[PATCH] D138757: [zero-call-used-regs] Mark only non-debug instruction's register as used

[Shivam Gupta via Phabricator via llvm-commits]

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zero-call-used-regs pass generate an xor instruction to help mitigate
return-oriented programming exploits via zeroing out used registers. But
in this below test case with -g option there is dbg.value instruction
associating the register with the debug-info description of the formal
parameter d, which makes the register appear used, therefore it zero the
register edi in -g case and makes binary different from without -g option.

The pass should be looking only at the non-debug uses.

$ cat test.c
char a[];
int b;
__attribute__((zero_call_used_regs("used"))) char c(int d) {

  *a = ({
    int e = d;
    b;
  });

}


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D138757

Files:
  llvm/lib/CodeGen/PrologEpilogInserter.cpp


Index: llvm/lib/CodeGen/PrologEpilogInserter.cpp
===================================================================
--- llvm/lib/CodeGen/PrologEpilogInserter.cpp
+++ llvm/lib/CodeGen/PrologEpilogInserter.cpp
@@ -1234,6 +1234,9 @@
           if (!MO.isReg())
             continue;
 
+          if (MI.isDebugInstr())
+            continue;
+
           MCRegister Reg = MO.getReg();
           if (AllocatableSet[Reg] && !MO.isImplicit() &&
               (MO.isDef() || MO.isUse()))


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