[xen master] x86/AMD: Convert wrmsr_amd_safe() to use asm goto()

[patchbot@xxxxxxx]

commit b3d8b3e3f3aa4dcb1cf11acb90cfe368837e9534
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Thu Apr 3 15:37:23 2025 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Mon Apr 7 19:17:38 2025 +0100

    x86/AMD: Convert wrmsr_amd_safe() to use asm goto()
    
    Bloat-o-meter reports:
    
      add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-29 (-29)
      Function                                     old     new   delta
      _probe_mask_msr                               99      94      -5
      init_amd                                    2418    2394     -24
    
    but this under-reports because .fixup doesn't contain sized/typed symbols.
    This also drops two "mov -EFAULT, %reg; jmp ...;" sequences too, so the net
    saving is -50.
    
    wrmsr_amd_safe()'s return value is only checked against 0 (if at all), and
    because of this, the compiler can now avoid manifesting the 0/-EFAULT
    constants entirely, and the %[fault] label simply lands on the right basic
    block.
    
    Convert to Xen style while rewriting.
    
    No functional change.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/cpu/amd.c | 22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)

diff --git a/xen/arch/x86/cpu/amd.c b/xen/arch/x86/cpu/amd.c
index 597b0f073d..ce4e1df710 100644
--- a/xen/arch/x86/cpu/amd.c
+++ b/xen/arch/x86/cpu/amd.c
@@ -74,21 +74,19 @@ static inline int rdmsr_amd_safe(unsigned int msr, unsigned 
int *lo,
 }
 
 static inline int wrmsr_amd_safe(unsigned int msr, unsigned int lo,
-                                unsigned int hi)
+                                 unsigned int hi)
 {
-       int err;
+    asm goto ( "1: wrmsr\n\t"
+               _ASM_EXTABLE(1b, %l[fault])
+               :
+               : "c" (msr), "a" (lo), "d" (hi), "D" (0x9c5a203a)
+               :
+               : fault );
 
-       asm volatile("1: wrmsr\n2:\n"
-                    ".section .fixup,\"ax\"\n"
-                    "3: movl %6,%0\n"
-                    "   jmp 2b\n"
-                    ".previous\n"
-                    _ASM_EXTABLE(1b, 3b)
-                    : "=r" (err)
-                    : "c" (msr), "a" (lo), "d" (hi), "D" (0x9c5a203a),
-                      "0" (0), "i" (-EFAULT));
+    return 0;
 
-       return err;
+ fault:
+    return -EFAULT;
 }
 
 static void wrmsr_amd(unsigned int msr, uint64_t val)
--
generated by git-patchbot for /home/xen/git/xen.git#master