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Date: Sun, 31 Jan 2010 23:03:16 +0530
From: Rabin Vincent <rabin@....in>
To: linux-kernel@...r.kernel.org
Cc: linux-arm-kernel@...ts.infradead.org, Rabin Vincent <rabin@....in>,
Steven Rostedt <rostedt@...dmis.org>,
Frederic Weisbecker <fweisbec@...il.com>,
Ingo Molnar <mingo@...hat.com>,
Abhishek Sagar <sagar.abhishek@...il.com>,
Uwe Kleine-König
<u.kleine-koenig@...gutronix.de>
Subject: [PATCH 2/2] ftrace: re-enable dynamic ftrace for ARM
This adds mcount recording and updates dynamic ftrace for ARM to work
with the new ftrace dyamic tracing implementation.
With dynamic tracing, mcount() is implemented as a nop. Callsites are
patched on startup with nops, and dynamically patched to call to the
ftrace_caller() routine as needed.
One oddity of the ARM implementation is that we need to handle two kinds
of mcounts. Newer GCC versions renamed the mcount routine (to
__gnu_mcount_nc) and changed the semantics (lr is pushed on the stack
before the call). We detect which one is used at run-time.
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Abhishek Sagar <sagar.abhishek@...il.com>
Cc: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Signed-off-by: Rabin Vincent <rabin@....in>
---
arch/arm/Kconfig | 2 +
arch/arm/include/asm/ftrace.h | 14 +++++
arch/arm/kernel/entry-common.S | 25 ++++++---
arch/arm/kernel/ftrace.c | 122 ++++++++++++++++++++++++++--------------
scripts/recordmcount.pl | 2 +
5 files changed, 115 insertions(+), 50 deletions(-)
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 4c33ca8..dc92691 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -17,6 +17,8 @@ config ARM
select HAVE_KPROBES if (!XIP_KERNEL)
select HAVE_KRETPROBES if (HAVE_KPROBES)
select HAVE_FUNCTION_TRACER if (!XIP_KERNEL)
+ select HAVE_FTRACE_MCOUNT_RECORD if (!XIP_KERNEL)
+ select HAVE_DYNAMIC_FTRACE if (!XIP_KERNEL && !THUMB2_KERNEL)
select HAVE_GENERIC_DMA_COHERENT
select HAVE_KERNEL_GZIP
select HAVE_KERNEL_LZO
diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
index 103f7ee..12f445d 100644
--- a/arch/arm/include/asm/ftrace.h
+++ b/arch/arm/include/asm/ftrace.h
@@ -8,6 +8,20 @@
#ifndef __ASSEMBLY__
extern void mcount(void);
extern void __gnu_mcount_nc(void);
+
+#ifdef CONFIG_DYNAMIC_FTRACE
+struct dyn_arch_ftrace {
+ bool gnu_mcount;
+};
+
+static inline unsigned long ftrace_call_adjust(unsigned long addr)
+{
+ return addr;
+}
+
+extern void ftrace_caller_gnu(void);
+#endif
+
#endif
#endif
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 2c1db77..2a7ab14 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -93,16 +93,25 @@ ENDPROC(ret_from_fork)
#ifdef CONFIG_FUNCTION_TRACER
#ifdef CONFIG_DYNAMIC_FTRACE
+ENTRY(__gnu_mcount_nc)
+ mov ip, lr
+ ldm sp!, {lr}
+ mov pc, ip
+
ENTRY(mcount)
- stmdb sp!, {r0-r3, lr}
- mov r0, lr
- sub r0, r0, #MCOUNT_INSN_SIZE
+ stmdb sp!, {lr}
+ ldr lr, [fp, #-4]
+ ldmia sp!, {pc}
- .globl mcount_call
-mcount_call:
- bl ftrace_stub
- ldr lr, [fp, #-4] @ restore lr
- ldmia sp!, {r0-r3, pc}
+ENTRY(ftrace_caller_gnu)
+ add sp, sp, #4
+
+ /*
+ * We take advantage of the fact that we build with frame pointers and
+ * -mapcs-frame to combine the ftrace_caller implementations for the
+ * two mcounts with just the above adjustment. This will need to be
+ * revisited if Thumb-2 support is added.
+ */
ENTRY(ftrace_caller)
stmdb sp!, {r0-r3, lr}
diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
index c638427..1d5d268 100644
--- a/arch/arm/kernel/ftrace.c
+++ b/arch/arm/kernel/ftrace.c
@@ -7,11 +7,12 @@
*
* Defines low-level handling of mcount calls when the kernel
* is compiled with the -pg flag. When using dynamic ftrace, the
- * mcount call-sites get patched lazily with NOP till they are
- * enabled. All code mutation routines here take effect atomically.
+ * mcount call-sites get patched with NOP till they are enabled.
+ * All code mutation routines here take effect atomically.
*/
#include <linux/ftrace.h>
+#include <linux/uaccess.h>
#include <asm/cacheflush.h>
#include <asm/ftrace.h>
@@ -20,17 +21,26 @@
#define BL_OPCODE 0xeb000000
#define BL_OFFSET_MASK 0x00ffffff
-static unsigned long bl_insn;
-static const unsigned long NOP = 0xe1a00000; /* mov r0, r0 */
+#define NOP 0xe1a00000 /* mov r0, r0 */
+#define GNU_NOP 0xe8bd4000 /* pop {lr} */
-unsigned char *ftrace_nop_replace(void)
+#define GNU_MCOUNT_ADDR ((unsigned long) __gnu_mcount_nc)
+#define GNU_FTRACE_ADDR ((unsigned long) ftrace_caller_gnu)
+
+static unsigned long ftrace_nop_replace(struct dyn_ftrace *rec)
+{
+ return rec->arch.gnu_mcount ? GNU_NOP : NOP;
+}
+
+static unsigned long ftrace_caller_addr(struct dyn_ftrace *rec)
{
- return (char *)&NOP;
+ return rec->arch.gnu_mcount ? GNU_FTRACE_ADDR : FTRACE_ADDR;
}
/* construct a branch (BL) instruction to addr */
-unsigned char *ftrace_call_replace(unsigned long pc, unsigned long addr)
+static unsigned long ftrace_call_replace(unsigned long pc, unsigned long addr)
{
+ unsigned long bl_insn;
long offset;
offset = (long)addr - (long)(pc + PC_OFFSET);
@@ -39,65 +49,93 @@ unsigned char *ftrace_call_replace(unsigned long pc, unsigned long addr)
* doesn't generate branches outside of kernel text.
*/
WARN_ON_ONCE(1);
- return NULL;
+ return 0;
}
offset = (offset >> 2) & BL_OFFSET_MASK;
bl_insn = BL_OPCODE | offset;
- return (unsigned char *)&bl_insn;
+ return bl_insn;
}
-int ftrace_modify_code(unsigned long pc, unsigned char *old_code,
- unsigned char *new_code)
+static int ftrace_modify_code(unsigned long pc, unsigned long old,
+ unsigned long new)
{
- unsigned long err = 0, replaced = 0, old, new;
+ unsigned long replaced;
- old = *(unsigned long *)old_code;
- new = *(unsigned long *)new_code;
+ if (probe_kernel_read(&replaced, (void *)pc, MCOUNT_INSN_SIZE))
+ return -EFAULT;
- __asm__ __volatile__ (
- "1: ldr %1, [%2] \n"
- " cmp %1, %4 \n"
- "2: streq %3, [%2] \n"
- " cmpne %1, %3 \n"
- " movne %0, #2 \n"
- "3:\n"
+ if (replaced != old)
+ return -EINVAL;
- ".section .fixup, \"ax\"\n"
- "4: mov %0, #1 \n"
- " b 3b \n"
- ".previous\n"
+ if (probe_kernel_write((void *)pc, &new, MCOUNT_INSN_SIZE))
+ return -EPERM;
- ".section __ex_table, \"a\"\n"
- " .long 1b, 4b \n"
- " .long 2b, 4b \n"
- ".previous\n"
+ flush_icache_range(pc, pc + MCOUNT_INSN_SIZE);
- : "=r"(err), "=r"(replaced)
- : "r"(pc), "r"(new), "r"(old), "0"(err), "1"(replaced)
- : "memory");
-
- if (!err && (replaced == old))
- flush_icache_range(pc, pc + MCOUNT_INSN_SIZE);
-
- return err;
+ return 0;
}
int ftrace_update_ftrace_func(ftrace_func_t func)
{
- int ret;
unsigned long pc, old;
- unsigned char *new;
+ unsigned long new;
pc = (unsigned long)&ftrace_call;
memcpy(&old, &ftrace_call, MCOUNT_INSN_SIZE);
new = ftrace_call_replace(pc, (unsigned long)func);
- ret = ftrace_modify_code(pc, (unsigned char *)&old, new);
+
+ return ftrace_modify_code(pc, old, new);
+}
+
+int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
+{
+ unsigned long new, old;
+ unsigned long ip = rec->ip;
+
+ old = ftrace_nop_replace(rec);
+ new = ftrace_call_replace(ip, ftrace_caller_addr(rec));
+
+ return ftrace_modify_code(rec->ip, old, new);
+}
+
+static int ftrace_detect_make_nop(struct module *mod,
+ struct dyn_ftrace *rec, unsigned long addr)
+{
+ unsigned long ip = rec->ip;
+ unsigned long call;
+ int ret;
+
+ call = ftrace_call_replace(ip, GNU_MCOUNT_ADDR);
+ ret = ftrace_modify_code(ip, call, GNU_NOP);
+ if (!ret)
+ rec->arch.gnu_mcount = true;
+ else if (ret == -EINVAL) {
+ call = ftrace_call_replace(ip, addr);
+ ret = ftrace_modify_code(ip, call, NOP);
+ }
+
return ret;
}
-/* run from ftrace_init with irqs disabled */
+int ftrace_make_nop(struct module *mod,
+ struct dyn_ftrace *rec, unsigned long addr)
+{
+ unsigned long ip = rec->ip;
+ unsigned long old;
+ unsigned long new;
+
+ if (addr == MCOUNT_ADDR)
+ return ftrace_detect_make_nop(mod, rec, addr);
+
+ old = ftrace_call_replace(ip, ftrace_caller_addr(rec));
+ new = ftrace_nop_replace(rec);
+
+ return ftrace_modify_code(ip, old, new);
+}
+
int __init ftrace_dyn_arch_init(void *data)
{
- ftrace_mcount_set(data);
+ *(unsigned long *)data = 0;
+
return 0;
}
diff --git a/scripts/recordmcount.pl b/scripts/recordmcount.pl
index ea6f6e3..66c1c4b 100755
--- a/scripts/recordmcount.pl
+++ b/scripts/recordmcount.pl
@@ -267,6 +267,8 @@ if ($arch eq "x86_64") {
} elsif ($arch eq "arm") {
$alignment = 2;
$section_type = '%progbits';
+ $mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_ARM_(CALL|PC24)" .
+ "\\s+(__gnu_mcount_nc|mcount)\$";
} elsif ($arch eq "ia64") {
$mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$";
--
1.6.6
--
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