[llvm-dev] RFC: [MC] Calculate difference of symbols in two consecutive MCDataFragments

Reid Kleckner via llvm-dev llvm-dev at lists.llvm.org
Tue Nov 5 13:19:55 PST 2019


I think you meant to link to this patch here:
https://reviews.llvm.org/D69411

There's too much discussion for me to read and understand, but I think what
would help the most is developing a clear summary of what the gnu
assembler's behavior is. Do they defer evaluation of the if condition? Do
they under or overestimate offsets in the ambiguous cases? Or do they just
error out cases where there are relaxable fragments between labels? That
should help us pick a more general direction for this feature.

On Tue, Nov 5, 2019 at 12:08 PM Jian Cai via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hello,
>
> I've been trying to add support to the integrated assembler to handle
> cases like below
>
> foo:instr; .if . - foo; instr; .endif
>
> when the dot symbol and foo are assigned to consecutive MCDataFragments
> <https://github.com/ClangBuiltLinux/linux/issues/744>. I have a patch
> <https://reviews.llvm.org/D6941> under review. And even though it seems
> to solve the problem, the concern is it complicates the code and we would
> like to know if there is more decent way to handle this. Please feel free
> to share your thoughts.
>
> Thanks,
> Jian
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