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ad605bdad7
Indirect call instrumentation snippet uses x16 register in exit
handler to go to destination target
__bolt_instr_ind_call_handler_func:
msr nzcv, x1
ldp x0, x1, [sp], llvm#16
ldr x16, [sp], llvm#16
ldp x0, x1, [sp], llvm#16
br x16 <-----
This patch adds the instrumentation snippet by calling instrumentation
runtime library through indirect call instruction and adding the wrapper
to store/load target value and the register for original indirect instruction.
Example:
mov x16, foo
infirectCall:
adrp x8, Label
add x8, x8, #:lo12:Label
blr x8
Before:
Instrumented indirect call:
stp x0, x1, [sp, #-16]!
mov x0, x8
movk x1, #0x0, lsl llvm#48
movk x1, #0x0, lsl llvm#32
movk x1, #0x0, lsl llvm#16
movk x1, #0x0
stp x0, x1, [sp, #-16]!
adrp x0, __bolt_instr_ind_call_handler_func
add x0, x0, #:lo12:__bolt_instr_ind_call_handler_func
blr x0
__bolt_instr_ind_call_handler: (exit snippet)
msr nzcv, x1
ldp x0, x1, [sp], llvm#16
ldr x16, [sp], llvm#16
ldp x0, x1, [sp], llvm#16
br x16 <- overwrites the original value in X16
__bolt_instr_ind_call_handler_func: (entry snippet)
stp x0, x1, [sp, #-16]!
mrs x1, nzcv
adrp x0, __bolt_instr_ind_call_handler
add x0, x0, x0, #:lo12:__bolt_instr_ind_call_handler
ldr x0, [x0]
cmp x0, #0x0
b.eq __bolt_instr_ind_call_handler
str x30, [sp, #-16]!
blr x0 <--- runtime lib store/load all regs
ldr x30, [sp], llvm#16
b __bolt_instr_ind_call_handler
_________________________________________________________________________
After:
mov x16, foo
infirectCall:
adrp x8, Label
add x8, x8, #:lo12:Label
blr x8
Instrumented indirect call:
stp x0, x1, [sp, #-16]!
mov x0, x8
movk x1, #0x0, lsl llvm#48
movk x1, #0x0, lsl llvm#32
movk x1, #0x0, lsl llvm#16
movk x1, #0x0
stp x0, x30, [sp, #-16]!
adrp x8, __bolt_instr_ind_call_handler_func
add x8, x8, #:lo12:__bolt_instr_ind_call_handler_func
blr x8 <--- call trampoline instr lib
ldp x0, x30, [sp], llvm#16
mov x8, x0 <---- restore original target
ldp x0, x1, [sp], llvm#16
blr x8 <--- original indirect call instruction
// don't touch regs besides x0, x1
__bolt_instr_ind_call_handler: (exit snippet)
ret <---- return to original function with indirect call
__bolt_instr_ind_call_handler_func: (entry snippet)
adrp x0, __bolt_instr_ind_call_handler
add x0, x0, #:lo12:__bolt_instr_ind_call_handler
ldr x0, [x0]
cmp x0, #0x0
b.eq __bolt_instr_ind_call_handler
str x30, [sp, #-16]!
blr x0 <--- runtime lib store/load all regs
ldr x30, [sp], llvm#16
b __bolt_instr_ind_call_handler