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Commit bd7d38db authored by AKASHI Takahiro's avatar AKASHI Takahiro Committed by Will Deacon
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arm64: ftrace: Add dynamic ftrace support 



This patch allows "dynamic ftrace" if CONFIG_DYNAMIC_FTRACE is enabled.
Here we can turn on and off tracing dynamically per-function base.

On arm64, this is done by patching single branch instruction to _mcount()
inserted by gcc -pg option. The branch is replaced to NOP initially at
kernel start up, and later on, NOP to branch to ftrace_caller() when
enabled or branch to NOP when disabled.
Please note that ftrace_caller() is a counterpart of _mcount() in case of
'static' ftrace.

More details on architecture specific requirements are described in
Documentation/trace/ftrace-design.txt.

Acked-by: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarAKASHI Takahiro <takahiro.akashi@linaro.org>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent 819e50e2

arch/arm64/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -36,6 +36,7 @@ config ARM64 
	select HAVE_DMA_API_DEBUG

	select HAVE_DMA_ATTRS

	select HAVE_DMA_CONTIGUOUS

	select HAVE_DYNAMIC_FTRACE

	select HAVE_EFFICIENT_UNALIGNED_ACCESS

	select HAVE_FTRACE_MCOUNT_RECORD

	select HAVE_FUNCTION_TRACER

arch/arm64/include/asm/ftrace.h

+15 −0
Original line number Diff line number Diff line
@@ -18,6 +18,21 @@ 


#ifndef __ASSEMBLY__

extern void _mcount(unsigned long);



struct dyn_arch_ftrace {

	/* No extra data needed for arm64 */

};



extern unsigned long ftrace_graph_call;



static inline unsigned long ftrace_call_adjust(unsigned long addr)

{

	/*

	 * addr is the address of the mcount call instruction.

	 * recordmcount does the necessary offset calculation.

	 */

	return addr;

}

#endif /* __ASSEMBLY__ */



#endif /* __ASM_FTRACE_H */

arch/arm64/kernel/entry-ftrace.S

+43 −0
Original line number Diff line number Diff line
@@ -86,6 +86,7 @@ 
	add	\reg, \reg, #8

	.endm



#ifndef CONFIG_DYNAMIC_FTRACE

/*

 * void _mcount(unsigned long return_address)

 * @return_address: return address to instrumented function
@@ -134,6 +135,48 @@ skip_ftrace_call: 
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */

ENDPROC(_mcount)



#else /* CONFIG_DYNAMIC_FTRACE */

/*

 * _mcount() is used to build the kernel with -pg option, but all the branch

 * instructions to _mcount() are replaced to NOP initially at kernel start up,

 * and later on, NOP to branch to ftrace_caller() when enabled or branch to

 * NOP when disabled per-function base.

 */

ENTRY(_mcount)

	ret

ENDPROC(_mcount)



/*

 * void ftrace_caller(unsigned long return_address)

 * @return_address: return address to instrumented function

 *

 * This function is a counterpart of _mcount() in 'static' ftrace, and

 * makes calls to:

 *     - tracer function to probe instrumented function's entry,

 *     - ftrace_graph_caller to set up an exit hook

 */

ENTRY(ftrace_caller)

	mcount_enter



	mcount_get_pc0	x0		//     function's pc

	mcount_get_lr	x1		//     function's lr



	.global ftrace_call

ftrace_call:				// tracer(pc, lr);

	nop				// This will be replaced with "bl xxx"

					// where xxx can be any kind of tracer.



#ifdef CONFIG_FUNCTION_GRAPH_TRACER

	.global ftrace_graph_call

ftrace_graph_call:			// ftrace_graph_caller();

	nop				// If enabled, this will be replaced

					// "b ftrace_graph_caller"

#endif



	mcount_exit

ENDPROC(ftrace_caller)

#endif /* CONFIG_DYNAMIC_FTRACE */



ENTRY(ftrace_stub)

	ret

ENDPROC(ftrace_stub)

arch/arm64/kernel/ftrace.c

+112 −0
Original line number Diff line number Diff line
@@ -17,6 +17,87 @@ 
#include <asm/ftrace.h>

#include <asm/insn.h>



#ifdef CONFIG_DYNAMIC_FTRACE

/*

 * Replace a single instruction, which may be a branch or NOP.

 * If @validate == true, a replaced instruction is checked against 'old'.

 */

static int ftrace_modify_code(unsigned long pc, u32 old, u32 new,

			      bool validate)

{

	u32 replaced;



	/*

	 * Note:

	 * Due to modules and __init, code can disappear and change,

	 * we need to protect against faulting as well as code changing.

	 * We do this by aarch64_insn_*() which use the probe_kernel_*().

	 *

	 * No lock is held here because all the modifications are run

	 * through stop_machine().

	 */

	if (validate) {

		if (aarch64_insn_read((void *)pc, &replaced))

			return -EFAULT;



		if (replaced != old)

			return -EINVAL;

	}

	if (aarch64_insn_patch_text_nosync((void *)pc, new))

		return -EPERM;



	return 0;

}



/*

 * Replace tracer function in ftrace_caller()

 */

int ftrace_update_ftrace_func(ftrace_func_t func)

{

	unsigned long pc;

	u32 new;



	pc = (unsigned long)&ftrace_call;

	new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func, true);



	return ftrace_modify_code(pc, 0, new, false);

}



/*

 * Turn on the call to ftrace_caller() in instrumented function

 */

int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)

{

	unsigned long pc = rec->ip;

	u32 old, new;



	old = aarch64_insn_gen_nop();

	new = aarch64_insn_gen_branch_imm(pc, addr, true);



	return ftrace_modify_code(pc, old, new, true);

}



/*

 * Turn off the call to ftrace_caller() in instrumented function

 */

int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,

		    unsigned long addr)

{

	unsigned long pc = rec->ip;

	u32 old, new;



	old = aarch64_insn_gen_branch_imm(pc, addr, true);

	new = aarch64_insn_gen_nop();



	return ftrace_modify_code(pc, old, new, true);

}



int __init ftrace_dyn_arch_init(void)

{

	return 0;

}

#endif /* CONFIG_DYNAMIC_FTRACE */



#ifdef CONFIG_FUNCTION_GRAPH_TRACER

/*

 * function_graph tracer expects ftrace_return_to_handler() to be called
@@ -61,4 +142,35 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr, 
		return;

	}

}



#ifdef CONFIG_DYNAMIC_FTRACE

/*

 * Turn on/off the call to ftrace_graph_caller() in ftrace_caller()

 * depending on @enable.

 */

static int ftrace_modify_graph_caller(bool enable)

{

	unsigned long pc = (unsigned long)&ftrace_graph_call;

	u32 branch, nop;



	branch = aarch64_insn_gen_branch_imm(pc,

			(unsigned long)ftrace_graph_caller, false);

	nop = aarch64_insn_gen_nop();



	if (enable)

		return ftrace_modify_code(pc, nop, branch, true);

	else

		return ftrace_modify_code(pc, branch, nop, true);

}



int ftrace_enable_ftrace_graph_caller(void)

{

	return ftrace_modify_graph_caller(true);

}



int ftrace_disable_ftrace_graph_caller(void)

{

	return ftrace_modify_graph_caller(false);

}

#endif /* CONFIG_DYNAMIC_FTRACE */

#endif /* CONFIG_FUNCTION_GRAPH_TRACER */