On Tue, 2 Feb 2021, Michael Weiser wrote:
clang does not, however, support the .arch_extension directive. 3.9.1 complains
about the directive, 11.0.0 seems to silently ignore it:
$ cat t.s
.arch_extension crypto
pmull v2.1q, v2.1d, v1.1d
$ aarch64-unknown-linux-gnu-as -o t.o t.s
$ clang+llvm-3.9.1-aarch64-linux-gnu/bin/clang -c -o t.o t.s
t.s:1:1: error: unknown directive
.arch_extension crypto
^
t.s:2:1: error: instruction requires: crypto
pmull v2.1q, v2.1d, v1.1d
^
$ clang+llvm-11.0.0-aarch64-linux-gnu/bin/clang -c -o t.o t.s
t.s:2:1: error: instruction requires: aes
pmull v2.1q, v2.1d, v1.1d
^
Clang does actually support .arch_extension for aarch64 in general since
Clang 8 - but the "crypto" extension seems to be a bit of a special case,
as it expands to a number of other features, including aes and sha2,
depending on the base architecture level:
https://github.com/llvm/llvm-project/blob/main/llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp#L5361-L5388
This routine is called when enabling extensions in .arch, but not in
.arch_extension - which is a bug.
So ".arch_extension aes" would work, but setting the extension via the
.arch directive is indeed more compatible.
// Martin
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