Peter Tanski wrote:
On Nov 22, 2006, at 4:18 AM, Simon Marlow wrote:Peter Tanski wrote:On Nov 21, 2006, at 11:48 AM, Simon Marlow wrote:Peter Tanski wrote:I tested out the 0.5.0 build of yasm on assembler output from GHC 6.6 and yasm chokes on expressions like this: _Main_main_srt - (_Main_main_info) + 0 It gives the error "expression too complex," which I tracked to a function in the yasm source file libyasm/value.c. I am still looking into it.It's possible YASM doesn't grok these. I doubt that gcc ever generates them, which is probably why.This is an example of a complex relocation. If the two symbols are defined in the current file and are in the same section, then the offset can be computed statically by the assembler. Otherwise it has to be left as a relocation in the object file for the linker; in which case *one* of the symbols must be in the same section as the relocation, and the assembler emits a PC- relative relocation descriptor (eg. R_X86_PC32 is a 32-bit PC- relative relocation in ELF). A PC-relative relocation is of the form (current address + offset + symbol).It turns out that GNU binutils can't handle the 64-bit PC- relative relocation yet, which is why we use 32-bit relative offsets in our info tables on x86_64 (there's a small comment about this in PprMach:754).... I'm not sure where to go from here: there are two solutions. I could modify the NCG to output the correct data sections and hope Yasm picks up the reference or I could look into fixing Yasm.By "modify the NCG to output the correct data sections" do you mean putting the two symbols in the same section for a relative reference? This means putting SRTs in the text section. We used to do this (this was one workaround for the lack of 64-bit relative relocations on x86_64), but it's not really the right thing; SRTs should go in the read-only data section to avoid polluting the code cache.I meant sorting out the potential relocation symbols ourselves and put them into a '.reloc' section ('.reloc' is for COFF). This is something the assembler (Yasm) should do.
Ok, I'm out of my depth here, I don't know what the .reloc section does (or anything abot COFF, for that matter).
Cheers,
Simon
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