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Subject[PATCH] tracing: remove superfluous sub instructions
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hi,

I think there's no need for substracting MCOUNT_INSN_SIZE from the
IP parameter before calling the function trace (/graph) handler.

Maybe I overlooked something, but all the IP usage I saw ended
up in the kallsyms_lookup function, which does the lookup using the
functions' start/end boundaries to find the correct symbol for pointer.

Thus it seems to me there's no point in substracting the
MCOUNT_INSN_SIZE value from the IP parameter.

I tested for x86_64 and got proper results, I believe it's
the same case for x86_32.

wbr,
jirka


Signed-off-by: Jiri Olsa <jolsa@redhat.com>
---
arch/x86/kernel/entry_32.S | 3 ---
arch/x86/kernel/entry_64.S | 3 ---
2 files changed, 0 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 591e601..92cdb47 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -1122,7 +1122,6 @@ ENTRY(ftrace_caller)
pushl %edx
movl 0xc(%esp), %eax
movl 0x4(%ebp), %edx
- subl $MCOUNT_INSN_SIZE, %eax

.globl ftrace_call
ftrace_call:
@@ -1168,7 +1167,6 @@ trace:
pushl %edx
movl 0xc(%esp), %eax
movl 0x4(%ebp), %edx
- subl $MCOUNT_INSN_SIZE, %eax

call *ftrace_trace_function

@@ -1191,7 +1189,6 @@ ENTRY(ftrace_graph_caller)
movl 0xc(%esp), %edx
lea 0x4(%ebp), %eax
movl (%ebp), %ecx
- subl $MCOUNT_INSN_SIZE, %edx
call prepare_ftrace_return
popl %edx
popl %ecx
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index d3b895f..662f8f6 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -75,7 +75,6 @@ ENTRY(ftrace_caller)

movq 0x38(%rsp), %rdi
movq 8(%rbp), %rsi
- subq $MCOUNT_INSN_SIZE, %rdi

GLOBAL(ftrace_call)
call ftrace_stub
@@ -115,7 +114,6 @@ trace:

movq 0x38(%rsp), %rdi
movq 8(%rbp), %rsi
- subq $MCOUNT_INSN_SIZE, %rdi

call *ftrace_trace_function

@@ -136,7 +134,6 @@ ENTRY(ftrace_graph_caller)
leaq 8(%rbp), %rdi
movq 0x38(%rsp), %rsi
movq (%rbp), %rdx
- subq $MCOUNT_INSN_SIZE, %rsi

call prepare_ftrace_return


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