RCTProfileTrampoline-arm.S
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/**
* Copyright (c) 2015-present, Facebook, Inc.
* All rights reserved.
*
* This source code is licensed under the BSD-style license found in the
* LICENSE file in the root directory of this source tree. An additional grant
* of patent rights can be found in the PATENTS file in the same directory.
*/
#include "RCTDefines.h"
#include "RCTMacros.h"
#if RCT_PROFILE && defined(__arm__)
.thumb
.thumb_func
.globl SYMBOL_NAME(RCTProfileTrampoline)
SYMBOL_NAME(RCTProfileTrampoline):
/**
* The explanation here is shorter, refer to the x86_64 implementation to a
* richer explanation
*/
/**
* Save the parameter registers (r0-r3), r7 (frame pointer) and lr (link
* register (contains the address of the caller of RCTProfileTrampoline)
*/
push {r0-r3, r7, lr}
/**
* Allocate memory to store values across function calls: 12-bytes are
* allocated to store 3 values: the previous value of the callee saved
* register used to save the pointer to the allocated memory, the caller of
* RCTProfileTrampoline and the address of the actual function we want to
* profile
*/
mov r0, #0xc
bl SYMBOL_NAME(RCTProfileMalloc)
/**
* r4 is the callee saved register we'll use to refer to the allocated memory,
* store its initial value, so we can restore it later
*/
str r4, [r0]
mov r4, r0
/**
* void RCTProfileGetImplementation(id object, SEL selector) in RCTProfile.m
*
* Load the first 2 argumenters (self and _cmd) used to call
* RCTProfileTrampoline from the stack and put them on the appropriate registers.
*/
ldr r0, [sp]
ldr r1, [sp, #0x4]
bl SYMBOL_NAME(RCTProfileGetImplementation)
// store the actual function address in the allocated memory
str r0, [r4, #0x4]
/**
* void RCTProfileGetImplementation(id object, SEL selector) in RCTProfile.m
*
* Load the first 2 arguments again to start the profiler
*/
ldr r0, [sp]
ldr r1, [sp, #0x4]
bl SYMBOL_NAME(RCTProfileTrampolineStart)
/**
* Restore the state to call the actual function we want to profile: pop
* all the registers
*/
pop {r0-r3, r7, lr}
// store lr (the caller) since it'll be overridden by `blx` (call)
str lr, [r4, #0x8]
ldr r12, [r4, #0x4] // load the function address
blx r12 // call it
push {r0} // save return value
// void RCTProfileTrampolineEnd(void) in RCTProfile.m - just ends this profile
bl SYMBOL_NAME(RCTProfileTrampolineEnd)
/**
* Save the value we still need from the allocated memory (caller address),
* restore r4 and free the allocated memory (put its address in r0)
*/
mov r0, r4
ldr r1, [r4, #0x8]
ldr r4, [r4]
push {r1} // save the caller on the stack
bl SYMBOL_NAME(RCTProfileFree)
pop {lr} // pop the caller
pop {r0} // pop the return value
bx lr // jump to the calleer
trap
#endif