[musl] [PATCH] Add additional __ARM_FP checks to ARM FPU math functions

[musl] [PATCH] Add additional __ARM_FP checks to ARM FPU math functions

[Jesse DeGuire]

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Hi everyone!

I found that I was getting compiler errors when I try to build Musl
for an ARMv8.1M Mainline target that does not have floating-point
support but does have the M-Profile Vector Extensions (MVE). The
errors were that Musl wanted to use unsupported floating-point
instructions for fabsf() and sqrtf().

I was able to correct this by adding checks for (__ARM_FP & 4) to the
ARM "fabsf.c" and "sqrtf.c" files, which is all this tiny patch does.

The relevant options I used with Clang were "-march=armv8.1m.main+mve
-mfpu=none -mfloat-abi=hard". MVE uses the FP register file, but
treats them as 8 128-bit registers instead of 16 64-bit registers, so
presumably that's why the hard float ABI is used even when
floating-point operations are not enabled. In this case, an
integer-only subset of MVE is used.

Here is a Godbolt link that shows that you can make this happen on GCC, too.
https://www.godbolt.org/z/Mf4h489s8

I'm not sure if this is totally necessary since I suspect this would
affect only ARM M-Profile devices, but maybe it at least wouldn't hurt
to have.

Thanks,
Jesse DeGuire

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diff --git a/src/math/arm/fabsf.c b/src/math/arm/fabsf.c
index 4a217c98..790d4cfe 100644
--- a/src/math/arm/fabsf.c
+++ b/src/math/arm/fabsf.c
@@ -1,6 +1,6 @@
 #include <math.h>
 
-#if __ARM_PCS_VFP && !BROKEN_VFP_ASM
+#if __ARM_PCS_VFP && !BROKEN_VFP_ASM && (__ARM_FP&4)
 
 float fabsf(float x)
 {
diff --git a/src/math/arm/sqrtf.c b/src/math/arm/sqrtf.c
index 32693293..51f44f8c 100644
--- a/src/math/arm/sqrtf.c
+++ b/src/math/arm/sqrtf.c
@@ -1,6 +1,6 @@
 #include <math.h>
 
-#if (__ARM_PCS_VFP || (__VFP_FP__ && !__SOFTFP__)) && !BROKEN_VFP_ASM
+#if (__ARM_PCS_VFP || (__VFP_FP__ && !__SOFTFP__)) && !BROKEN_VFP_ASM && (__ARM_FP&4)
 
 float sqrtf(float x)
 {