[RFC][PATCH 8/9 v2] ftrace/x86: Get rid of ftrace_caller_setup

From: Steven Rostedt
Date: Tue Nov 25 2014 - 06:51:58 EST


From: "Steven Rostedt (Red Hat)" <rostedt@xxxxxxxxxxx>

Move all the work from ftrace_caller_setup into save_mcount_regs. This
simplifies the code and makes it easier to understand.

Link: http://lkml.kernel.org/r/CA+55aFxUTUbdxpjVMW8X9c=o8sui7OB_MYPfcbJuDyfUWtNrNg@xxxxxxxxxxxxxx

Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
arch/x86/kernel/mcount_64.S | 71 +++++++++++++++++++++++++++------------------
1 file changed, 42 insertions(+), 29 deletions(-)

diff --git a/arch/x86/kernel/mcount_64.S b/arch/x86/kernel/mcount_64.S
index 003b22df1d87..ddc766efa1f1 100644
--- a/arch/x86/kernel/mcount_64.S
+++ b/arch/x86/kernel/mcount_64.S
@@ -54,7 +54,15 @@
* be saved in the locations that pt_regs has them in.
*/

-/* @added: the amount of stack added before calling this */
+/*
+ * @added: the amount of stack added before calling this
+ *
+ * After this is called, the following registers contain:
+ *
+ * %rdi - holds the address that called the trampoline
+ * %rsi - holds the parent function (traced function's return address)
+ * %rdx - holds the original %rbp
+ */
.macro save_mcount_regs added=0

/* Always save the original rbp */
@@ -101,9 +109,24 @@
movq MCOUNT_REG_SIZE-8(%rsp), %rdx
movq %rdx, RBP(%rsp)

+ /* Copy the parent address into %rsi (second parameter) */
+#ifdef CC_USING_FENTRY
+ movq MCOUNT_REG_SIZE+8+\added(%rsp), %rsi
+#else
+ /* %rdx contains original %rbp */
+ movq 8(%rdx), %rsi
+#endif
+
/* Move RIP to its proper location */
movq MCOUNT_REG_SIZE+\added(%rsp), %rdi
movq %rdi, RIP(%rsp)
+
+ /*
+ * Now %rdi (the first parameter) has the return address of
+ * where ftrace_call returns. But the callbacks expect the
+ * the address of the call itself.
+ */
+ subq $MCOUNT_INSN_SIZE, %rdi
.endm

.macro restore_mcount_regs
@@ -122,28 +145,6 @@

.endm

-/* skip is set if stack has been adjusted */
-.macro ftrace_caller_setup trace_label added=0
- save_mcount_regs \added
-
- /* Save this location */
-GLOBAL(\trace_label)
- /* Load the ftrace_ops into the 3rd parameter */
- movq function_trace_op(%rip), %rdx
-
- /* %rdi already has %rip from the save_mcount_regs macro */
- subq $MCOUNT_INSN_SIZE, %rdi
- /* Load the parent_ip into the second parameter */
-#ifdef CC_USING_FENTRY
- movq MCOUNT_REG_SIZE+8+\added(%rsp), %rsi
-#else
- /* Need to grab the original %rbp */
- movq RBP(%rsp), %rsi
- /* Now parent address is 8 above original %rbp */
- movq 8(%rsi), %rsi
-#endif
-.endm
-
#ifdef CONFIG_DYNAMIC_FTRACE

ENTRY(function_hook)
@@ -151,7 +152,13 @@ ENTRY(function_hook)
END(function_hook)

ENTRY(ftrace_caller)
- ftrace_caller_setup ftrace_caller_op_ptr
+ /* save_mcount_regs fills in first two parameters */
+ save_mcount_regs
+
+GLOBAL(ftrace_caller_op_ptr)
+ /* Load the ftrace_ops into the 3rd parameter */
+ movq function_trace_op(%rip), %rdx
+
/* regs go into 4th parameter (but make it NULL) */
movq $0, %rcx

@@ -182,7 +189,12 @@ ENTRY(ftrace_regs_caller)
pushfq

/* added 8 bytes to save flags */
- ftrace_caller_setup ftrace_regs_caller_op_ptr 8
+ save_mcount_regs 8
+ /* save_mcount_regs fills in first two parameters */
+
+GLOBAL(ftrace_regs_caller_op_ptr)
+ /* Load the ftrace_ops into the 3rd parameter */
+ movq function_trace_op(%rip), %rdx

/* Save the rest of pt_regs */
movq %r15, R15(%rsp)
@@ -263,7 +275,8 @@ GLOBAL(ftrace_stub)
retq

trace:
- ftrace_caller_setup ftrace_caller_op_ptr
+ /* save_mcount_regs fills in first two parameters */
+ save_mcount_regs

call *ftrace_trace_function

@@ -276,16 +289,16 @@ END(function_hook)

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
ENTRY(ftrace_graph_caller)
+ /* Saves rbp into %rdx */
save_mcount_regs

#ifdef CC_USING_FENTRY
leaq MCOUNT_REG_SIZE+8(%rsp), %rdi
movq $0, %rdx /* No framepointers needed */
#else
- /* Need to grab the original %rbp */
- movq RBP(%rsp), %rdx
- /* Now parent address is 8 above original %rbp */
+ /* Save address of the return address of traced function */
leaq 8(%rdx), %rdi
+ /* ftrace does sanity checks against frame pointers */
movq (%rdx), %rdx
#endif
movq RIP(%rsp), %rsi
--
2.1.1


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