[RFC][PATCH 4/7] ftrace/x86: Have save_mcount_regs store RIP in %rdi for first parameter

Steven Rostedt
2014-11-25T00:44:16Z

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From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

Instead of having save_mcount_regs store the RIP in %rdx as a temp register
to place it in the proper location of the pt_regs on the stack. Use the
%rdi register as the temp register. This lets us remove the extra store
in the ftrace_caller_setup macro.

Link: http://lkml.kernel.org/r/CA+55aFwF+qCGSKdGaEgW4p6N65GZ5_XTV=1NbtWDvxnd5yYLiw@mail.gmail.com

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
arch/x86/kernel/mcount_64.S | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/mcount_64.S b/arch/x86/kernel/mcount_64.S
index 0a693d011980..4f1b27642495 100644
--- a/arch/x86/kernel/mcount_64.S
+++ b/arch/x86/kernel/mcount_64.S
@@ -51,8 +51,8 @@
movq %r8, R8(%rsp)
movq %r9, R9(%rsp)
/* Move RIP to its proper location */
- movq SS+8(%rsp), %rdx
- movq %rdx, RIP(%rsp)
+ movq SS+8(%rsp), %rdi
+ movq %rdi, RIP(%rsp)
.endm

.macro restore_mcount_regs skip=0
@@ -75,8 +75,7 @@ GLOBAL(\trace_label)
/* Load the ftrace_ops into the 3rd parameter */
movq function_trace_op(%rip), %rdx

- /* Load ip into the first parameter */
- movq RIP(%rsp), %rdi
+ /* %rdi already has %rip from the save_mcount_regs macro */
subq $MCOUNT_INSN_SIZE, %rdi
/* Load the parent_ip into the second parameter */