arm64.h: fix compile error with Clang

Clang 18.1.6 fails to compile OP-TEE OS with the following error:

   CC      out/arm/core/arch/arm/kernel/vfp.o
 In file included from core/arch/arm/kernel/vfp.c:6:
 In file included from core/arch/arm/include/arm.h:137:
 core/arch/arm/include/arm64.h:455:1: error: expected readable system register
   455 | DEFINE_U32_REG_READWRITE_FUNCS(fpcr)
       | ^
 core/arch/arm/include/arm64.h:436:3: note: expanded from macro 'DEFINE_U32_REG_READWRITE_FUNCS'
   436 |                 DEFINE_U32_REG_READ_FUNC(reg)   \
       |                 ^
 core/arch/arm/include/arm64.h:430:3: note: expanded from macro 'DEFINE_U32_REG_READ_FUNC'
   430 |                 DEFINE_REG_READ_FUNC_(reg, uint32_t, reg)
       |                 ^
 core/arch/arm/include/arm64.h:417:15: note: expanded from macro 'DEFINE_REG_READ_FUNC_'
   417 |         asm volatile("mrs %0, " #asmreg : "=r" (val64));        \
       |                      ^
 <inline asm>:1:10: note: instantiated into assembly here
     1 |         mrs x8, fpcr
       |                 ^

...and similar ones for fpcr write, as well as fpsr read and write.

Clang 12.0.0 does not have any problem with this code which makes me
think that it's a Clang/LLVM issue.

Work around the problem by using the coded system register identifiers
S3_3_c4_c4_0 and S3_3_c4_c4_1 instead of fpcr and fpsr, respectively.
The values 3-3-4-4-0 and 3-3-4-4-1 are taken from the Arm ARM sections
C.5.2.8 and C.5.2.9.

Signed-off-by: Jerome Forissier <[email protected]>
Acked-by: Joakim Bech <[email protected]>
Acked-by: Jens Wiklander <[email protected]>

core/arch/arm/include/arm64.h

@@ -452,8 +452,15 @@ static inline __noprof void write_##reg(type val)		\
 
 DEFINE_U32_REG_READWRITE_FUNCS(cpacr_el1)
 DEFINE_U32_REG_READWRITE_FUNCS(daif)
+#ifdef __clang__
+DEFINE_REG_READ_FUNC_(fpcr, uint32_t, S3_3_c4_c4_0)
+DEFINE_REG_WRITE_FUNC_(fpcr, uint32_t, S3_3_c4_c4_0)
+DEFINE_REG_READ_FUNC_(fpsr, uint32_t, S3_3_c4_c4_1)
+DEFINE_REG_WRITE_FUNC_(fpsr, uint32_t, S3_3_c4_c4_1)
+#else
 DEFINE_U32_REG_READWRITE_FUNCS(fpcr)
 DEFINE_U32_REG_READWRITE_FUNCS(fpsr)
+#endif
 
 DEFINE_U32_REG_READ_FUNC(ctr_el0)
 #define read_ctr() read_ctr_el0()