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

[Hans Wennborg]

On Wed, Oct 16, 2013 at 4:44 PM, Hans Wennborg <hans at chromium.org> wrote:
> 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.

That didn't work because of things like foo at IMGREL.

I've gone back to the quoting approach and not emitting @feat.00 on
non-win32, which means quoted symbols shouldn't be showing up on
cygwin/mingw. Committed that in r192859.

 - 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?