diff --git a/common/usermode.c b/common/usermode.c
index ecc254f1..c510688b 100644
--- a/common/usermode.c
+++ b/common/usermode.c
@@ -49,12 +49,7 @@ static inline void syscall_restore(void) {
 }
 
 static inline long syscall_return(long return_code) {
-    /* clang-format off */
-    asm volatile(
-            "mov %[ret], %%" STR(_ASM_AX) "\n"
-            ::[ret] "r"(return_code)
-    );
-    /* clang-format on */
+    asm volatile("" ::"a"(return_code));
     return return_code;
 }
 
diff --git a/include/arch/x86/asm-macros.h b/include/arch/x86/asm-macros.h
index e04d0007..e1f7f2ef 100644
--- a/include/arch/x86/asm-macros.h
+++ b/include/arch/x86/asm-macros.h
@@ -266,15 +266,23 @@ name ## _end:
         "push %%r9\n"           \
         "push %%r10\n"          \
         "push %%r11\n"          \
+        "push %%r12\n"          \
+        "push %%r13\n"          \
+        "push %%r14\n"          \
+        "push %%r15\n"          \
     ::: "memory")
 
 #define RESTORE_CLOBBERED_REGS64() \
     asm volatile (                 \
+        "pop %%" STR(r15) "\n"     \
+        "pop %%" STR(r14) "\n"     \
+        "pop %%" STR(r13) "\n"     \
+        "pop %%" STR(r12) "\n"     \
         "pop %%" STR(r11) "\n"     \
         "pop %%" STR(r10) "\n"     \
         "pop %%" STR(r9) "\n"      \
         "pop %%" STR(r8) "\n"      \
-    ::: "r8", "r9", "r10", "r11")
+    ::: "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15")
 #else
 #define SAVE_CLOBBERED_REGS64()
 #define RESTORE_CLOBBERED_REGS64()
@@ -286,18 +294,20 @@ name ## _end:
         "push %%" STR(_ASM_DX) "\n" \
         "push %%" STR(_ASM_SI) "\n" \
         "push %%" STR(_ASM_DI) "\n" \
+        "push %%" STR(_ASM_BP) "\n" \
     ::: "memory");                  \
     SAVE_CLOBBERED_REGS64()
 
 #define RESTORE_CLOBBERED_REGS()    \
     RESTORE_CLOBBERED_REGS64();     \
     asm volatile (                  \
+        "pop %%" STR(_ASM_BP) "\n"  \
         "pop %%" STR(_ASM_DI) "\n"  \
         "pop %%" STR(_ASM_SI) "\n"  \
         "pop %%" STR(_ASM_DX) "\n"  \
         "pop %%" STR(_ASM_CX) "\n"  \
-    ::: STR(_ASM_DI), STR(_ASM_SI), \
-        STR(_ASM_DX), STR(_ASM_CX))
+    ::: STR(_ASM_BP), STR(_ASM_DI), \
+    STR(_ASM_SI), STR(_ASM_DX), STR(_ASM_CX))
 /* clang-format on */
 
 #if defined(__x86_64__)