RISC-V: Add dynamic ftrace support for RISC-V platforms
This patch set includes the building blocks of dynamic ftrace features
for RISC-V machines. I'm afraid I'm not very familiar with ftrace, but
the code looks OK to me. It's been used to track down a performance
problem in our SPI driver and appears to work acceptably, but we haven't
given it a whole lot of banging yet so there might still be some bugs
lurking around somewhere.
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 04807c7..61dd827 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -114,6 +114,9 @@
select 64BIT
select HAVE_FUNCTION_TRACER
select HAVE_FUNCTION_GRAPH_TRACER
+ select HAVE_FTRACE_MCOUNT_RECORD
+ select HAVE_DYNAMIC_FTRACE
+ select HAVE_DYNAMIC_FTRACE_WITH_REGS
endchoice
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 6719dd3..899226e 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -11,6 +11,9 @@
LDFLAGS :=
OBJCOPYFLAGS := -O binary
LDFLAGS_vmlinux :=
+ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
+ LDFLAGS_vmlinux := --no-relax
+endif
KBUILD_AFLAGS_MODULE += -fPIC
KBUILD_CFLAGS_MODULE += -fPIC
diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
index 66d4175..c6dcc52 100644
--- a/arch/riscv/include/asm/ftrace.h
+++ b/arch/riscv/include/asm/ftrace.h
@@ -8,3 +8,59 @@
#if defined(CONFIG_FUNCTION_GRAPH_TRACER) && defined(CONFIG_FRAME_POINTER)
#define HAVE_FUNCTION_GRAPH_FP_TEST
#endif
+#define HAVE_FUNCTION_GRAPH_RET_ADDR_PTR
+
+#define ARCH_SUPPORTS_FTRACE_OPS 1
+#ifndef __ASSEMBLY__
+void _mcount(void);
+static inline unsigned long ftrace_call_adjust(unsigned long addr)
+{
+ return addr;
+}
+
+struct dyn_arch_ftrace {
+};
+#endif
+
+#ifdef CONFIG_DYNAMIC_FTRACE
+/*
+ * A general call in RISC-V is a pair of insts:
+ * 1) auipc: setting high-20 pc-related bits to ra register
+ * 2) jalr: setting low-12 offset to ra, jump to ra, and set ra to
+ * return address (original pc + 4)
+ *
+ * Dynamic ftrace generates probes to call sites, so we must deal with
+ * both auipc and jalr at the same time.
+ */
+
+#define MCOUNT_ADDR ((unsigned long)_mcount)
+#define JALR_SIGN_MASK (0x00000800)
+#define JALR_OFFSET_MASK (0x00000fff)
+#define AUIPC_OFFSET_MASK (0xfffff000)
+#define AUIPC_PAD (0x00001000)
+#define JALR_SHIFT 20
+#define JALR_BASIC (0x000080e7)
+#define AUIPC_BASIC (0x00000097)
+#define NOP4 (0x00000013)
+
+#define make_call(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)); \
+} while (0)
+
+#define to_jalr_insn(offset) \
+ (((offset & JALR_OFFSET_MASK) << JALR_SHIFT) | JALR_BASIC)
+
+#define to_auipc_insn(offset) \
+ ((offset & JALR_SIGN_MASK) ? \
+ (((offset & AUIPC_OFFSET_MASK) + AUIPC_PAD) | AUIPC_BASIC) : \
+ ((offset & AUIPC_OFFSET_MASK) | AUIPC_BASIC))
+
+/*
+ * Let auipc+jalr be the basic *mcount unit*, so we make it 8 bytes here.
+ */
+#define MCOUNT_INSN_SIZE 8
+#endif
diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index 196f62f..d7bdf88 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -34,7 +34,8 @@
obj-$(CONFIG_SMP) += smpboot.o
obj-$(CONFIG_SMP) += smp.o
obj-$(CONFIG_MODULES) += module.o
-obj-$(CONFIG_FUNCTION_TRACER) += mcount.o
-obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += ftrace.o
+
+obj-$(CONFIG_FUNCTION_TRACER) += mcount.o ftrace.o
+obj-$(CONFIG_DYNAMIC_FTRACE) += mcount-dyn.o
clean:
diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
index d0de68d..1157b6b 100644
--- a/arch/riscv/kernel/ftrace.c
+++ b/arch/riscv/kernel/ftrace.c
@@ -6,9 +6,126 @@
*/
#include <linux/ftrace.h>
+#include <linux/uaccess.h>
+#include <asm/cacheflush.h>
+#ifdef CONFIG_DYNAMIC_FTRACE
+static int ftrace_check_current_call(unsigned long hook_pos,
+ unsigned int *expected)
+{
+ unsigned int replaced[2];
+ unsigned int nops[2] = {NOP4, NOP4};
+
+ /* we expect nops at the hook position */
+ if (!expected)
+ expected = nops;
+
+ /*
+ * Read the text we want to modify;
+ * return must be -EFAULT on read error
+ */
+ if (probe_kernel_read(replaced, (void *)hook_pos, MCOUNT_INSN_SIZE))
+ return -EFAULT;
+
+ /*
+ * Make sure it is what we expect it to be;
+ * return must be -EINVAL on failed comparison
+ */
+ if (memcmp(expected, replaced, sizeof(replaced))) {
+ pr_err("%p: expected (%08x %08x) but get (%08x %08x)",
+ (void *)hook_pos, expected[0], expected[1], replaced[0],
+ replaced[1]);
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
+static int __ftrace_modify_call(unsigned long hook_pos, unsigned long target,
+ bool enable)
+{
+ unsigned int call[2];
+ unsigned int nops[2] = {NOP4, NOP4};
+ int ret = 0;
+
+ make_call(hook_pos, target, call);
+
+ /* replace the auipc-jalr pair at once */
+ ret = probe_kernel_write((void *)hook_pos, enable ? call : nops,
+ MCOUNT_INSN_SIZE);
+ /* return must be -EPERM on write error */
+ if (ret)
+ return -EPERM;
+
+ smp_mb();
+ flush_icache_range((void *)hook_pos, (void *)hook_pos + MCOUNT_INSN_SIZE);
+
+ return 0;
+}
+
+int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
+{
+ int ret = ftrace_check_current_call(rec->ip, NULL);
+
+ if (ret)
+ return ret;
+
+ return __ftrace_modify_call(rec->ip, addr, true);
+}
+
+int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
+ unsigned long addr)
+{
+ unsigned int call[2];
+ int ret;
+
+ make_call(rec->ip, addr, call);
+ ret = ftrace_check_current_call(rec->ip, call);
+
+ if (ret)
+ return ret;
+
+ return __ftrace_modify_call(rec->ip, addr, false);
+}
+
+int ftrace_update_ftrace_func(ftrace_func_t func)
+{
+ int ret = __ftrace_modify_call((unsigned long)&ftrace_call,
+ (unsigned long)func, true);
+ if (!ret) {
+ ret = __ftrace_modify_call((unsigned long)&ftrace_regs_call,
+ (unsigned long)func, true);
+ }
+
+ return ret;
+}
+
+int __init ftrace_dyn_arch_init(void)
+{
+ return 0;
+}
+#endif
+
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
+ unsigned long addr)
+{
+ unsigned int call[2];
+ int ret;
+
+ make_call(rec->ip, old_addr, call);
+ ret = ftrace_check_current_call(rec->ip, call);
+
+ if (ret)
+ return ret;
+
+ return __ftrace_modify_call(rec->ip, addr, true);
+}
+#endif
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
/*
- * Most of this file is copied from arm64.
+ * Most of this function is copied from arm64.
*/
void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
unsigned long frame_pointer)
@@ -34,8 +151,62 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
return;
err = ftrace_push_return_trace(old, self_addr, &trace.depth,
- frame_pointer, NULL);
+ frame_pointer, parent);
if (err == -EBUSY)
return;
*parent = return_hooker;
}
+
+#ifdef CONFIG_DYNAMIC_FTRACE
+extern void ftrace_graph_call(void);
+int ftrace_enable_ftrace_graph_caller(void)
+{
+ unsigned int call[2];
+ static int init_graph = 1;
+ int ret;
+
+ make_call(&ftrace_graph_call, &ftrace_stub, call);
+
+ /*
+ * When enabling graph tracer for the first time, ftrace_graph_call
+ * should contains a call to ftrace_stub. Once it has been disabled,
+ * the 8-bytes at the position becomes NOPs.
+ */
+ if (init_graph) {
+ ret = ftrace_check_current_call((unsigned long)&ftrace_graph_call,
+ call);
+ init_graph = 0;
+ } else {
+ ret = ftrace_check_current_call((unsigned long)&ftrace_graph_call,
+ NULL);
+ }
+
+ if (ret)
+ return ret;
+
+ return __ftrace_modify_call((unsigned long)&ftrace_graph_call,
+ (unsigned long)&prepare_ftrace_return, true);
+}
+
+int ftrace_disable_ftrace_graph_caller(void)
+{
+ unsigned int call[2];
+ int ret;
+
+ make_call(&ftrace_graph_call, &prepare_ftrace_return, call);
+
+ /*
+ * This is to make sure that ftrace_enable_ftrace_graph_caller
+ * did the right thing.
+ */
+ ret = ftrace_check_current_call((unsigned long)&ftrace_graph_call,
+ call);
+
+ if (ret)
+ return ret;
+
+ return __ftrace_modify_call((unsigned long)&ftrace_graph_call,
+ (unsigned long)&prepare_ftrace_return, false);
+}
+#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
new file mode 100644
index 0000000..35a6ed7
--- /dev/null
+++ b/arch/riscv/kernel/mcount-dyn.S
@@ -0,0 +1,239 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (C) 2017 Andes Technology Corporation */
+
+#include <linux/init.h>
+#include <linux/linkage.h>
+#include <asm/asm.h>
+#include <asm/csr.h>
+#include <asm/unistd.h>
+#include <asm/thread_info.h>
+#include <asm/asm-offsets.h>
+#include <asm-generic/export.h>
+#include <asm/ftrace.h>
+
+ .text
+
+ .macro SAVE_ABI_STATE
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ addi sp, sp, -48
+ sd s0, 32(sp)
+ sd ra, 40(sp)
+ addi s0, sp, 48
+ sd t0, 24(sp)
+ sd t1, 16(sp)
+#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
+ sd t2, 8(sp)
+#endif
+#else
+ addi sp, sp, -16
+ sd s0, 0(sp)
+ sd ra, 8(sp)
+ addi s0, sp, 16
+#endif
+ .endm
+
+ .macro RESTORE_ABI_STATE
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ ld s0, 32(sp)
+ ld ra, 40(sp)
+ addi sp, sp, 48
+#else
+ ld ra, 8(sp)
+ ld s0, 0(sp)
+ addi sp, sp, 16
+#endif
+ .endm
+
+ .macro RESTORE_GRAPH_ARGS
+ ld a0, 24(sp)
+ ld a1, 16(sp)
+#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
+ ld a2, 8(sp)
+#endif
+ .endm
+
+ENTRY(ftrace_graph_caller)
+ addi sp, sp, -16
+ sd s0, 0(sp)
+ sd ra, 8(sp)
+ addi s0, sp, 16
+ftrace_graph_call:
+ .global ftrace_graph_call
+ /*
+ * Calling ftrace_enable/disable_ftrace_graph_caller would overwrite the
+ * call below. Check ftrace_modify_all_code for details.
+ */
+ call ftrace_stub
+ ld ra, 8(sp)
+ ld s0, 0(sp)
+ addi sp, sp, 16
+ ret
+ENDPROC(ftrace_graph_caller)
+
+ENTRY(ftrace_caller)
+ /*
+ * a0: the address in the caller when calling ftrace_caller
+ * a1: the caller's return address
+ * a2: the address of global variable function_trace_op
+ */
+ ld a1, -8(s0)
+ addi a0, ra, -MCOUNT_INSN_SIZE
+ la t5, function_trace_op
+ ld a2, 0(t5)
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ /*
+ * the graph tracer (specifically, prepare_ftrace_return) needs these
+ * arguments but for now the function tracer occupies the regs, so we
+ * save them in temporary regs to recover later.
+ */
+ addi t0, s0, -8
+ mv t1, a0
+#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
+ ld t2, -16(s0)
+#endif
+#endif
+
+ SAVE_ABI_STATE
+ftrace_call:
+ .global ftrace_call
+ /*
+ * For the dynamic ftrace to work, here we should reserve at least
+ * 8 bytes for a functional auipc-jalr pair. The following call
+ * serves this purpose.
+ *
+ * Calling ftrace_update_ftrace_func would overwrite the nops below.
+ * Check ftrace_modify_all_code for details.
+ */
+ call ftrace_stub
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ RESTORE_GRAPH_ARGS
+ call ftrace_graph_caller
+#endif
+
+ RESTORE_ABI_STATE
+ ret
+ENDPROC(ftrace_caller)
+
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+ .macro SAVE_ALL
+ addi sp, sp, -(PT_SIZE_ON_STACK+16)
+ sd s0, (PT_SIZE_ON_STACK)(sp)
+ sd ra, (PT_SIZE_ON_STACK+8)(sp)
+ addi s0, sp, (PT_SIZE_ON_STACK+16)
+
+ sd x1, PT_RA(sp)
+ sd x2, PT_SP(sp)
+ sd x3, PT_GP(sp)
+ sd x4, PT_TP(sp)
+ sd x5, PT_T0(sp)
+ sd x6, PT_T1(sp)
+ sd x7, PT_T2(sp)
+ sd x8, PT_S0(sp)
+ sd x9, PT_S1(sp)
+ sd x10, PT_A0(sp)
+ sd x11, PT_A1(sp)
+ sd x12, PT_A2(sp)
+ sd x13, PT_A3(sp)
+ sd x14, PT_A4(sp)
+ sd x15, PT_A5(sp)
+ sd x16, PT_A6(sp)
+ sd x17, PT_A7(sp)
+ sd x18, PT_S2(sp)
+ sd x19, PT_S3(sp)
+ sd x20, PT_S4(sp)
+ sd x21, PT_S5(sp)
+ sd x22, PT_S6(sp)
+ sd x23, PT_S7(sp)
+ sd x24, PT_S8(sp)
+ sd x25, PT_S9(sp)
+ sd x26, PT_S10(sp)
+ sd x27, PT_S11(sp)
+ sd x28, PT_T3(sp)
+ sd x29, PT_T4(sp)
+ sd x30, PT_T5(sp)
+ sd x31, PT_T6(sp)
+ .endm
+
+ .macro RESTORE_ALL
+ ld x1, PT_RA(sp)
+ ld x2, PT_SP(sp)
+ ld x3, PT_GP(sp)
+ ld x4, PT_TP(sp)
+ ld x5, PT_T0(sp)
+ ld x6, PT_T1(sp)
+ ld x7, PT_T2(sp)
+ ld x8, PT_S0(sp)
+ ld x9, PT_S1(sp)
+ ld x10, PT_A0(sp)
+ ld x11, PT_A1(sp)
+ ld x12, PT_A2(sp)
+ ld x13, PT_A3(sp)
+ ld x14, PT_A4(sp)
+ ld x15, PT_A5(sp)
+ ld x16, PT_A6(sp)
+ ld x17, PT_A7(sp)
+ ld x18, PT_S2(sp)
+ ld x19, PT_S3(sp)
+ ld x20, PT_S4(sp)
+ ld x21, PT_S5(sp)
+ ld x22, PT_S6(sp)
+ ld x23, PT_S7(sp)
+ ld x24, PT_S8(sp)
+ ld x25, PT_S9(sp)
+ ld x26, PT_S10(sp)
+ ld x27, PT_S11(sp)
+ ld x28, PT_T3(sp)
+ ld x29, PT_T4(sp)
+ ld x30, PT_T5(sp)
+ ld x31, PT_T6(sp)
+
+ ld s0, (PT_SIZE_ON_STACK)(sp)
+ ld ra, (PT_SIZE_ON_STACK+8)(sp)
+ addi sp, sp, (PT_SIZE_ON_STACK+16)
+ .endm
+
+ .macro RESTORE_GRAPH_REG_ARGS
+ ld a0, PT_T0(sp)
+ ld a1, PT_T1(sp)
+#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
+ ld a2, PT_T2(sp)
+#endif
+ .endm
+
+/*
+ * Most of the contents are the same as ftrace_caller.
+ */
+ENTRY(ftrace_regs_caller)
+ /*
+ * a3: the address of all registers in the stack
+ */
+ ld a1, -8(s0)
+ addi a0, ra, -MCOUNT_INSN_SIZE
+ la t5, function_trace_op
+ ld a2, 0(t5)
+ addi a3, sp, -(PT_SIZE_ON_STACK+16)
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ addi t0, s0, -8
+ mv t1, a0
+#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
+ ld t2, -16(s0)
+#endif
+#endif
+ SAVE_ALL
+
+ftrace_regs_call:
+ .global ftrace_regs_call
+ call ftrace_stub
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ RESTORE_GRAPH_REG_ARGS
+ call ftrace_graph_caller
+#endif
+
+ RESTORE_ALL
+ ret
+ENDPROC(ftrace_regs_caller)
+#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
diff --git a/arch/riscv/kernel/mcount.S b/arch/riscv/kernel/mcount.S
index c46a778..ce9bdc5 100644
--- a/arch/riscv/kernel/mcount.S
+++ b/arch/riscv/kernel/mcount.S
@@ -32,13 +32,13 @@
addi s0, sp, 32
.endm
- .macro STORE_ABI_STATE
+ .macro RESTORE_ABI_STATE
ld ra, 8(sp)
ld s0, 0(sp)
addi sp, sp, 16
.endm
- .macro STORE_RET_ABI_STATE
+ .macro RESTORE_RET_ABI_STATE
ld ra, 24(sp)
ld s0, 16(sp)
ld a0, 8(sp)
@@ -46,6 +46,10 @@
.endm
ENTRY(ftrace_stub)
+#ifdef CONFIG_DYNAMIC_FTRACE
+ .global _mcount
+ .set _mcount, ftrace_stub
+#endif
ret
ENDPROC(ftrace_stub)
@@ -66,15 +70,15 @@
#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
mv a0, t6
#endif
- la t0, ftrace_return_to_handler
- jalr t0
+ call ftrace_return_to_handler
mv a1, a0
- STORE_RET_ABI_STATE
+ RESTORE_RET_ABI_STATE
jalr a1
ENDPROC(return_to_handler)
EXPORT_SYMBOL(return_to_handler)
#endif
+#ifndef CONFIG_DYNAMIC_FTRACE
ENTRY(_mcount)
la t4, ftrace_stub
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
@@ -104,9 +108,8 @@
ld a2, -16(s0)
#endif
SAVE_ABI_STATE
- la t0, prepare_ftrace_return
- jalr t0
- STORE_ABI_STATE
+ call prepare_ftrace_return
+ RESTORE_ABI_STATE
ret
#endif
@@ -120,7 +123,8 @@
SAVE_ABI_STATE
jalr t5
- STORE_ABI_STATE
+ RESTORE_ABI_STATE
ret
ENDPROC(_mcount)
EXPORT_SYMBOL(_mcount)
+#endif
diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
index 559aae7..a4b1d943 100644
--- a/arch/riscv/kernel/stacktrace.c
+++ b/arch/riscv/kernel/stacktrace.c
@@ -18,6 +18,7 @@
#include <linux/sched/debug.h>
#include <linux/sched/task_stack.h>
#include <linux/stacktrace.h>
+#include <linux/ftrace.h>
#ifdef CONFIG_FRAME_POINTER
@@ -63,7 +64,12 @@ static void notrace walk_stackframe(struct task_struct *task,
frame = (struct stackframe *)fp - 1;
sp = fp;
fp = frame->fp;
+#ifdef HAVE_FUNCTION_GRAPH_RET_ADDR_PTR
+ pc = ftrace_graph_ret_addr(current, NULL, frame->ra,
+ (unsigned long *)(fp - 8));
+#else
pc = frame->ra - 0x4;
+#endif
}
}
diff --git a/scripts/recordmcount.pl b/scripts/recordmcount.pl
index 2033af7..d44d55d 100755
--- a/scripts/recordmcount.pl
+++ b/scripts/recordmcount.pl
@@ -376,6 +376,11 @@
$mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s__mcount\$";
$type = ".quad";
$alignment = 8;
+} elsif ($arch eq "riscv") {
+ $function_regex = "^([0-9a-fA-F]+)\\s+<([^.0-9][0-9a-zA-Z_\\.]+)>:";
+ $mcount_regex = "^\\s*([0-9a-fA-F]+):\\sR_RISCV_CALL\\s_mcount\$";
+ $type = ".quad";
+ $alignment = 2;
} else {
die "Arch $arch is not supported with CONFIG_FTRACE_MCOUNT_RECORD";
}