From: Borislav Petkov <bp@xxxxxxx>
History lesson courtesy of Steve:
"When ftrace first was introduced to the kernel, it used gcc's
mcount profiling mechanism. The mcount mechanism would add a call to
"mcount" at the start of every function but after the stack frame was
set up. Later, in gcc 4.6, gcc introduced -mfentry, that would create a
call to "__fentry__" instead of "mcount", before the stack frame was
set up. In order to handle both cases, ftrace defined a macro
"function_hook" that would be either "mcount" or "__fentry__" depending
on which one was being used.
The Linux kernel no longer supports the "mcount" method, thus there's
no reason to keep the "function_hook" define around. Simply use
"__fentry__", as there is no ambiguity to the name anymore."
Drop it everywhere.
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Acked-by: Jiri Slaby <jslaby@xxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: linux-doc@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: x86@xxxxxxxxxx
---
Documentation/asm-annotations.rst | 4 ++--
arch/x86/kernel/ftrace_32.S | 8 +++-----
arch/x86/kernel/ftrace_64.S | 13 ++++++-------
3 files changed, 11 insertions(+), 14 deletions(-)
diff --git a/Documentation/asm-annotations.rst b/Documentation/asm-annotations.rst
index 29ccd6e61fe5..f55c2bb74d00 100644
--- a/Documentation/asm-annotations.rst
+++ b/Documentation/asm-annotations.rst
@@ -117,9 +117,9 @@ This section covers ``SYM_FUNC_*`` and ``SYM_CODE_*`` enumerated above.
So in most cases, developers should write something like in the following
example, having some asm instructions in between the macros, of course::
- SYM_FUNC_START(function_hook)
+ SYM_FUNC_START(memset)
... asm insns ...
- SYM_FUNC_END(function_hook)
+ SYM_FUNC_END(memset)
In fact, this kind of annotation corresponds to the now deprecated ``ENTRY``
and ``ENDPROC`` macros.
diff --git a/arch/x86/kernel/ftrace_32.S b/arch/x86/kernel/ftrace_32.S
index 8ed1f5d371f0..e8a9f8370112 100644
--- a/arch/x86/kernel/ftrace_32.S
+++ b/arch/x86/kernel/ftrace_32.S
@@ -12,18 +12,16 @@
#include <asm/frame.h>
#include <asm/asm-offsets.h>
-# define function_hook __fentry__
-EXPORT_SYMBOL(__fentry__)
-
#ifdef CONFIG_FRAME_POINTER
# define MCOUNT_FRAME 1 /* using frame = true */
#else
# define MCOUNT_FRAME 0 /* using frame = false */
#endif
-SYM_FUNC_START(function_hook)
+SYM_FUNC_START(__fentry__)
ret
-SYM_FUNC_END(function_hook)
+SYM_FUNC_END(__fentry__)
+EXPORT_SYMBOL(__fentry__)
SYM_CODE_START(ftrace_caller)
diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index 69c8d1b9119e..6e8961ca3605 100644
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -14,9 +14,6 @@
.code64
.section .entry.text, "ax"
-# define function_hook __fentry__
-EXPORT_SYMBOL(__fentry__)
-
#ifdef CONFIG_FRAME_POINTER
/* Save parent and function stack frames (rip and rbp) */
# define MCOUNT_FRAME_SIZE (8+16*2)
@@ -132,9 +129,10 @@ EXPORT_SYMBOL(__fentry__)
#ifdef CONFIG_DYNAMIC_FTRACE
-SYM_FUNC_START(function_hook)
+SYM_FUNC_START(__fentry__)
retq
-SYM_FUNC_END(function_hook)
+SYM_FUNC_END(__fentry__)
+EXPORT_SYMBOL(__fentry__)
SYM_FUNC_START(ftrace_caller)
/* save_mcount_regs fills in first two parameters */
@@ -248,7 +246,7 @@ SYM_FUNC_END(ftrace_regs_caller)
#else /* ! CONFIG_DYNAMIC_FTRACE */
-SYM_FUNC_START(function_hook)
+SYM_FUNC_START(__fentry__)
cmpq $ftrace_stub, ftrace_trace_function
jnz trace
@@ -279,7 +277,8 @@ trace:
restore_mcount_regs
jmp fgraph_trace
-SYM_FUNC_END(function_hook)
+SYM_FUNC_END(__fentry__)
+EXPORT_SYMBOL(__fentry__)
#endif /* CONFIG_DYNAMIC_FTRACE */
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
--
2.21.0
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
