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Unverified Commit 1cead2d7 authored by Palmer Dabbelt's avatar Palmer Dabbelt
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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.
parents 0adb3285 b785ec12

arch/riscv/Kconfig

+3 −0
Original line number Diff line number Diff line
@@ -114,6 +114,9 @@ config ARCH_RV64I 
	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

arch/riscv/Makefile

+3 −0
Original line number Diff line number Diff line
@@ -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

arch/riscv/include/asm/ftrace.h

+56 −0
Original line number Diff line number Diff line
@@ -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

arch/riscv/kernel/Makefile

+3 −2
Original line number Diff line number Diff line
@@ -34,7 +34,8 @@ CFLAGS_setup.o := -mcmodel=medany 
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:

arch/riscv/kernel/ftrace.c

+173 −2
Original line number Diff line number Diff line
@@ -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;



	/*

 * Most of this file is copied from arm64.

	 * 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 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 */