[clang] [Driver, sanitizer] Remove RequiresPIE and msan's RequiresPIE setting (PR #77689)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-driver

Author: Fangrui Song (MaskRay)

<details>
<summary>Changes</summary>

This variable causes clang to default to -fPIE when no PIC/PIC option is
specified.

msan used to require PIE because many `kMemoryLayout` made the low
address (used by ET_EXEC executables) invalid. Current msan.h no longer
does so, rendering this PIE requirement unneeded. The same argument
applies to -fsanitize=dataflow.

On Linux, most builds set CLANG_DEFAULT_PIE_ON_LINUX to 1, making
`RequiresPIE/NeedPIE` redundant on Linux.

(`NeedPIE` is not removed for now due to the -fsanitize-cfi-cross-dso
comment. If it's indeed incompatible with explicit -fno-pic, a warning
is probably better.)


---
Full diff: https://github.com/llvm/llvm-project/pull/77689.diff


1 Files Affected:

- (modified) clang/lib/Driver/SanitizerArgs.cpp (+1-7) 


``````````diff
diff --git a/clang/lib/Driver/SanitizerArgs.cpp b/clang/lib/Driver/SanitizerArgs.cpp
index ad68c086b71790..9d6ea371f9f6dd 100644
--- a/clang/lib/Driver/SanitizerArgs.cpp
+++ b/clang/lib/Driver/SanitizerArgs.cpp
@@ -39,8 +39,6 @@ static const SanitizerMask NotAllowedWithTrap = SanitizerKind::Vptr;
 static const SanitizerMask NotAllowedWithMinimalRuntime = SanitizerKind::Vptr;
 static const SanitizerMask NotAllowedWithExecuteOnly =
     SanitizerKind::Function | SanitizerKind::KCFI;
-static const SanitizerMask RequiresPIE =
-    SanitizerKind::DataFlow | SanitizerKind::Scudo;
 static const SanitizerMask NeedsUnwindTables =
     SanitizerKind::Address | SanitizerKind::HWAddress | SanitizerKind::Thread |
     SanitizerKind::Memory | SanitizerKind::DataFlow;
@@ -303,9 +301,7 @@ bool SanitizerArgs::needsCfiDiagRt() const {
          CfiCrossDso && !ImplicitCfiRuntime;
 }
 
-bool SanitizerArgs::requiresPIE() const {
-  return NeedPIE || (Sanitizers.Mask & RequiresPIE);
-}
+bool SanitizerArgs::requiresPIE() const { return NeedPIE; }
 
 bool SanitizerArgs::needsUnwindTables() const {
   return static_cast<bool>(Sanitizers.Mask & NeedsUnwindTables);
@@ -699,8 +695,6 @@ SanitizerArgs::SanitizerArgs(const ToolChain &TC,
     MsanParamRetval = Args.hasFlag(
         options::OPT_fsanitize_memory_param_retval,
         options::OPT_fno_sanitize_memory_param_retval, MsanParamRetval);
-    NeedPIE |= !(TC.getTriple().isOSLinux() &&
-                 TC.getTriple().getArch() == llvm::Triple::x86_64);
   } else if (AllAddedKinds & SanitizerKind::KernelMemory) {
     MsanUseAfterDtor = false;
     MsanParamRetval = Args.hasFlag(

``````````

</details>


https://github.com/llvm/llvm-project/pull/77689