Messages in this thread | | | Date | Sat, 29 Feb 2020 23:58:40 +0100 | From | Stefan Agner <> | Subject | Re: [PATCH] ARM: use assembly mnemonics for VFP register access |
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On 2020-02-21 07:34, Stefan Agner wrote: > Clang's integrated assembler does not allow to to use the mcr > instruction to access floating point co-processor registers: > arch/arm/vfp/vfpmodule.c:342:2: error: invalid operand for instruction > fmxr(FPEXC, fpexc & > ~(FPEXC_EX|FPEXC_DEX|FPEXC_FP2V|FPEXC_VV|FPEXC_TRAP_MASK)); > ^ > arch/arm/vfp/vfpinstr.h:79:6: note: expanded from macro 'fmxr' > asm("mcr p10, 7, %0, " vfpreg(_vfp_) ", cr0, 0 @ fmxr " > #_vfp_ ", %0" \ > ^ > <inline asm>:1:6: note: instantiated into assembly here > mcr p10, 7, r0, cr8, cr0, 0 @ fmxr FPEXC, r0 > ^ > > The GNU assembler supports the .fpu directive at least since 2.17 (when > documentation has been added). Since Linux requires binutils 2.21 it is > safe to use .fpu directive. Use the .fpu directive and mnemonics for VFP > register access. > > This allows to build vfpmodule.c with Clang and its integrated assembler. > > Link: https://github.com/ClangBuiltLinux/linux/issues/905 > Signed-off-by: Stefan Agner <stefan@agner.ch> > --- > arch/arm/vfp/vfpinstr.h | 12 ++++-------- > 1 file changed, 4 insertions(+), 8 deletions(-) > > diff --git a/arch/arm/vfp/vfpinstr.h b/arch/arm/vfp/vfpinstr.h > index 38dc154e39ff..799ccf065406 100644 > --- a/arch/arm/vfp/vfpinstr.h > +++ b/arch/arm/vfp/vfpinstr.h > @@ -62,21 +62,17 @@ > #define FPSCR_C (1 << 29) > #define FPSCR_V (1 << 28) > > -/* > - * Since we aren't building with -mfpu=vfp, we need to code > - * these instructions using their MRC/MCR equivalents. > - */ > -#define vfpreg(_vfp_) #_vfp_ > - > #define fmrx(_vfp_) ({ \ > u32 __v; \ > - asm("mrc p10, 7, %0, " vfpreg(_vfp_) ", cr0, 0 @ fmrx %0, " #_vfp_ \ > + asm(".fpu vfpv2\n" \ > + "vmrs %0, " #_vfp_ \ > : "=r" (__v) : : "cc"); \ > __v; \ > }) > > #define fmxr(_vfp_,_var_) \ > - asm("mcr p10, 7, %0, " vfpreg(_vfp_) ", cr0, 0 @ fmxr " #_vfp_ ", %0" \ > + asm(".fpu vfpv2\n" \ > + "vmsr " #_vfp_ ", %0" \ > : : "r" (_var_) : "cc") > > u32 vfp_single_cpdo(u32 inst, u32 fpscr);
I just found out that this fails with binutils 2.23.1. Since we support binutils back to 2.21 I guess that is not OK..?
CC arch/arm/vfp/vfpmodule.o /tmp/cc2Vcw98.s: Assembler messages: /tmp/cc2Vcw98.s:920: Error: operand 1 must be a VFP extension System Register -- `vmrs r6,FPINST' /tmp/cc2Vcw98.s:948: Error: operand 1 must be a VFP extension System Register -- `vmrs r6,FPINST2'
Looking into binutils history reveals that FPINST/FPINST2 has been allowed with 16d02dc907c5717b5f47076bb90ae3795e73b59f ("gas/config/tc-arm.c (do_vmrs): Accept all control registers") which made it into binutils 2.24...
I don't have a particular good idea how to make this work for Clang and GCC other than a some ifdef's...
-- Stefan
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