On Wed, Nov 18, 2020 at 1:04 PM Jakub Jelinek via Gcc-patches <gcc-patches@gcc.gnu.org> wrote: > > On Wed, Nov 18, 2020 at 12:51:02PM +0100, Tobias Burnus wrote: > > As noted by Matthias when bootstrapping with AMD GCN support [PR97827]: > > Assembler source code generated by GCC might no longer assembly with > > LLVM's 'mc' since LLVM 11. > > > > The reason is that GCC generates on purpose first the section with > > the flags, e.g. (via mergeable_constant_section) > > .section .rodata.cst8,"aM",@progbits,8 > > and then for subsequent uses, it does not repeat the flags: > > .section .rodata.cst8 > > > > GNU assembler warns (and with as >=2.35 gives an error) if the flags > > do not match, but not if the attributes/flags are left in the other > > same-named sections (as above) – just if they are specified and different. > > > > LLVM since February (in git) and released with LLVM 11 (12 Oct 2020) > > does a similar check – but without the no-error-if-no-flag exception: > > strtod.s:4472:2: error: changed section flags for .rodata.cst8, expected: > > 0x12 > > strtod.s:4472:2: error: changed section entsize for .rodata.cst8, > > expected: 8 > > > > > > The solution done by the attached patch is to emit the full flags also > > for SECTION_MERGE. > > > > Side note: For AMD GCN, we rely on LLVM as "GNU as" does not handle > > this target, yet; still, also in general, it makes sense to be > > compatible with llvm-mc. > > > > OK? > > I think we shouldn't do this except when targetting the (buggy) llvm > assembler. > Specifying section flags just on first .section directive and not others > is correct, there is no point repeating that and GNU as (but I think many > other assemblers) has been supporting it that way forever. > The only time one needs to specify the section flags again is for comdat > sections because then the section name is not unique, one needs section name > and comdat pair...
The branch might need similar updates. Richard. > > Jakub >
