linux-kernel - [PATCH] x86/ftrace: Get rid of function

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Date:   Mon, 21 Oct 2019 16:10:38 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     tip-bot2 for Jiri Slaby <tip-bot2@...utronix.de>,
        linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
        Jiri Slaby <jslaby@...e.cz>, "H. Peter Anvin" <hpa@...or.com>,
        Ingo Molnar <mingo@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-arch@...r.kernel.org, Masami Hiramatsu <mhiramat@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, x86-ml <x86@...nel.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: [PATCH] x86/ftrace: Get rid of function_hook

From: Borislav Petkov <bp@...e.de>

function_hook is used as a better name than the default __fentry__
which is the profiling counter which gcc adds before every function's
prologue. Thus, it is not called from C and cannot have the same
semantics as a pure C function - it saves/restores regs so that a C
function can be called.

Drop the function_hook symbol and use __fentry__ directly for better
alignment with gcc's documentation.

Switch the marking to SYM_CODE_START/_END which is reserved for
non-standard, special functions.

Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Jiri Slaby <jslaby@...e.cz>
Cc: Jonathan Corbet <corbet@....net>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: linux-doc@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: x86@...nel.org
---
 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..77be7e7e5e59 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_CODE_START(__fentry__)
 	ret
-SYM_FUNC_END(function_hook)
+SYM_CODE_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..3029fe4f8547 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_CODE_START(__fentry__)
 	retq
-SYM_FUNC_END(function_hook)
+SYM_CODE_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_CODE_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_CODE_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