Re: [PATCH, CFI] Fix EH for coldfire-uclinux

[Richard Henderson <rth at redhat dot com>]

On 11/03/2009 01:35 PM, Maxim Kuvyrkov wrote:
> To generate bFLT binaries for coldfire-uclinux elf2flt utility is used.
> Elf2flt does not honor PT_LOAD's from the executable. So, despite
> appearances of the ELF file, .text and .eh_frame sections will not end
> up in the same segment in bFLT file. Therefore PC-relative encoding
> cannot be used for CFI on coldfire-uclinux. Hence this patch defines
> CFI_DIFF_EXPR_OK to 0 for coldfire-uclinux.

I don't see anything wrong with the patch as far as it goes, but...

The best solution would be to fix elf2flt and get the eh data into the 
read-only section, then use DW_EH_PE_datarel for any items that reside 
in the data section.

The ideal relocation type for datarel relocations is something like 
R_386_GOTOFF.  You don't have that one on m68k (though it wouldn't be 
hard to add, and would improve all of the code generated by the compiler 
for this memory model).  What you do have is R_68K_GOT32O, which is 
DW_EH_PE_datarel|DW_EH_PE_indirect.  The only thing missing at this 
point is the fact that unlike other targets, m68k doesn't parse the 
@RELOC specifiers on .long data.

Fix that and you'll significantly reduce the number of relocations 
needed in those bFLT files.


r~