Re: [PATCH v2] libc: arm: Implement setjmp GCC backwards compatibility.

[Richard Earnshaw <Richard.Earnshaw@foss.arm.com>]

On 03/02/2023 11:15, Victor L. Do Nascimento wrote:
> When compiling Newlib for arm targets with GCC 12.1 onward, the
> passing of architecture extension information to the assembler is
> automatic, making the use of .fpu and .arch_extension directives
> in assembly files redundant.
> 
> With older versions of GCC, however, these directives must be
> hard-coded into the `arm/setjmp.S' file to allow the assembly of
> instructions concerning the storage and subsequent reloading of the
> floating point registers to/from the jump buffer, respectively.
> 
> This patch conditionally adds the `.fpu vfpxd' and `.arch_extension
> mve' directives based on compile-time preprocessor macros concerning
> GCC version and target architectural features, such that both the
> assembly and linking of setjmp.S succeeds for older versions of
> Newlib.
> ---
>   newlib/libc/machine/arm/setjmp.S | 22 ++++++++++++++++++++++
>   1 file changed, 22 insertions(+)
> 
> diff --git a/newlib/libc/machine/arm/setjmp.S b/newlib/libc/machine/arm/setjmp.S
> index c615f2428..5401534cd 100644
> --- a/newlib/libc/machine/arm/setjmp.S
> +++ b/newlib/libc/machine/arm/setjmp.S
> @@ -64,6 +64,28 @@
>   
>   	.syntax unified
>   
> +/*  GCC 12.1 and later will tell the assembler exactly which floating
> +    point (or MVE) unit is required and we don't want to override
> +    that.  Conversely, older versions of the compiler don't pass this
> +    information so we need to enable the VFP version that is most
> +    appropriate.  The choice here should support all suitable VFP
> +    versions that the older toolchains can handle.  */
> +#if __GNUC__ && __GNUC__ < 12
> +/*  Ensure that FPU instructions are correctly compiled and, likewise,
> +    the appropriate build attributes are added to the resulting object
> +    file.  Check whether the MVE extension is present and whether
> +    we have support for hardware floating point-operations.  VFPxd
> +    covers all the cases we need in this file for hardware
> +    floating-point and should be compatible with all required FPUs
> +    that we need to support.  */
> +# if __ARM_FP
> +	.fpu vfpxd
> +# endif
> +# if __ARM_FEATURE_MVE
> +	.arch_extension mve
> +# endif
> +#endif
> +
>   #if __ARM_ARCH_ISA_THUMB == 1 && !__ARM_ARCH_ISA_ARM
>   /* ARMv6-M-like has to be implemented in Thumb mode.  */
>   

Thanks, pushed.