[xen staging] x86: drop REX64_PREFIX

[patchbot@xxxxxxx]

commit 0e3642514719c0659f2af44b1bbe8aba63d4a2ed
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Mon Jul 22 09:39:40 2024 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Jul 22 09:39:40 2024 +0200

    x86: drop REX64_PREFIX
    
    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 older gas.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/i387.c                  | 15 ++++-----------
 xen/arch/x86/include/asm/asm_defns.h |  8 --------
 2 files changed, 4 insertions(+), 19 deletions(-)

diff --git a/xen/arch/x86/i387.c b/xen/arch/x86/i387.c
index fcdee10a6e..400c70114a 100644
--- a/xen/arch/x86/i387.c
+++ b/xen/arch/x86/i387.c
@@ -64,13 +64,12 @@ static inline void fpu_fxrstor(struct vcpu *v)
     {
     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 vcpu *v)
             ".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 vcpu *v)
 
     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
diff --git a/xen/arch/x86/include/asm/asm_defns.h 
b/xen/arch/x86/include/asm/asm_defns.h
index 0a3ff70566..92b4116a15 100644
--- 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                            ; \
--
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