[PATCH 2/2] ftrace: re-enable dynamic ftrace for ARM
Rabin Vincent
rabin at rab.in
Sun Jan 31 12:33:16 EST 2010
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 at goodmis.org>
Cc: Frederic Weisbecker <fweisbec at gmail.com>
Cc: Ingo Molnar <mingo at redhat.com>
Cc: Abhishek Sagar <sagar.abhishek at gmail.com>
Cc: Uwe Kleine-König <u.kleine-koenig at pengutronix.de>
Signed-off-by: Rabin Vincent <rabin at rab.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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