[PATCH -next V7 3/7] riscv: ftrace: Reduce the detour code size to half
guoren at kernel.org
guoren at kernel.org
Thu Jan 12 01:05:59 PST 2023
From: Guo Ren <guoren at linux.alibaba.com>
Use a temporary register to reduce the size of detour code from 16 bytes to
8 bytes. The previous implementation is from 'commit afc76b8b8011 ("riscv:
Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT")'.
Before the patch:
<func_prolog>:
0: REG_S ra, -SZREG(sp)
4: auipc ra, ?
8: jalr ?(ra)
12: REG_L ra, -SZREG(sp)
(func_boddy)
After the patch:
<func_prolog>:
0: auipc t0, ?
4: jalr t0, ?(t0)
(func_boddy)
This patch not just reduces the size of detour code, but also fixes an
important issue:
An Ftrace callback registered with FTRACE_OPS_FL_IPMODIFY flag can
actually change the instruction pointer, e.g. to "replace" the given
kernel function with a new one, which is needed for livepatching, etc.
In this case, the trampoline (ftrace_regs_caller) would not return to
<func_prolog+12> but would rather jump to the new function. So, "REG_L
ra, -SZREG(sp)" would not run and the original return address would not
be restored. The kernel is likely to hang or crash as a result.
This can be easily demonstrated if one tries to "replace", say,
cmdline_proc_show() with a new function with the same signature using
instruction_pointer_set(&fregs->regs, new_func_addr) in the Ftrace
callback.
Link: https://lore.kernel.org/linux-riscv/20221122075440.1165172-1-suagrfillet@gmail.com/
Link: https://lore.kernel.org/linux-riscv/d7d5730b-ebef-68e5-5046-e763e1ee6164@yadro.com/
Co-developed-by: Song Shuai <suagrfillet at gmail.com>
Signed-off-by: Song Shuai <suagrfillet at gmail.com>
Signed-off-by: Guo Ren <guoren at linux.alibaba.com>
Signed-off-by: Guo Ren <guoren at kernel.org>
Cc: Evgenii Shatokhin <e.shatokhin at yadro.com>
---
arch/riscv/Makefile | 4 +-
arch/riscv/include/asm/ftrace.h | 50 +++++++++++++++++++------
arch/riscv/kernel/ftrace.c | 65 ++++++++++-----------------------
arch/riscv/kernel/mcount-dyn.S | 42 ++++++++-------------
4 files changed, 75 insertions(+), 86 deletions(-)
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index ea5a91da6897..3c9aaf67ed79 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -12,9 +12,9 @@ ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
LDFLAGS_vmlinux := --no-relax
KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
ifeq ($(CONFIG_RISCV_ISA_C),y)
- CC_FLAGS_FTRACE := -fpatchable-function-entry=8
-else
CC_FLAGS_FTRACE := -fpatchable-function-entry=4
+else
+ CC_FLAGS_FTRACE := -fpatchable-function-entry=2
endif
endif
diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
index 04dad3380041..9e73922e1e2e 100644
--- a/arch/riscv/include/asm/ftrace.h
+++ b/arch/riscv/include/asm/ftrace.h
@@ -42,6 +42,14 @@ struct dyn_arch_ftrace {
* 2) jalr: setting low-12 offset to ra, jump to ra, and set ra to
* return address (original pc + 4)
*
+ *<ftrace enable>:
+ * 0: auipc t0/ra, 0x?
+ * 4: jalr t0/ra, ?(t0/ra)
+ *
+ *<ftrace disable>:
+ * 0: nop
+ * 4: nop
+ *
* Dynamic ftrace generates probes to call sites, so we must deal with
* both auipc and jalr at the same time.
*/
@@ -52,25 +60,43 @@ struct dyn_arch_ftrace {
#define AUIPC_OFFSET_MASK (0xfffff000)
#define AUIPC_PAD (0x00001000)
#define JALR_SHIFT 20
-#define JALR_BASIC (0x000080e7)
-#define AUIPC_BASIC (0x00000097)
+#define JALR_RA (0x000080e7)
+#define AUIPC_RA (0x00000097)
+#define JALR_T0 (0x000282e7)
+#define AUIPC_T0 (0x00000297)
#define NOP4 (0x00000013)
-#define make_call(caller, callee, call) \
+#define to_jalr_t0(offset) \
+ (((offset & JALR_OFFSET_MASK) << JALR_SHIFT) | JALR_T0)
+
+#define to_auipc_t0(offset) \
+ ((offset & JALR_SIGN_MASK) ? \
+ (((offset & AUIPC_OFFSET_MASK) + AUIPC_PAD) | AUIPC_T0) : \
+ ((offset & AUIPC_OFFSET_MASK) | AUIPC_T0))
+
+#define make_call_t0(caller, callee, call) \
do { \
- call[0] = to_auipc_insn((unsigned int)((unsigned long)callee - \
- (unsigned long)caller)); \
- call[1] = to_jalr_insn((unsigned int)((unsigned long)callee - \
- (unsigned long)caller)); \
+ unsigned int offset = \
+ (unsigned long) callee - (unsigned long) caller; \
+ call[0] = to_auipc_t0(offset); \
+ call[1] = to_jalr_t0(offset); \
} while (0)
-#define to_jalr_insn(offset) \
- (((offset & JALR_OFFSET_MASK) << JALR_SHIFT) | JALR_BASIC)
+#define to_jalr_ra(offset) \
+ (((offset & JALR_OFFSET_MASK) << JALR_SHIFT) | JALR_RA)
-#define to_auipc_insn(offset) \
+#define to_auipc_ra(offset) \
((offset & JALR_SIGN_MASK) ? \
- (((offset & AUIPC_OFFSET_MASK) + AUIPC_PAD) | AUIPC_BASIC) : \
- ((offset & AUIPC_OFFSET_MASK) | AUIPC_BASIC))
+ (((offset & AUIPC_OFFSET_MASK) + AUIPC_PAD) | AUIPC_RA) : \
+ ((offset & AUIPC_OFFSET_MASK) | AUIPC_RA))
+
+#define make_call_ra(caller, callee, call) \
+do { \
+ unsigned int offset = \
+ (unsigned long) callee - (unsigned long) caller; \
+ call[0] = to_auipc_ra(offset); \
+ call[1] = to_jalr_ra(offset); \
+} while (0)
/*
* Let auipc+jalr be the basic *mcount unit*, so we make it 8 bytes here.
diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
index 2086f6585773..5bff37af4770 100644
--- a/arch/riscv/kernel/ftrace.c
+++ b/arch/riscv/kernel/ftrace.c
@@ -55,12 +55,15 @@ static int ftrace_check_current_call(unsigned long hook_pos,
}
static int __ftrace_modify_call(unsigned long hook_pos, unsigned long target,
- bool enable)
+ bool enable, bool ra)
{
unsigned int call[2];
unsigned int nops[2] = {NOP4, NOP4};
- make_call(hook_pos, target, call);
+ if (ra)
+ make_call_ra(hook_pos, target, call);
+ else
+ make_call_t0(hook_pos, target, call);
/* Replace the auipc-jalr pair at once. Return -EPERM on write error. */
if (patch_text_nosync
@@ -70,42 +73,13 @@ static int __ftrace_modify_call(unsigned long hook_pos, unsigned long target,
return 0;
}
-/*
- * Put 5 instructions with 16 bytes at the front of function within
- * patchable function entry nops' area.
- *
- * 0: REG_S ra, -SZREG(sp)
- * 1: auipc ra, 0x?
- * 2: jalr -?(ra)
- * 3: REG_L ra, -SZREG(sp)
- *
- * So the opcodes is:
- * 0: 0xfe113c23 (sd)/0xfe112e23 (sw)
- * 1: 0x???????? -> auipc
- * 2: 0x???????? -> jalr
- * 3: 0xff813083 (ld)/0xffc12083 (lw)
- */
-#if __riscv_xlen == 64
-#define INSN0 0xfe113c23
-#define INSN3 0xff813083
-#elif __riscv_xlen == 32
-#define INSN0 0xfe112e23
-#define INSN3 0xffc12083
-#endif
-
-#define FUNC_ENTRY_SIZE 16
-#define FUNC_ENTRY_JMP 4
-
int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
- unsigned int call[4] = {INSN0, 0, 0, INSN3};
- unsigned long target = addr;
- unsigned long caller = rec->ip + FUNC_ENTRY_JMP;
+ unsigned int call[2];
- call[1] = to_auipc_insn((unsigned int)(target - caller));
- call[2] = to_jalr_insn((unsigned int)(target - caller));
+ make_call_t0(rec->ip, addr, call);
- if (patch_text_nosync((void *)rec->ip, call, FUNC_ENTRY_SIZE))
+ if (patch_text_nosync((void *)rec->ip, call, MCOUNT_INSN_SIZE))
return -EPERM;
return 0;
@@ -114,15 +88,14 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
unsigned long addr)
{
- unsigned int nops[4] = {NOP4, NOP4, NOP4, NOP4};
+ unsigned int nops[2] = {NOP4, NOP4};
- if (patch_text_nosync((void *)rec->ip, nops, FUNC_ENTRY_SIZE))
+ if (patch_text_nosync((void *)rec->ip, nops, MCOUNT_INSN_SIZE))
return -EPERM;
return 0;
}
-
/*
* This is called early on, and isn't wrapped by
* ftrace_arch_code_modify_{prepare,post_process}() and therefor doesn't hold
@@ -144,10 +117,10 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
int ftrace_update_ftrace_func(ftrace_func_t func)
{
int ret = __ftrace_modify_call((unsigned long)&ftrace_call,
- (unsigned long)func, true);
+ (unsigned long)func, true, true);
if (!ret) {
ret = __ftrace_modify_call((unsigned long)&ftrace_regs_call,
- (unsigned long)func, true);
+ (unsigned long)func, true, true);
}
return ret;
@@ -159,16 +132,16 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
unsigned long addr)
{
unsigned int call[2];
- unsigned long caller = rec->ip + FUNC_ENTRY_JMP;
+ unsigned long caller = rec->ip;
int ret;
- make_call(caller, old_addr, call);
+ make_call_t0(caller, old_addr, call);
ret = ftrace_check_current_call(caller, call);
if (ret)
return ret;
- return __ftrace_modify_call(caller, addr, true);
+ return __ftrace_modify_call(caller, addr, true, false);
}
#endif
@@ -203,12 +176,12 @@ int ftrace_enable_ftrace_graph_caller(void)
int ret;
ret = __ftrace_modify_call((unsigned long)&ftrace_graph_call,
- (unsigned long)&prepare_ftrace_return, true);
+ (unsigned long)&prepare_ftrace_return, true, true);
if (ret)
return ret;
return __ftrace_modify_call((unsigned long)&ftrace_graph_regs_call,
- (unsigned long)&prepare_ftrace_return, true);
+ (unsigned long)&prepare_ftrace_return, true, true);
}
int ftrace_disable_ftrace_graph_caller(void)
@@ -216,12 +189,12 @@ int ftrace_disable_ftrace_graph_caller(void)
int ret;
ret = __ftrace_modify_call((unsigned long)&ftrace_graph_call,
- (unsigned long)&prepare_ftrace_return, false);
+ (unsigned long)&prepare_ftrace_return, false, true);
if (ret)
return ret;
return __ftrace_modify_call((unsigned long)&ftrace_graph_regs_call,
- (unsigned long)&prepare_ftrace_return, false);
+ (unsigned long)&prepare_ftrace_return, false, true);
}
#endif /* CONFIG_DYNAMIC_FTRACE */
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S
index d171eca623b6..125de818d1ba 100644
--- a/arch/riscv/kernel/mcount-dyn.S
+++ b/arch/riscv/kernel/mcount-dyn.S
@@ -13,8 +13,8 @@
.text
-#define FENTRY_RA_OFFSET 12
-#define ABI_SIZE_ON_STACK 72
+#define FENTRY_RA_OFFSET 8
+#define ABI_SIZE_ON_STACK 80
#define ABI_A0 0
#define ABI_A1 8
#define ABI_A2 16
@@ -23,10 +23,10 @@
#define ABI_A5 40
#define ABI_A6 48
#define ABI_A7 56
-#define ABI_RA 64
+#define ABI_T0 64
+#define ABI_RA 72
.macro SAVE_ABI
- addi sp, sp, -SZREG
addi sp, sp, -ABI_SIZE_ON_STACK
REG_S a0, ABI_A0(sp)
@@ -37,6 +37,7 @@
REG_S a5, ABI_A5(sp)
REG_S a6, ABI_A6(sp)
REG_S a7, ABI_A7(sp)
+ REG_S t0, ABI_T0(sp)
REG_S ra, ABI_RA(sp)
.endm
@@ -49,24 +50,18 @@
REG_L a5, ABI_A5(sp)
REG_L a6, ABI_A6(sp)
REG_L a7, ABI_A7(sp)
+ REG_L t0, ABI_T0(sp)
REG_L ra, ABI_RA(sp)
addi sp, sp, ABI_SIZE_ON_STACK
- addi sp, sp, SZREG
.endm
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
.macro SAVE_ALL
- addi sp, sp, -SZREG
addi sp, sp, -PT_SIZE_ON_STACK
- REG_S x1, PT_EPC(sp)
- addi sp, sp, PT_SIZE_ON_STACK
- REG_L x1, (sp)
- addi sp, sp, -PT_SIZE_ON_STACK
+ REG_S t0, PT_EPC(sp)
REG_S x1, PT_RA(sp)
- REG_L x1, PT_EPC(sp)
-
REG_S x2, PT_SP(sp)
REG_S x3, PT_GP(sp)
REG_S x4, PT_TP(sp)
@@ -100,15 +95,11 @@
.endm
.macro RESTORE_ALL
+ REG_L t0, PT_EPC(sp)
REG_L x1, PT_RA(sp)
- addi sp, sp, PT_SIZE_ON_STACK
- REG_S x1, (sp)
- addi sp, sp, -PT_SIZE_ON_STACK
- REG_L x1, PT_EPC(sp)
REG_L x2, PT_SP(sp)
REG_L x3, PT_GP(sp)
REG_L x4, PT_TP(sp)
- REG_L x5, PT_T0(sp)
REG_L x6, PT_T1(sp)
REG_L x7, PT_T2(sp)
REG_L x8, PT_S0(sp)
@@ -137,17 +128,16 @@
REG_L x31, PT_T6(sp)
addi sp, sp, PT_SIZE_ON_STACK
- addi sp, sp, SZREG
.endm
#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
ENTRY(ftrace_caller)
SAVE_ABI
- addi a0, ra, -FENTRY_RA_OFFSET
+ addi a0, t0, -FENTRY_RA_OFFSET
la a1, function_trace_op
REG_L a2, 0(a1)
- REG_L a1, ABI_SIZE_ON_STACK(sp)
+ mv a1, ra
mv a3, sp
ftrace_call:
@@ -155,8 +145,8 @@ ftrace_call:
call ftrace_stub
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
- addi a0, sp, ABI_SIZE_ON_STACK
- REG_L a1, ABI_RA(sp)
+ addi a0, sp, ABI_RA
+ REG_L a1, ABI_T0(sp)
addi a1, a1, -FENTRY_RA_OFFSET
#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
mv a2, s0
@@ -166,17 +156,17 @@ ftrace_graph_call:
call ftrace_stub
#endif
RESTORE_ABI
- ret
+ jr t0
ENDPROC(ftrace_caller)
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
ENTRY(ftrace_regs_caller)
SAVE_ALL
- addi a0, ra, -FENTRY_RA_OFFSET
+ addi a0, t0, -FENTRY_RA_OFFSET
la a1, function_trace_op
REG_L a2, 0(a1)
- REG_L a1, PT_SIZE_ON_STACK(sp)
+ mv a1, ra
mv a3, sp
ftrace_regs_call:
@@ -196,6 +186,6 @@ ftrace_graph_regs_call:
#endif
RESTORE_ALL
- ret
+ jr t0
ENDPROC(ftrace_regs_caller)
#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
--
2.36.1
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