While we didn't copy the full Linux commentary, Linux commit
7180d4fb8308 ("x86_64: Fix 64bit FXSAVE encoding") is quite explicit
about gas 2.16 supporting FXSAVEQ / FXRSTORQ. As that's presently our
minimal required version, we can drop the workaround that was needed for
yet for older gas.Signed-off-by: Jan Beulich <[email protected]> --- a/xen/arch/x86/i387.c +++ b/xen/arch/x86/i387.c @@ -64,13 +64,12 @@ static inline void fpu_fxrstor(struct vc { default: asm volatile ( - /* See below for why the operands/constraints are this way. */ - "1: " REX64_PREFIX "fxrstor (%2)\n" + "1: fxrstorq %0\n" ".section .fixup,\"ax\" \n" "2: push %%"__OP"ax \n" " push %%"__OP"cx \n" " push %%"__OP"di \n" - " mov %2,%%"__OP"di \n" + " lea %0,%%"__OP"di \n" " mov %1,%%ecx \n" " xor %%eax,%%eax \n" " rep ; stosl \n" @@ -81,7 +80,7 @@ static inline void fpu_fxrstor(struct vc ".previous \n" _ASM_EXTABLE(1b, 2b) : - : "m" (*fpu_ctxt), "i" (sizeof(*fpu_ctxt) / 4), "R" (fpu_ctxt) ); + : "m" (*fpu_ctxt), "i" (sizeof(*fpu_ctxt) / 4) ); break; case 4: case 2: asm volatile ( @@ -157,13 +156,7 @@ static inline void fpu_fxsave(struct vcp if ( fip_width != 4 ) { - /* - * The only way to force fxsaveq on a wide range of gas versions. - * On older versions the rex64 prefix works only if we force an - * addressing mode that doesn't require extended registers. - */ - asm volatile ( REX64_PREFIX "fxsave (%1)" - : "=m" (*fpu_ctxt) : "R" (fpu_ctxt) ); + asm volatile ( "fxsaveq %0" : "=m" (*fpu_ctxt) ); /* * Some CPUs don't save/restore FDP/FIP/FOP unless an exception is --- a/xen/arch/x86/include/asm/asm_defns.h +++ b/xen/arch/x86/include/asm/asm_defns.h @@ -331,14 +331,6 @@ static always_inline void stac(void) #define safe_swapgs \ "mfence; swapgs;" -#ifdef __sun__ -#define REX64_PREFIX "rex64\\" -#elif defined(__clang__) -#define REX64_PREFIX ".byte 0x48; " -#else -#define REX64_PREFIX "rex64/" -#endif - #define ELFNOTE(name, type, desc) \ .pushsection .note.name, "a", @note ; \ .p2align 2 ; \
