fix(shim-sev): syscall: use rbp instead of rbx for the stack pointer
`rbp` is commonly used to save the previous stack frame pointer and is used for stack backtrace.
@@ -58,8 +58,8 @@ pub unsafe extern "sysv64" fn _syscall_enter() -> ! {
push {USER_CODE_SEGMENT}
push rcx # push userspace return pointer
- push rbx
- mov rbx, rsp
+ push rbp
+ mov rbp, rsp
# Arguments in registers:
# SYSV: rdi, rsi, rdx, rcx, r8, r9
@@ -95,7 +95,7 @@ pub unsafe extern "sysv64" fn _syscall_enter() -> ! {
pop rsi
pop rdi
- pop rbx
+ pop rbp
xor rcx, rcx # do not leak contents to userspace
xor r11, r11 # do not leak contents to userspace
