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[PATCH v2] x86: Avoid using .byte for instructions where safe to do so

To: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>

From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Date: Thu, 9 Apr 2026 12:41:51 +0100

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Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>

Delivery-date: Thu, 09 Apr 2026 11:41:58 +0000

List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

The new toolchain baseline knows XGETBV, VPXOR and VPOR. For the other cases using .byte, annotate the toolchain minima. No functional change. Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> --- CC: Jan Beulich <jbeulich@xxxxxxxx> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx> CC: Teddy Astie <teddy.astie@xxxxxxxxxx> v2 * CLZERO, {WR,RD}PKRU can't be named yet. Pull out of previous series as it's somewhat unrelated. The XSAVE cleanup has other prerequiesites before it can move away from .byte. --- xen/arch/x86/arch.mk | 4 +++ xen/arch/x86/include/asm/asm-defns.h | 1 + xen/arch/x86/include/asm/msr.h | 2 ++ xen/arch/x86/include/asm/prot-key.h | 4 +-- xen/arch/x86/include/asm/xstate.h | 3 +-- xen/arch/x86/x86_emulate/0f01.c | 2 +- xen/arch/x86/x86_emulate/x86_emulate.c | 34 ++++++++++++-------------- 7 files changed, 27 insertions(+), 23 deletions(-) diff --git a/xen/arch/x86/arch.mk b/xen/arch/x86/arch.mk index 0b42e6312fac..cd0602a79aaf 100644 --- a/xen/arch/x86/arch.mk +++ b/xen/arch/x86/arch.mk @@ -17,7 +17,11 @@ CFLAGS-$(CONFIG_CC_IS_GCC) += -malign-data=abi $(call cc-options-add,CFLAGS,CC,$(EMBEDDED_EXTRA_CFLAGS)) $(call cc-option-add,CFLAGS,CC,-Wnested-externs) $(call as-option-add,CFLAGS,CC,".equ \"x\"$(comma)1",-DHAVE_AS_QUOTED_SYM) + +# Binutils >= 2.31, Clang >= 7 $(call as-option-add,CFLAGS,CC,"movdiri %rax$(comma)(%rax)",-DHAVE_AS_MOVDIR) + +# Binutils >= 2.33, Clang >= 9 $(call as-option-add,CFLAGS,CC,"enqcmd (%rax)$(comma)%rax",-DHAVE_AS_ENQCMD) # Check to see whether the assembler supports the .nop directive. diff --git a/xen/arch/x86/include/asm/asm-defns.h b/xen/arch/x86/include/asm/asm-defns.h index 239dc3af096c..dc9b3ce272fd 100644 --- a/xen/arch/x86/include/asm/asm-defns.h +++ b/xen/arch/x86/include/asm/asm-defns.h @@ -1,5 +1,6 @@ #include <asm/page-bits.h> +/* binutils >= 2.26 or Clang >= 3.8 */ .macro clzero .byte 0x0f, 0x01, 0xfc .endm diff --git a/xen/arch/x86/include/asm/msr.h b/xen/arch/x86/include/asm/msr.h index 941a7612f4ba..1377d156f4e1 100644 --- a/xen/arch/x86/include/asm/msr.h +++ b/xen/arch/x86/include/asm/msr.h @@ -63,6 +63,8 @@ static inline void wrmsrns(uint32_t msr, uint64_t val) /* * WRMSR is 2 bytes. WRMSRNS is 3 bytes. Pad WRMSR with a redundant CS * prefix to avoid a trailing NOP. + * + * Binutils >= 2.40, Clang >= 16 */ alternative_input(".byte 0x2e; wrmsr", ".byte 0x0f,0x01,0xc6", X86_FEATURE_WRMSRNS, diff --git a/xen/arch/x86/include/asm/prot-key.h b/xen/arch/x86/include/asm/prot-key.h index 8fb15b5c32e9..e8550e0c9203 100644 --- a/xen/arch/x86/include/asm/prot-key.h +++ b/xen/arch/x86/include/asm/prot-key.h @@ -19,7 +19,7 @@ static inline uint32_t rdpkru(void) { uint32_t pkru; - asm volatile ( ".byte 0x0f,0x01,0xee" + asm volatile ( ".byte 0x0f,0x01,0xee" /* binutils >= 2.26 or Clang >= 3.8 */ : "=a" (pkru) : "c" (0) : "dx" ); return pkru; @@ -27,7 +27,7 @@ static inline uint32_t rdpkru(void) static inline void wrpkru(uint32_t pkru) { - asm volatile ( ".byte 0x0f,0x01,0xef" + asm volatile ( ".byte 0x0f,0x01,0xef" /* binutils >= 2.26 or Clang >= 3.8 */ :: "a" (pkru), "d" (0), "c" (0) ); } diff --git a/xen/arch/x86/include/asm/xstate.h b/xen/arch/x86/include/asm/xstate.h index c96d75e38b25..0519379edb57 100644 --- a/xen/arch/x86/include/asm/xstate.h +++ b/xen/arch/x86/include/asm/xstate.h @@ -118,8 +118,7 @@ static inline uint64_t xgetbv(unsigned int index) uint32_t lo, hi; ASSERT(index); /* get_xcr0() should be used instead. */ - asm volatile ( ".byte 0x0f,0x01,0xd0" /* xgetbv */ - : "=a" (lo), "=d" (hi) : "c" (index) ); + asm volatile ( "xgetbv" : "=a" (lo), "=d" (hi) : "c" (index) ); return lo | ((uint64_t)hi << 32); } diff --git a/xen/arch/x86/x86_emulate/0f01.c b/xen/arch/x86/x86_emulate/0f01.c index 4d36c7d289a5..87d338f0c74a 100644 --- a/xen/arch/x86/x86_emulate/0f01.c +++ b/xen/arch/x86/x86_emulate/0f01.c @@ -122,7 +122,7 @@ int x86emul_0f01(struct x86_emulate_state *s, { case vex_none: /* serialize */ host_and_vcpu_must_have(serialize); - asm volatile ( ".byte 0x0f, 0x01, 0xe8" ); + asm volatile ( ".byte 0x0f, 0x01, 0xe8" ); /* Binutils >= 2.34, Clang >= 11 */ break; case vex_f2: /* xsusldtrk */ vcpu_must_have(tsxldtrk); diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c b/xen/arch/x86/x86_emulate/x86_emulate.c index 11d145e17723..e58735ee9590 100644 --- a/xen/arch/x86/x86_emulate/x86_emulate.c +++ b/xen/arch/x86/x86_emulate/x86_emulate.c @@ -4748,27 +4748,25 @@ x86_emulate( */ if ( vex.l ) { - /* vpxor %xmmN, %xmmN, %xmmN */ - asm volatile ( ".byte 0xc5,0xf9,0xef,0xc0" ); - asm volatile ( ".byte 0xc5,0xf1,0xef,0xc9" ); - asm volatile ( ".byte 0xc5,0xe9,0xef,0xd2" ); - asm volatile ( ".byte 0xc5,0xe1,0xef,0xdb" ); - asm volatile ( ".byte 0xc5,0xd9,0xef,0xe4" ); - asm volatile ( ".byte 0xc5,0xd1,0xef,0xed" ); - asm volatile ( ".byte 0xc5,0xc9,0xef,0xf6" ); - asm volatile ( ".byte 0xc5,0xc1,0xef,0xff" ); + asm volatile ( "vpxor %xmm0, %xmm0, %xmm0" ); + asm volatile ( "vpxor %xmm1, %xmm1, %xmm1" ); + asm volatile ( "vpxor %xmm2, %xmm2, %xmm2" ); + asm volatile ( "vpxor %xmm3, %xmm3, %xmm3" ); + asm volatile ( "vpxor %xmm4, %xmm4, %xmm4" ); + asm volatile ( "vpxor %xmm5, %xmm5, %xmm5" ); + asm volatile ( "vpxor %xmm6, %xmm6, %xmm6" ); + asm volatile ( "vpxor %xmm7, %xmm7, %xmm7" ); } else { - /* vpor %xmmN, %xmmN, %xmmN */ - asm volatile ( ".byte 0xc5,0xf9,0xeb,0xc0" ); - asm volatile ( ".byte 0xc5,0xf1,0xeb,0xc9" ); - asm volatile ( ".byte 0xc5,0xe9,0xeb,0xd2" ); - asm volatile ( ".byte 0xc5,0xe1,0xeb,0xdb" ); - asm volatile ( ".byte 0xc5,0xd9,0xeb,0xe4" ); - asm volatile ( ".byte 0xc5,0xd1,0xeb,0xed" ); - asm volatile ( ".byte 0xc5,0xc9,0xeb,0xf6" ); - asm volatile ( ".byte 0xc5,0xc1,0xeb,0xff" ); + asm volatile ( "vpor %xmm0, %xmm0, %xmm0" ); + asm volatile ( "vpor %xmm1, %xmm1, %xmm1" ); + asm volatile ( "vpor %xmm2, %xmm2, %xmm2" ); + asm volatile ( "vpor %xmm3, %xmm3, %xmm3" ); + asm volatile ( "vpor %xmm4, %xmm4, %xmm4" ); + asm volatile ( "vpor %xmm5, %xmm5, %xmm5" ); + asm volatile ( "vpor %xmm6, %xmm6, %xmm6" ); + asm volatile ( "vpor %xmm7, %xmm7, %xmm7" ); } ASSERT(!state->simd_size); -- 2.39.5

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