[PATCH] D120362: [sanitizer][sancov] Refactor GetNextInstructionPc/GetPreviousInstructionPc

[Xiaodong Liu via Phabricator via llvm-commits]

XiaodongLoong added a comment.

> For sancov, `getPreviousInstructionPc` does not use the `PC - 8` code path for
> Sparc. Triple.h does not have isSparc yet and I hope someone can investigate
> why Mips/Sparc use the weird -8.

@MaskRay
IMO, The SPARC and MIPS branching operations have a branch delay slot, 4 more bytes occupied.
I did an experiment on MIPS64EL machine as following:

  // cat caller.c 
  void foo() {
  	void *caller_pc = __builtin_return_address(0);
  }
  
  int main() {
  	foo();
  }

Debug with gdb:

  print caller_pc variable : 
  (gdb) p caller_pc
  $1 = (void *) 0x555555554b54 <main+48>
  
  Dump of assembler code for function main:
  ...
     0x0000555555554b38 <+20>:	lui	gp,0x2
     0x0000555555554b3c <+24>:	daddiu	gp,gp,-32340
     0x0000555555554b40 <+28>:	daddu	gp,gp,t9
  => 0x0000555555554b44 <+32>:	ld	v0,-32680(gp)
     0x0000555555554b48 <+36>:	move	t9,v0
     0x0000555555554b4c <+40>:	bal	0x555555554af0 <foo>   /// caller_pc - 8
     0x0000555555554b50 <+44>:	nop                            /// caller_pc - 4
     0x0000555555554b54 <+48>:	move	v0,zero                /// caller_pc
     0x0000555555554b58 <+52>:	move	sp,s8
  ...


Repository:
  rG LLVM Github Monorepo

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https://reviews.llvm.org/D120362