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Subject[RFC PATCH 3/5] livepatch: ftrace: arm64: Add support for -mfentry on arm64
Date
This patch depends on the compiler's mfentry feature for arm64 that
proposed by this patchset. If the kernel is compiled with this feature,
the entry of each function like:
foo:
mov x9, x30
bl __fentry__
mov x30, x9
When -mfentry is used, the call is to '__fentry__' and not '_mcount'
and is done before the function's stack frame is set up. So __fentry__
is responsibel to protect parameter registers and corruptible registers.

Signed-off-by: Li Bin <huawei.libin@huawei.com>
---
arch/arm64/Kconfig | 1 +
arch/arm64/include/asm/ftrace.h | 5 +++
arch/arm64/kernel/arm64ksyms.c | 4 ++
arch/arm64/kernel/entry-ftrace.S | 59 +++++++++++++++++++++++++++++++++++--
scripts/recordmcount.pl | 2 +-
5 files changed, 66 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index ea435c9..7bb2468 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -60,6 +60,7 @@ config ARM64
select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
select HAVE_EFFICIENT_UNALIGNED_ACCESS
select HAVE_FTRACE_MCOUNT_RECORD
+ select HAVE_FENTRY
select HAVE_FUNCTION_TRACER
select HAVE_FUNCTION_GRAPH_TRACER
select HAVE_GENERIC_DMA_COHERENT
diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
index a7722b9..08eab52 100644
--- a/arch/arm64/include/asm/ftrace.h
+++ b/arch/arm64/include/asm/ftrace.h
@@ -13,7 +13,11 @@

#include <asm/insn.h>

+#ifdef CC_USING_FENTRY
+#define MCOUNT_ADDR ((unsigned long)__fentry__)
+#else
#define MCOUNT_ADDR ((unsigned long)_mcount)
+#endif
#define MCOUNT_INSN_SIZE AARCH64_INSN_SIZE

#ifdef CONFIG_DYNAMIC_FTRACE
@@ -24,6 +28,7 @@
#include <linux/compat.h>

extern void _mcount(unsigned long);
+extern void __fentry__(unsigned long);
extern void *return_address(unsigned int);

struct dyn_arch_ftrace {
diff --git a/arch/arm64/kernel/arm64ksyms.c b/arch/arm64/kernel/arm64ksyms.c
index a85843d..f0455d3 100644
--- a/arch/arm64/kernel/arm64ksyms.c
+++ b/arch/arm64/kernel/arm64ksyms.c
@@ -63,5 +63,9 @@ EXPORT_SYMBOL(change_bit);
EXPORT_SYMBOL(test_and_change_bit);

#ifdef CONFIG_FUNCTION_TRACER
+#ifdef CC_USING_FENTRY
+EXPORT_SYMBOL(__fentry__);
+#else
EXPORT_SYMBOL(_mcount);
#endif
+#endif
diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S
index fde793b..18cfe5b 100644
--- a/arch/arm64/kernel/entry-ftrace.S
+++ b/arch/arm64/kernel/entry-ftrace.S
@@ -93,27 +93,57 @@
ldr \reg, [\reg]
.endm

+ /* for instrumented function's parent */
+ .macro fentry_get_parent_fp reg
+ ldr \reg, [x29]
+ .endm
+
/* for instrumented function */
.macro mcount_get_pc0 reg
mcount_adjust_addr \reg, x30
.endm

+ /* for instrumented function */
+ .macro fentry_get_pc0 reg
+ mcount_adjust_addr \reg, x30
+ .endm
+
.macro mcount_get_pc reg
ldr \reg, [x29, #8]
mcount_adjust_addr \reg, \reg
.endm

+ .macro fentry_get_pc reg
+ ldr \reg, [x29, #8]
+ mcount_adjust_addr \reg, \reg
+ .endm
+
.macro mcount_get_lr reg
ldr \reg, [x29]
ldr \reg, [\reg, #8]
mcount_adjust_addr \reg, \reg
.endm

+ .macro fentry_get_lr reg, base
+ ldr \reg, [\base, #72] //S_X9
+ mcount_adjust_addr \reg, \reg
+ .endm
+
.macro mcount_get_lr_addr reg
ldr \reg, [x29]
add \reg, \reg, #8
.endm

+ .macro fentry_get_lr_addr reg, base
+ add \reg, \base, #72 //S_X9
+ .endm
+
+#ifdef CC_USING_FENTRY
+#define function_hook __fentry__
+#else
+#define function_hook _mcount
+#endif
+
#ifndef CONFIG_DYNAMIC_FTRACE
/*
* void _mcount(unsigned long return_address)
@@ -123,7 +153,7 @@
* - tracer function to probe instrumented function's entry,
* - ftrace_graph_caller to set up an exit hook
*/
-ENTRY(_mcount)
+ENTRY(function_hook)
mcount_enter
save_mcount_regs

@@ -133,8 +163,13 @@ ENTRY(_mcount)
cmp x0, x2 // if (ftrace_trace_function
b.eq skip_ftrace_call // != ftrace_stub) {

+#ifdef CC_USING_FENTRY
+ fentry_get_pc x0 // function's pc
+ fentry_get_lr x1, sp // function's lr (= parent's pc)
+#else
mcount_get_pc x0 // function's pc
mcount_get_lr x1 // function's lr (= parent's pc)
+#endif
blr x2 // (*ftrace_trace_function)(pc, lr);

#ifndef CONFIG_FUNCTION_GRAPH_TRACER
@@ -161,7 +196,7 @@ skip_ftrace_call:
restore_mcount_regs
mcount_exit
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
-ENDPROC(_mcount)
+ENDPROC(function_hook)

#else /* CONFIG_DYNAMIC_FTRACE */
/*
@@ -170,9 +205,9 @@ ENDPROC(_mcount)
* and later on, NOP to branch to ftrace_caller() when enabled or branch to
* NOP when disabled per-function base.
*/
-ENTRY(_mcount)
+ENTRY(function_hook)
ret
-ENDPROC(_mcount)
+ENDPROC(function_hook)

/*
* void ftrace_caller(unsigned long return_address)
@@ -189,8 +224,13 @@ ENTRY(ftrace_caller)

adrp x0, function_trace_op
ldr x2, [x0, #:lo12:function_trace_op]
+#ifdef CC_USING_FENTRY
+ fentry_get_pc0 x0 // function's pc
+ fentry_get_lr x1, sp // function's lr
+#else
mcount_get_pc0 x0 // function's pc
mcount_get_lr x1 // function's lr
+#endif
mov x3, #0

.global ftrace_call
@@ -237,8 +277,13 @@ ENTRY(ftrace_regs_caller)

adrp x0, function_trace_op
ldr x2, [x0, #:lo12:function_trace_op]
+#ifdef CC_USING_FENTRY
+ fentry_get_pc0 x0 // function's pc
+ fentry_get_lr x1, sp // function's lr
+#else
mcount_get_pc0 x0 // function's pc
mcount_get_lr x1 // function's lr
+#endif
mov x3, sp

.global ftrace_regs_call
@@ -282,9 +327,15 @@ ENDPROC(ftrace_stub)
* and run return_to_handler() later on its exit.
*/
ENTRY(ftrace_graph_caller)
+#ifdef CC_USING_FENTRY
+ fentry_get_lr_addr x0, sp // pointer to function's saved lr
+ fentry_get_pc x1 // function's pc
+ fentry_get_parent_fp x2 // parent's fp
+#else
mcount_get_lr_addr x0 // pointer to function's saved lr
mcount_get_pc x1 // function's pc
mcount_get_parent_fp x2 // parent's fp
+#endif
bl prepare_ftrace_return // prepare_ftrace_return(&lr, pc, fp)

restore_mcount_regs
diff --git a/scripts/recordmcount.pl b/scripts/recordmcount.pl
index 826470d..5020d96 100755
--- a/scripts/recordmcount.pl
+++ b/scripts/recordmcount.pl
@@ -279,7 +279,7 @@ if ($arch eq "x86_64") {
} elsif ($arch eq "arm64") {
$alignment = 3;
$section_type = '%progbits';
- $mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_AARCH64_CALL26\\s+_mcount\$";
+ $mcount_regex = "^\\s*([0-9a-fA-F]+):\\s*R_AARCH64_CALL26\\s+(_mcount|__fentry__)\$";
$type = ".quad";
} elsif ($arch eq "ia64") {
$mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$";
--
1.7.1


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