Hi Ying,
On Tue, May 16, 2023 at 02:38:45PM +0800, Ying Huang wrote:
> 在 2023/5/9 23:15, Mark Wielaard 写道:
> > On Tue, 2023-04-11 at 16:12 +0800, Ying Huang wrote:
> >> In mips64 little-endian, r_info consists of four byte fields(contains
> >> three reloc types) and a 32-bit symbol index. In order to adapt
> >> GELF_R_SYM and GELF_R_TYPE, need convert raw data to get correct symbol
> >> index and type.
> > Is there a spec that describes this?
>
>
> references:
>
> https://www.linux-mips.org/pub/linux/mips/doc/ABI/elf64-2.4.pdf
>
> Page40 && Page41
Thanks. Interesting. If possible please include this URL in a comment.
> > I see you adjusted elf.h to include:
> >
> > +#define ELF64_MIPS_R_TYPE(i) ((i) & 0xff)
> > +#define ELF64_MIPS_R_TYPE2(i) (((i) >> 8) & 0xff)
> > +#define ELF64_MIPS_R_TYPE3(i) (((i) >> 16) & 0xff)
> >
> > And various new relocation types for MIPS variants.
> > Our elf.h comes from the glibc project. Have you also submitted these
> > changes to libc-al...@sourceware.org ?
> Has submitted.
>
> https://sourceware.org/pipermail/libc-alpha/2023-May/148026.html
>
> https://sourceware.org/pipermail/libc-alpha/2023-May/148112.html
Thanks. We'll sync them as soon as v3 lands.
> Has tested on big/little endian machine with big/little endian
> ELF file, all were OK.
Could you post those ELF files somewhere?
Maybe we can add some as test files?
> > It feels like this is in the wrong place and doesn't take into account
> > whether the program itself is running on a big or little endian
> > machine.
> >
> > Maybe I am misunderstanding why this conversion is needed always. But I
> > would have expected a specific conversion function for MIPS for
> > ELF_T_REL and/or ELF_T_RELA (which are currently generic).
>
> 1.Considering that some people directly use the original data instead of
> the interface function gelf_getrela;
>
> 2.Because there is only one parameter, so can not modify the macro
> ELF64_R_TYPE；
>
> 3.If the mips interface function is added, other packages using libelf
> will not be compatible with mips, and the place where gelf_getrela is used
> need be modified.
>
> Where do you think is the most suitable place to do mips conversion?
So for the convert_data case in elf_getdata.c I would expect a special
conversion function being defined for ELF_T_REL and ELF_T_RELA. This
normally comes from __elf_xfctstom. I realize now that cannot easily
take an Elf of machine type. But I would expect to have the conversion
be done by a new function that can be assigned to fp in convert_data:
/* Get the conversion function. */
fp = __elf_xfctstom[eclass - 1][type];
I still don't fully understand the need of the code in elf_update. I
assume that is needed in case the file was used with ELF_C_RDWR_MMAP?
Cheers,
Mark
