On Tue, Sep 28, 2021 at 7:10 PM Nick Desaulniers
[off-list ref] wrote:

On Tue, Sep 28, 2021 at 8:42 AM Arnd Bergmann [off-list ref] wrote:

quoted

From: Nick Desaulniers <redacted>

Similar to commit a6c30873ee4a ("ARM: 8989/1: use .fpu assembler
directives instead of assembler arguments").

GCC and GNU binutils support setting the "sub arch" via -march=,
-Wa,-march, target function attribute, and .arch assembler directive.

Clang's integrated assembler does not support -Wa,-march (and the logic
to overrule one when multiple of the above are used), and this can
cause annoying warnings such as:

clang: warning: argument unused during compilation: '-march=armv6k' [-Wunused-command-line-argument]
clang: warning: argument unused during compilation: '-march=armv6k' [-Wunused-command-line-argument]
clang: warning: argument unused during compilation: '-march=armv6k' [-Wunused-command-line-argument]

Note, the above lack of support was fixed in clang-13. That said, both
Clang and GCC defer to -Wa,-march when -march is also present, so
clang is still correct that -march is ignored.  Thanks for resending;
this is still helpful for earlier releases of clang that we still
support.

The -Wunused-command-line-argument warning also caused a build
failure for me when building with 'make W=1', and I think there are
cases where the flags from the command line are contradictory.

Isn't the patch also needed for LTO? All I know is that with this
applied it all builds, but without it I run into link failures. I can dig
more into the specific failures, but overall I think this is the right
thing to do anyway.

       Arnd

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