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/*
* arch/arm64/kernel/entry-ftrace.S
*
* Copyright (C) 2013 Linaro Limited
* Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/linkage.h>
#include <asm/ftrace.h>
#include <asm/insn.h>
/*
* Gcc with -pg will put the following code in the beginning of each function:
* mov x0, x30
* bl _mcount
* [function's body ...]
* "bl _mcount" may be replaced to "bl ftrace_caller" or NOP if dynamic
* ftrace is enabled.
*
* Please note that x0 as an argument will not be used here because we can
* get lr(x30) of instrumented function at any time by winding up call stack
* as long as the kernel is compiled without -fomit-frame-pointer.
* (or CONFIG_FRAME_POINTER, this is forced on arm64)
*
* stack layout after mcount_enter in _mcount():
*
* current sp/fp => 0:+-----+
* in _mcount() | x29 | -> instrumented function's fp
* +-----+
* | x30 | -> _mcount()'s lr (= instrumented function's pc)
* old sp => +16:+-----+
* when instrumented | |
* function calls | ... |
* _mcount() | |
* | |
* instrumented => +xx:+-----+
* function's fp | x29 | -> parent's fp
* +-----+
* | x30 | -> instrumented function's lr (= parent's pc)
* +-----+
* | ... |
*/
.macro mcount_enter
stp x29, x30, [sp, #-16]!
mov x29, sp
.endm
.macro mcount_exit
ldp x29, x30, [sp], #16
ret
.endm
.macro mcount_adjust_addr rd, rn
sub \rd, \rn, #AARCH64_INSN_SIZE
.endm
/* for instrumented function's parent */
.macro mcount_get_parent_fp reg
ldr \reg, [x29]
ldr \reg, [\reg]
.endm
/* for instrumented function */
.macro mcount_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 mcount_get_lr reg
ldr \reg, [x29]
ldr \reg, [\reg, #8]
mcount_adjust_addr \reg, \reg
.endm
.macro mcount_get_lr_addr reg
ldr \reg, [x29]
add \reg, \reg, #8
.endm
#ifndef CONFIG_DYNAMIC_FTRACE
/*
* void _mcount(unsigned long return_address)
* @return_address: return address to instrumented function
*
* This function makes calls, if enabled, to:
* - tracer function to probe instrumented function's entry,
* - ftrace_graph_caller to set up an exit hook
*/
ENTRY(_mcount)
mcount_enter
ldr x0, =ftrace_trace_function
ldr x2, [x0]
adr x0, ftrace_stub
cmp x0, x2 // if (ftrace_trace_function
b.eq skip_ftrace_call // != ftrace_stub) {
mcount_get_pc x0 // function's pc
mcount_get_lr x1 // function's lr (= parent's pc)
blr x2 // (*ftrace_trace_function)(pc, lr);
#ifndef CONFIG_FUNCTION_GRAPH_TRACER
skip_ftrace_call: // return;
mcount_exit // }
#else
mcount_exit // return;
// }
skip_ftrace_call:
ldr x1, =ftrace_graph_return
ldr x2, [x1] // if ((ftrace_graph_return
cmp x0, x2 // != ftrace_stub)
b.ne ftrace_graph_caller
ldr x1, =ftrace_graph_entry // || (ftrace_graph_entry
ldr x2, [x1] // != ftrace_graph_entry_stub))
ldr x0, =ftrace_graph_entry_stub
cmp x0, x2
b.ne ftrace_graph_caller // ftrace_graph_caller();
mcount_exit
#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)
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
/*
* void ftrace_graph_caller(void)
*
* Called from _mcount() or ftrace_caller() when function_graph tracer is
* selected.
* This function w/ prepare_ftrace_return() fakes link register's value on
* the call stack in order to intercept instrumented function's return path
* and run return_to_handler() later on its exit.
*/
ENTRY(ftrace_graph_caller)
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
bl prepare_ftrace_return // prepare_ftrace_return(&lr, pc, fp)
mcount_exit
ENDPROC(ftrace_graph_caller)
/*
* void return_to_handler(void)
*
* Run ftrace_return_to_handler() before going back to parent.
* @fp is checked against the value passed by ftrace_graph_caller()
* only when CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST is enabled.
*/
ENTRY(return_to_handler)
str x0, [sp, #-16]!
mov x0, x29 // parent's fp
bl ftrace_return_to_handler// addr = ftrace_return_to_hander(fp);
mov x30, x0 // restore the original return address
ldr x0, [sp], #16
ret
END(return_to_handler)
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
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