[kvm-unit-tests PATCH 1/2] x86: replace `push` `pop` with callee-clobbered list

["SU Hang" <darcy.sh@antgroup.com>]

Stopping mess up asm callee-clobbered list with `push` `pop`,
clean up code to make it more readable.

Signed-off-by: SU Hang <darcy.sh@antgroup.com>
---
 lib/x86/usermode.c | 22 +---------------------
 1 file changed, 1 insertion(+), 21 deletions(-)

diff --git a/lib/x86/usermode.c b/lib/x86/usermode.c
index e22fb8f..477cb9f 100644
--- a/lib/x86/usermode.c
+++ b/lib/x86/usermode.c
@@ -66,32 +66,12 @@ uint64_t run_in_user(usermode_func func, unsigned int fault_vector,
 			"iretq\n"
 
 			"user_mode:\n\t"
-			/* Back up registers before invoking func */
-			"push %%rbx\n\t"
-			"push %%rcx\n\t"
-			"push %%rdx\n\t"
-			"push %%r8\n\t"
-			"push %%r9\n\t"
-			"push %%r10\n\t"
-			"push %%r11\n\t"
-			"push %%rdi\n\t"
-			"push %%rsi\n\t"
 			/* Call user mode function */
 			"mov %[arg1], %%rdi\n\t"
 			"mov %[arg2], %%rsi\n\t"
 			"mov %[arg3], %%rdx\n\t"
 			"mov %[arg4], %%rcx\n\t"
 			"call *%[func]\n\t"
-			/* Restore registers */
-			"pop %%rsi\n\t"
-			"pop %%rdi\n\t"
-			"pop %%r11\n\t"
-			"pop %%r10\n\t"
-			"pop %%r9\n\t"
-			"pop %%r8\n\t"
-			"pop %%rdx\n\t"
-			"pop %%rcx\n\t"
-			"pop %%rbx\n\t"
 			/* Return to kernel via system call */
 			"int %[kernel_entry_vector]\n\t"
 			/* Kernel Mode */
@@ -112,7 +92,7 @@ uint64_t run_in_user(usermode_func func, unsigned int fault_vector,
 					sizeof(user_stack)),
 			[kernel_entry_vector]"i"(RET_TO_KERNEL_IRQ)
 			:
-			"rsi", "rdi", "rcx", "rdx");
+			"rsi", "rdi", "rbx", "rcx", "rdx", "r8", "r9", "r10", "r11");
 
 	return rax;
 }
-- 
2.32.0.3.g01195cf9f