Command line option `-mno-strict-align` valid for C input but not valid for object input?

[sh1boot]

No problem with this:

$ clang-19 --target=riscv64-linux-gnu -march=rv64gcv -mno-strict-align test.c

But if you compile it and then try to pass the object file it becomes a problem:

$ clang-19 --target=riscv64-linux-gnu -march=rv64gcv -mno-strict-align test.o
clang-19: error: unsupported option '-mno-strict-align' for target 'riscv64-linux-gnu'

The same thing happens with --target=aarch64-linux-gnu.

And some build tools seem to like mixing CFLAGS in on top of LDFLAGS to make this a serious impediment.

Curiously, for -munaligned-access RISC-V seems to have this problem the other way around, where it's only accepted with object files; while aarch64 has no problem with that switch in either case.

[topperc]

CC: @MaskRay @preames

[topperc]

I would hope the object file input would just give an unused option warning rather than an error.

[sh1boot]

Even a warning would be a headache for build systems where -Werror is in use. -O3 isn't a warning, for example, even though the linker (other than an LTO one) isn't going to use that to make further changes to the compiled code.

[MaskRay]

Thanks for the report. I'll add m_Group to -mstrict-align to fix the false positive when only linking is performed.

[llvmbot]

@llvm/issue-subscribers-clang-driver

Author: S H (sh1boot)

No problem with this: ``` $ clang-19 --target=riscv64-linux-gnu -march=rv64gcv -mno-strict-align test.c ```

But if you compile it and then try to pass the object file it becomes a problem:

$ clang-19 --target=riscv64-linux-gnu -march=rv64gcv -mno-strict-align test.o
clang-19: error: unsupported option '-mno-strict-align' for target 'riscv64-linux-gnu'

The same thing happens with --target=aarch64-linux-gnu.

And some build tools seem to like mixing CFLAGS in on top of LDFLAGS to make this a serious impediment.

Curiously, for -munaligned-access RISC-V seems to have this problem the other way around, where it's only accepted with object files; while aarch64 has no problem with that switch in either case.