[OE-core] [PATCH] musl: use a more specific fix for ARM thumb + frame pointers

[Khem Raj]

On Fri, Oct 6, 2017 at 7:12 PM, Andre McCurdy <armccurdy at gmail.com> wrote:
> When compiling for Thumb or Thumb2, frame pointers _must_ be disabled
> since the Thumb frame pointer in r7 clashes with musl's use of inline
> asm to make syscalls (where r7 is used for the syscall NR).
>
> In most cases, frame pointers will be disabled automatically due to
> the optimisation level, but appending an explicit -fomit-frame-pointer
> to CFLAGS handles cases where optimisation is set to -O0 or frame
> pointers have been enabled by -fno-omit-frame-pointer earlier in
> CFLAGS, etc.
>
> Note that this limitation applies both to gcc and clang, the only
> difference between the two being that where gcc aborts with an error
> about reusing r7, clang apparently silently generates broken code:
>
>   https://bugs.llvm.org/show_bug.cgi?id=34165
>
> Signed-off-by: Andre McCurdy <armccurdy at gmail.com>
> ---
>  meta/recipes-core/musl/musl_git.bb | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/meta/recipes-core/musl/musl_git.bb b/meta/recipes-core/musl/musl_git.bb
> index 8b6a2e3..3766501 100644
> --- a/meta/recipes-core/musl/musl_git.bb
> +++ b/meta/recipes-core/musl/musl_git.bb
> @@ -28,6 +28,16 @@ export CROSS_COMPILE="${TARGET_PREFIX}"
>
>  LDFLAGS += "-Wl,-soname,libc.so"
>
> +# When compiling for Thumb or Thumb2, frame pointers _must_ be disabled since the
> +# Thumb frame pointer in r7 clashes with musl's use of inline asm to make syscalls
> +# (where r7 is used for the syscall NR). In most cases, frame pointers will be
> +# disabled automatically due to the optimisation level, but append an explicit
> +# -fomit-frame-pointer to handle cases where optimisation is set to -O0 or frame
> +# pointers have been enabled by -fno-omit-frame-pointer earlier in CFLAGS, etc.
> +CFLAGS_append_arm = " ${@bb.utils.contains('TUNE_CCARGS', '-mthumb', '-fomit-frame-pointer', '', d)}"
> +
> +# Pending testing, this can probably be removed (fixed more specifically above
> +# by appending -fomit-frame-pointer to CFLAGS when building for Thumb).
>  ARM_INSTRUCTION_SET_toolchain-clang = "arm"

Please remove this. Then I can test the patch with clang and see if it fails

>
>  CONFIGUREOPTS = " \
> --
> 1.9.1
>
> --
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