x86/fpu: Get rid of CONFIG_AS_FXSAVEQ

This change “x86/fpu: Get rid of CONFIG_AS_FXSAVEQ” in Linux kernel is authored by Borislav Petkov <bp [at] suse.de> on Fri Jan 18 00:05:40 2019 +0100.

x86/fpu: Get rid of CONFIG_AS_FXSAVEQ

This was a "workaround" to probe for binutils which could generate
FXSAVEQ, apparently gas with min version 2.16. In the meantime, minimal
required gas version is 2.20 so all those workarounds for older binutils
can be dropped.

Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andy Lutomirski <luto@kernel.org>
Link: https://lkml.kernel.org/r/20190117232408.GH5023@zn.tnic

This Linux change may have been applied to various maintained Linux releases and you can find Linux releases including commit bae54dc.

There are 51 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 arch/x86/Makefile                   |  1 -
 arch/x86/include/asm/fpu/internal.h | 50 +++++--------------------------------
 2 files changed, 6 insertions(+), 45 deletions(-)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 9c5a67d..76bc4dc 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -187,7 +187,6 @@ cfi-sigframe := $(call as-instr,.cfi_startprocn.cfi_signal_framen.cfi_endproc,
 cfi-sections := $(call as-instr,.cfi_sections .debug_frame,-DCONFIG_AS_CFI_SECTIONS=1)
 
 # does binutils support specific instructions?
-asinstr := $(call as-instr,fxsaveq (%rax),-DCONFIG_AS_FXSAVEQ=1)
 asinstr += $(call as-instr,pshufb %xmm0$(comma)%xmm0,-DCONFIG_AS_SSSE3=1)
 avx_instr := $(call as-instr,vxorps %ymm0$(comma)%ymm1$(comma)%ymm2,-DCONFIG_AS_AVX=1)
 avx2_instr :=$(call as-instr,vpbroadcastb %xmm0$(comma)%ymm1,-DCONFIG_AS_AVX2=1)
diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index fa2c93c..5d536e3 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -137,37 +137,25 @@ static inline int copy_fxregs_to_user(struct fxregs_state __user *fx)
 {
 	if (IS_ENABLED(CONFIG_X86_32))
 		return user_insn(fxsave %[fx], [fx] "=m" (*fx), "m" (*fx));
-	else if (IS_ENABLED(CONFIG_AS_FXSAVEQ))
+	else
 		return user_insn(fxsaveq %[fx], [fx] "=m" (*fx), "m" (*fx));
 
-	/* See comment in copy_fxregs_to_kernel() below. */
-	return user_insn(rex64/fxsave (%[fx]), "=m" (*fx), [fx] "R" (fx));
 }
 
 static inline void copy_kernel_to_fxregs(struct fxregs_state *fx)
 {
-	if (IS_ENABLED(CONFIG_X86_32)) {
+	if (IS_ENABLED(CONFIG_X86_32))
 		kernel_insn(fxrstor %[fx], "=m" (*fx), [fx] "m" (*fx));
-	} else {
-		if (IS_ENABLED(CONFIG_AS_FXSAVEQ)) {
-			kernel_insn(fxrstorq %[fx], "=m" (*fx), [fx] "m" (*fx));
-		} else {
-			/* See comment in copy_fxregs_to_kernel() below. */
-			kernel_insn(rex64/fxrstor (%[fx]), "=m" (*fx), [fx] "R" (fx), "m" (*fx));
-		}
-	}
+	else
+		kernel_insn(fxrstorq %[fx], "=m" (*fx), [fx] "m" (*fx));
 }
 
 static inline int copy_user_to_fxregs(struct fxregs_state __user *fx)
 {
 	if (IS_ENABLED(CONFIG_X86_32))
 		return user_insn(fxrstor %[fx], "=m" (*fx), [fx] "m" (*fx));
-	else if (IS_ENABLED(CONFIG_AS_FXSAVEQ))
+	else
 		return user_insn(fxrstorq %[fx], "=m" (*fx), [fx] "m" (*fx));
-
-	/* See comment in copy_fxregs_to_kernel() below. */
-	return user_insn(rex64/fxrstor (%[fx]), "=m" (*fx), [fx] "R" (fx),
-			  "m" (*fx));
 }
 
 static inline void copy_kernel_to_fregs(struct fregs_state *fx)
@@ -184,34 +172,8 @@ static inline void copy_fxregs_to_kernel(struct fpu *fpu)
 {
 	if (IS_ENABLED(CONFIG_X86_32))
 		asm volatile( "fxsave %[fx]" : [fx] "=m" (fpu->state.fxsave));
-	else if (IS_ENABLED(CONFIG_AS_FXSAVEQ))
+	else
 		asm volatile("fxsaveq %[fx]" : [fx] "=m" (fpu->state.fxsave));
-	else {
-		/* Using "rex64; fxsave %0" is broken because, if the memory
-		 * operand uses any extended registers for addressing, a second
-		 * REX prefix will be generated (to the assembler, rex64
-		 * followed by semicolon is a separate instruction), and hence
-		 * the 64-bitness is lost.
-		 *
-		 * Using "fxsaveq %0" would be the ideal choice, but is only
-		 * supported starting with gas 2.16.
-		 *
-		 * Using, as a workaround, the properly prefixed form below
-		 * isn't accepted by any binutils version so far released,
-		 * complaining that the same type of prefix is used twice if
-		 * an extended register is needed for addressing (fix submitted
-		 * to mainline 2005-11-21).
-		 *
-		 *  asm volatile("rex64/fxsave %0" : "=m" (fpu->state.fxsave));
-		 *
-		 * This, however, we can work around by forcing the compiler to
-		 * select an addressing mode that doesn't require extended
-		 * registers.
-		 */
-		asm volatile( "rex64/fxsave (%[fx])"
-			     : "=m" (fpu->state.fxsave)
-			     : [fx] "R" (&fpu->state.fxsave));
-	}
 }
 
 /* These macros all use (%edi)/(%rdi) as the single memory argument. */

The commit for this change in Linux stable tree is bae54dc (patch).

Leave a Reply

Your email address will not be published. Required fields are marked *