[llvm] r192775 - Revert r192758 (and r192759), "MC: Better handling of tricky symbol and section names"

[Hans Wennborg]

On Wed, Oct 16, 2013 at 4:00 PM, Reid Kleckner <rnk at google.com> wrote:
> No idea.  .def is the COFF way of giving metadata about a symbol: function
> vs. data vs. section, and other things.  MC has an extra set of methods for
> emitting it.

Right, so it doesn't seem like we can get away from using .def :(

Looking at the gas source, I can see the difference in how parsing is
done for .set (done by s_set function) and .def (obj_coff_def). The
former uses read_symbol_name() which allows quotes, and the latter
uses get_symbol_end which doesn't.

Quotes are also not allowed in labels, and that's documented so I
guess it's intentional.

This means quoting these symbols doesn't work in practice.

I'll try to fix our asm parser to allow for @'s in unquoted symbol
names in COFF instead, I think that's the way to go.

 - Hans

> On Wed, Oct 16, 2013 at 3:26 PM, Hans Wennborg <hans at chromium.org> wrote:
>>
>> On Wed, Oct 16, 2013 at 3:15 PM, Rafael Espíndola
>> <rafael.espindola at gmail.com> wrote:
>> >> with gas:
>> >> 00000000 b .bss
>> >> 00000000 d .data
>> >> 00000000 t .text
>> >> 00000000 T __Z1fv
>> >>
>> >> with clang:
>> >> 00000000 t .text
>> >> 00000001 a @feat.00
>> >> 00000000 T __Z1fv
>> >>
>> >> So if gas doesn't understand the @feat.00 thing, maybe we should only
>> >> do it when targeting win32 (which means using our own assembler,
>> >> right?), thereby avoiding this whole problem?
>> >
>> > What is wrong with using ".set"? That would work with gas too.
>>
>> The file looks like this:
>>
>> .def "@feat.00";
>> .scl 3;
>> .type 0;
>> .endef
>> "@feat.00" = 1
>> .def __Z1fv;
>> .scl 2;
>> .type 32;
>> .endef
>> .text
>> .globl __Z1fv
>> .align 16, 0x90
>> __Z1fv:
>> pushl %ebp
>> movl %esp, %ebp
>> movl $5, %eax
>> popl %ebp
>> ret
>>
>> I can fix the "@feat.00" = 1 by switching to .set, but it still
>> complains about .def on line 1. I don't even know what's going on up
>> there. Reid?