the mips32 dynamic
> linker? Look at the program headers (using readelf -l) for INTERP.
>
> > $ 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
> >
> > ;
> >
> > ;
> >
> > ;
> >
> > 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.
>
> OK, I see what's going wrong here. The invalid relocation types are
> being produced by this line in do_mips_relocs:
>
>         rel[1] = sym-p->syms << 8 | R_MIPS_JUMP_SLOT;
>
> That produces a relocation in the elf32 encoding, because I just
> assumes mips is elf32 when I wrote it. I believe the 64-bit version
> should be:
>
>         rel[1] = sym-p->syms << 32 | R_MIPS_JUMP_SLOT;
>
> Try just making that change and see if it works. If so we can work on
> making a clean conditional for 32- vs 64-bit here later.
>
> Rich
>

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