aboutsummaryrefslogtreecommitdiff
path: root/sys/amd64/amd64/exception.S
diff options
context:
space:
mode:
Diffstat (limited to 'sys/amd64/amd64/exception.S')
-rw-r--r--sys/amd64/amd64/exception.S9
1 files changed, 8 insertions, 1 deletions
diff --git a/sys/amd64/amd64/exception.S b/sys/amd64/amd64/exception.S
index 08948c0904e0..c49547d8fa66 100644
--- a/sys/amd64/amd64/exception.S
+++ b/sys/amd64/amd64/exception.S
@@ -463,8 +463,16 @@ fast_syscall_common:
movq PCPU(SCRATCH_RSP),%r11 /* %r11 already saved */
movq %r11,TF_RSP(%rsp) /* user stack pointer */
movq PCPU(SCRATCH_RAX),%rax
+ /*
+ * Save a few arg registers early to free them for use in
+ * handle_ibrs_entry(). %r10 is especially tricky. It is not an
+ * arg register, but it holds the arg register %rcx. Profiling
+ * preserves %rcx, but may clobber %r10. Profiling may also
+ * clobber %r11, but %r11 (original %eflags) has been saved.
+ */
movq %rax,TF_RAX(%rsp) /* syscall number */
movq %rdx,TF_RDX(%rsp) /* arg 3 */
+ movq %r10,TF_RCX(%rsp) /* arg 4 */
SAVE_SEGS
call handle_ibrs_entry
movq PCPU(CURPCB),%r11
@@ -475,7 +483,6 @@ fast_syscall_common:
movq $2,TF_ERR(%rsp)
movq %rdi,TF_RDI(%rsp) /* arg 1 */
movq %rsi,TF_RSI(%rsp) /* arg 2 */
- movq %r10,TF_RCX(%rsp) /* arg 4 */
movq %r8,TF_R8(%rsp) /* arg 5 */
movq %r9,TF_R9(%rsp) /* arg 6 */
movq %rbx,TF_RBX(%rsp) /* C preserved */