Re: [Qemu-devel] [PATCH] Fix symbol lookup for mips64* targets

[Blue Swirl]

On 10/3/08, Stefan Weil <address@hidden> wrote:
> Thiemo Seufer schrieb:
>
> > Stefan Weil wrote:
>  >
>  >> For 64 bit targets, lookup_symbol() compares a 64-bit target address
>  >> with a 32 bit symbol address. This only works for addresses less than 
> 2^32.
>  >>
>  >> MIPS64 kernels use addresses larger than 0xffffffff80000000,
>  >> so qemu.log never shows symbolic names.
>  >>
>  >> My patch is a workaround which works with Qemu's 32 bit address hack.
>  >> Please apply it to Qemu trunk.
>  >>
>  >> Maybe a better solution would use symbol addresses without shortening
>  >> them to 32 bits.
>  >>
>  >> Regards
>  >> Stefan
>  >>
>  >>
>  >
>  >
>  >> Fix symbol lookup for mips64* targets.
>  >>
>  >> Signed-off-by: Stefan Weil <address@hidden>
>  >>
>  >> Index: disas.c
>  >> ===================================================================
>  >> --- disas.c  (Revision 5400)
>  >> +++ disas.c  (Arbeitskopie)
>  >> @@ -309,6 +309,11 @@
>  >>      struct syminfo *s;
>  >>      target_ulong addr;
>  >>
>  >> +#if defined(TARGET_MIPS64)
>  >> +    /* Adresses in syminfos are 32 bit values. */
>  >> +    orig_addr &= 0xffffffff;
>  >>
>  >
>  > This isn't true in general, not all MIPS64 kernels use the -msym32
>  > optimization.
>  >
>  >
>  > Thiemo
>
> Nor does my MIPS64 kernel: it uses 64 bit symbol addresses.
>
>  The current Qemu loads these addresses, reduces them to 32 bit and
>  stores the reduced 32 bit addresses. So the 32 bit addresses are made
>  by Qemu. They have nothing to do with kernel compile flags.
>
>  In lookup_symbol, Qemu compares real 64 bit addresses to the reduced
>  32 bit addresses which does not work for addresses larger than 2^32.
>  x86_64 kernels have no problem because they have small addresses.
>  MIPS64 kernels have a problem because they have large addresses.
>  I don't know whether ppc64 and sparc64 work, maybe someone who
>  has such kernels can do a "nm vmlinux".

Sparc64 kernel is located below 4G.

>  My patch is only a workaround which reduces the real 64 bit addresses
>  to 32 bit, too.
>
>  I suggest to apply it to Qemu trunk (because it is small and it improves
>  the current situation) and to add a note to the TODO list:
>  - store symbol addresses in full size (important for 64 bit targets)

We could be more ambitious and make the symbol size depend on target.
It does not look too hard.