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

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

[Victor L. Do Nascimento]

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.  */
 
-- 
2.36.1

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

[Richard Earnshaw]

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.