Re: [ARM] Relocations against STN_UNDEF

[Richard Henderson <rth at redhat dot com>]

On 09/24/2010 04:25 AM, Thomas Schwinge wrote:
> Hello!
> 
> The ELF standard says that STN_UNDEF (symbol index zero, the undefined
> symbol index) is to be marked as SHN_UNDEF, undefined symbol.  There is
> one exception however: during relocations processing, a relocation
> against STN_UNDEF shall be treated as a symbol value of zero.
> 
> For example on ARM, the bl instruction does a PC-relative jump, so to
> jump to an absolute value of 0x10000, ``bl 0x10000'' has to keep its
> relocation until the final linking is done, to be converted to the proper
> PC-relative offset.
> 
>     $ cat < ~/sgxx/issue8612/bl_ABS.s
>             bl 0x10000
>     $ "$PWD"_install/bin/*-as -o bl_ABS.o ~/sgxx/issue8612/bl_ABS.s
>     $ "$PWD"_install/bin/*-readelf -r bl_ABS.o 
>     
>     Relocation section '.rel.text' at offset 0x25c contains 1 entries:
>      Offset     Info    Type            Sym.Value  Sym. Name
>     00000000  0000001c R_ARM_CALL       

Err, why isn't this relocation against (the section symbol for) SHN_ABS
plus the 0x10000 offset?


r~