[RFC][PATCH 3/5] ftrace/x86_32: Add stack frame pointer to ftrace_caller

[Steven Rostedt <rostedt@goodmis.org>]

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

The function hook ftrace_caller does not create its own stack frame, and
this causes the ftrace stack trace to miss the first function when doing
stack traces.

 # echo schedule:stacktrace > /sys/kernel/tracing/set_ftrace_filter

Before:
         <idle>-0     [002] .N..    29.865807: <stack trace>
 => cpu_startup_entry
 => start_secondary
 => startup_32_smp
           <...>-7     [001] ....    29.866509: <stack trace>
 => kthread
 => ret_from_fork
           <...>-1     [000] ....    29.865377: <stack trace>
 => poll_schedule_timeout
 => do_select
 => core_sys_select
 => SyS_select
 => do_fast_syscall_32
 => entry_SYSENTER_32

After:
          <idle>-0     [002] .N..    31.234853: <stack trace>
 => do_idle
 => cpu_startup_entry
 => start_secondary
 => startup_32_smp
           <...>-7     [003] ....    31.235140: <stack trace>
 => rcu_gp_kthread
 => kthread
 => ret_from_fork
           <...>-1819  [000] ....    31.264172: <stack trace>
 => schedule_hrtimeout_range
 => poll_schedule_timeout
 => do_sys_poll
 => SyS_ppoll
 => do_fast_syscall_32
 => entry_SYSENTER_32

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
 arch/x86/kernel/ftrace_32.S | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/ftrace_32.S b/arch/x86/kernel/ftrace_32.S
index 4ff30f31f0a5..73d61a62649d 100644
--- a/arch/x86/kernel/ftrace_32.S
+++ b/arch/x86/kernel/ftrace_32.S
@@ -17,12 +17,19 @@ ENTRY(mcount)
 END(mcount)
 
 ENTRY(ftrace_caller)
+
+	pushl %ebp
+	movl %esp, %ebp
+
 	pushl	%eax
 	pushl	%ecx
 	pushl	%edx
 	pushl	$0				/* Pass NULL as regs pointer */
-	movl	4*4(%esp), %eax
-	movl	0x4(%ebp), %edx
+	movl	5*4(%esp), %eax
+	/* Copy original ebp into %edx */
+	movl	4*4(%esp), %edx
+	/* Get the parent ip */
+	movl	0x4(%edx), %edx
 	movl	function_trace_op, %ecx
 	subl	$MCOUNT_INSN_SIZE, %eax
 
@@ -34,6 +41,7 @@ ftrace_call:
 	popl	%edx
 	popl	%ecx
 	popl	%eax
+	popl	%ebp
 .Lftrace_ret:
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 .globl ftrace_graph_call
-- 
2.10.2