linux-kernel - [PATCH 2/5] s390/ftrace: optimize patched mcount calling code

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Message-ID: <20140815115936.GC4215@osiris>
Date:	Fri, 15 Aug 2014 13:59:36 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Vojtech Pavlik <vojtech@...e.cz>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Jiri Kosina <jkosina@...e.cz>, Jiri Slaby <jslaby@...e.cz>,
	linux390@...ibm.com, linux-s390@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/5] s390/ftrace: optimize patched mcount calling code

We can skip executing the first "stg" instruction of the patched
and disabled mcount code in function tracer enabled kernels.
This saves one instruction per function.

Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
---
 arch/s390/include/asm/ftrace.h |  2 +-
 arch/s390/kernel/ftrace.c      | 16 ++++++++--------
 scripts/recordmcount.c         |  2 +-
 scripts/recordmcount.pl        |  2 +-
 4 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/arch/s390/include/asm/ftrace.h b/arch/s390/include/asm/ftrace.h
index bf246dae1367..4b264caa0704 100644
--- a/arch/s390/include/asm/ftrace.h
+++ b/arch/s390/include/asm/ftrace.h
@@ -18,7 +18,7 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
 #endif /* __ASSEMBLY__ */
 
 #ifdef CONFIG_64BIT
-#define MCOUNT_INSN_SIZE  12
+#define MCOUNT_INSN_SIZE  18
 #else
 #define MCOUNT_INSN_SIZE  22
 #endif
diff --git a/arch/s390/kernel/ftrace.c b/arch/s390/kernel/ftrace.c
index 54d6493c4a56..ae4141fbcb07 100644
--- a/arch/s390/kernel/ftrace.c
+++ b/arch/s390/kernel/ftrace.c
@@ -25,22 +25,22 @@ void ftrace_enable_insn(void);
 #ifdef CONFIG_64BIT
 /*
  * The 64-bit mcount code looks like this:
- *	stg	%r14,8(%r15)		# offset 0
+ * >	stg	%r14,8(%r15)		# offset 0
  * >	larl	%r1,<&counter>		# offset 6
  * >	brasl	%r14,_mcount		# offset 12
  *	lg	%r14,8(%r15)		# offset 18
- * Total length is 24 bytes. The middle two instructions of the mcount
+ * Total length is 24 bytes. The first three instructions of the mcount
  * block get overwritten by ftrace_make_nop / ftrace_make_call.
  * The 64-bit enabled ftrace code block looks like this:
- *	stg	%r14,8(%r15)		# offset 0
+ * >	stg	%r14,8(%r15)		# offset 0
  * >	lg	%r1,__LC_FTRACE_FUNC	# offset 6
  * >	lgr	%r0,%r0			# offset 12
  * >	basr	%r14,%r1		# offset 16
  *	lg	%r14,8(%15)		# offset 18
  * The return points of the mcount/ftrace function have the same offset 18.
  * The 64-bit disable ftrace code block looks like this:
- *	stg	%r14,8(%r15)		# offset 0
- * >	jg	.+18			# offset 6
+ * >	jg	.+24			# offset 6
+ * >	lg	%r1,__LC_FTRACE_FUNC	# offset 6
  * >	lgr	%r0,%r0			# offset 12
  * >	basr	%r14,%r1		# offset 16
  *	lg	%r14,8(%15)		# offset 18
@@ -50,13 +50,13 @@ void ftrace_enable_insn(void);
 asm(
 	"	.align	4\n"
 	"ftrace_disable_code:\n"
-	"	jg	0f\n"
+	"	jg	.+24\n"
+	"	lg	%r1,"__stringify(__LC_FTRACE_FUNC)"\n"
 	"	lgr	%r0,%r0\n"
 	"	basr	%r14,%r1\n"
-	"0:\n"
 	"	.align	4\n"
 	"ftrace_enable_insn:\n"
-	"	lg	%r1,"__stringify(__LC_FTRACE_FUNC)"\n");
+	"	stg	%r14,8(%r15)\n");
 
 #define FTRACE_INSN_SIZE	6
 
diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
index 650ecc83d7d7..efca581d8553 100644
--- a/scripts/recordmcount.c
+++ b/scripts/recordmcount.c
@@ -408,7 +408,7 @@ do_file(char const *const fname)
 		}
 		if (w2(ghdr->e_machine) == EM_S390) {
 			reltype = R_390_64;
-			mcount_adjust_64 = -8;
+			mcount_adjust_64 = -14;
 		}
 		if (w2(ghdr->e_machine) == EM_MIPS) {
 			reltype = R_MIPS_64;
diff --git a/scripts/recordmcount.pl b/scripts/recordmcount.pl
index 397b6b84e8c5..2e260fc27a60 100755
--- a/scripts/recordmcount.pl
+++ b/scripts/recordmcount.pl
@@ -250,7 +250,7 @@ if ($arch eq "x86_64") {
 
 } elsif ($arch eq "s390" && $bits == 64) {
     $mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_390_(PC|PLT)32DBL\\s+_mcount\\+0x2\$";
-    $mcount_adjust = -8;
+    $mcount_adjust = -14;
     $alignment = 8;
     $type = ".quad";
     $ld .= " -m elf64_s390";
-- 
1.8.5.5

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