From e02e9582d253ffaa04c9137f732efb0b80f98907 Mon Sep 17 00:00:00 2001 From: Jacob Bramley Date: Wed, 19 Jan 2022 14:51:59 +0000 Subject: [PATCH] Use error-on-mismatch policy for PAuth module flags. This agrees with Clang, and avoids an error when using LTO with mixed C/Rust. LLVM considers different behaviour flags to be a mismatch, even when the flag value itself is the same. This also makes the flag setting explicit for all uses of LLVMRustAddModuleFlag. --- compiler/rustc_codegen_llvm/src/context.rs | 31 ++++++++++++++----- .../rustc_codegen_llvm/src/debuginfo/mod.rs | 15 +++++++-- compiler/rustc_codegen_llvm/src/llvm/ffi.rs | 31 ++++++++++++++++++- .../rustc_llvm/llvm-wrapper/RustWrapper.cpp | 9 ++++-- 4 files changed, 73 insertions(+), 13 deletions(-) diff --git a/compiler/rustc_codegen_llvm/src/context.rs b/compiler/rustc_codegen_llvm/src/context.rs index bb16bc5dccdfc..8672459b5da3a 100644 --- a/compiler/rustc_codegen_llvm/src/context.rs +++ b/compiler/rustc_codegen_llvm/src/context.rs @@ -215,16 +215,19 @@ pub unsafe fn create_module<'ll>( // to ensure intrinsic calls don't use it. if !sess.needs_plt() { let avoid_plt = "RtLibUseGOT\0".as_ptr().cast(); - llvm::LLVMRustAddModuleFlag(llmod, avoid_plt, 1); + llvm::LLVMRustAddModuleFlag(llmod, llvm::LLVMModFlagBehavior::Warning, avoid_plt, 1); } if sess.is_sanitizer_cfi_enabled() { // FIXME(rcvalle): Add support for non canonical jump tables. let canonical_jump_tables = "CFI Canonical Jump Tables\0".as_ptr().cast(); - // FIXME(rcvalle): Add it with Override behavior flag--LLVMRustAddModuleFlag adds it with - // Warning behavior flag. Add support for specifying the behavior flag to - // LLVMRustAddModuleFlag. - llvm::LLVMRustAddModuleFlag(llmod, canonical_jump_tables, 1); + // FIXME(rcvalle): Add it with Override behavior flag. + llvm::LLVMRustAddModuleFlag( + llmod, + llvm::LLVMModFlagBehavior::Warning, + canonical_jump_tables, + 1, + ); } // Control Flow Guard is currently only supported by the MSVC linker on Windows. @@ -233,11 +236,21 @@ pub unsafe fn create_module<'ll>( CFGuard::Disabled => {} CFGuard::NoChecks => { // Set `cfguard=1` module flag to emit metadata only. - llvm::LLVMRustAddModuleFlag(llmod, "cfguard\0".as_ptr() as *const _, 1) + llvm::LLVMRustAddModuleFlag( + llmod, + llvm::LLVMModFlagBehavior::Warning, + "cfguard\0".as_ptr() as *const _, + 1, + ) } CFGuard::Checks => { // Set `cfguard=2` module flag to emit metadata and checks. - llvm::LLVMRustAddModuleFlag(llmod, "cfguard\0".as_ptr() as *const _, 2) + llvm::LLVMRustAddModuleFlag( + llmod, + llvm::LLVMModFlagBehavior::Warning, + "cfguard\0".as_ptr() as *const _, + 2, + ) } } } @@ -247,24 +260,28 @@ pub unsafe fn create_module<'ll>( llvm::LLVMRustAddModuleFlag( llmod, + llvm::LLVMModFlagBehavior::Error, "branch-target-enforcement\0".as_ptr().cast(), bti.into(), ); llvm::LLVMRustAddModuleFlag( llmod, + llvm::LLVMModFlagBehavior::Error, "sign-return-address\0".as_ptr().cast(), pac.is_some().into(), ); let pac_opts = pac.unwrap_or(PacRet { leaf: false, key: PAuthKey::A }); llvm::LLVMRustAddModuleFlag( llmod, + llvm::LLVMModFlagBehavior::Error, "sign-return-address-all\0".as_ptr().cast(), pac_opts.leaf.into(), ); let is_bkey = if pac_opts.key == PAuthKey::A { false } else { true }; llvm::LLVMRustAddModuleFlag( llmod, + llvm::LLVMModFlagBehavior::Error, "sign-return-address-with-bkey\0".as_ptr().cast(), is_bkey.into(), ); diff --git a/compiler/rustc_codegen_llvm/src/debuginfo/mod.rs b/compiler/rustc_codegen_llvm/src/debuginfo/mod.rs index 61e49fab6ff88..28eb8e2a0a462 100644 --- a/compiler/rustc_codegen_llvm/src/debuginfo/mod.rs +++ b/compiler/rustc_codegen_llvm/src/debuginfo/mod.rs @@ -108,18 +108,29 @@ impl<'a, 'tcx> CrateDebugContext<'a, 'tcx> { // This can be overridden using --llvm-opts -dwarf-version,N. // Android has the same issue (#22398) if let Some(version) = sess.target.dwarf_version { - llvm::LLVMRustAddModuleFlag(self.llmod, "Dwarf Version\0".as_ptr().cast(), version) + llvm::LLVMRustAddModuleFlag( + self.llmod, + llvm::LLVMModFlagBehavior::Warning, + "Dwarf Version\0".as_ptr().cast(), + version, + ) } // Indicate that we want CodeView debug information on MSVC if sess.target.is_like_msvc { - llvm::LLVMRustAddModuleFlag(self.llmod, "CodeView\0".as_ptr().cast(), 1) + llvm::LLVMRustAddModuleFlag( + self.llmod, + llvm::LLVMModFlagBehavior::Warning, + "CodeView\0".as_ptr().cast(), + 1, + ) } // Prevent bitcode readers from deleting the debug info. let ptr = "Debug Info Version\0".as_ptr(); llvm::LLVMRustAddModuleFlag( self.llmod, + llvm::LLVMModFlagBehavior::Warning, ptr.cast(), llvm::LLVMRustDebugMetadataVersion(), ); diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs index a1c7d2b4f6156..2b10218879038 100644 --- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs +++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs @@ -61,6 +61,26 @@ pub enum LLVMMachineType { ARM = 0x01c0, } +/// LLVM's Module::ModFlagBehavior, defined in llvm/include/llvm/IR/Module.h. +/// +/// When merging modules (e.g. during LTO), their metadata flags are combined. Conflicts are +/// resolved according to the merge behaviors specified here. Flags differing only in merge +/// behavior are still considered to be in conflict. +/// +/// In order for Rust-C LTO to work, we must specify behaviors compatible with Clang. Notably, +/// 'Error' and 'Warning' cannot be mixed for a given flag. +#[derive(Copy, Clone, PartialEq)] +#[repr(C)] +pub enum LLVMModFlagBehavior { + Error = 1, + Warning = 2, + Require = 3, + Override = 4, + Append = 5, + AppendUnique = 6, + Max = 7, +} + // Consts for the LLVM CallConv type, pre-cast to usize. /// LLVM CallingConv::ID. Should we wrap this? @@ -1895,7 +1915,16 @@ extern "C" { pub fn LLVMRustIsRustLLVM() -> bool; - pub fn LLVMRustAddModuleFlag(M: &Module, name: *const c_char, value: u32); + /// Add LLVM module flags. + /// + /// In order for Rust-C LTO to work, module flags must be compatible with Clang. What + /// "compatible" means depends on the merge behaviors involved. + pub fn LLVMRustAddModuleFlag( + M: &Module, + merge_behavior: LLVMModFlagBehavior, + name: *const c_char, + value: u32, + ); pub fn LLVMRustMetadataAsValue<'a>(C: &'a Context, MD: &'a Metadata) -> &'a Value; diff --git a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp index c21e4acbefec0..dcd6327c92f6a 100644 --- a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp +++ b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp @@ -722,9 +722,12 @@ extern "C" bool LLVMRustIsRustLLVM() { #endif } -extern "C" void LLVMRustAddModuleFlag(LLVMModuleRef M, const char *Name, - uint32_t Value) { - unwrap(M)->addModuleFlag(Module::Warning, Name, Value); +extern "C" void LLVMRustAddModuleFlag( + LLVMModuleRef M, + Module::ModFlagBehavior MergeBehavior, + const char *Name, + uint32_t Value) { + unwrap(M)->addModuleFlag(MergeBehavior, Name, Value); } extern "C" LLVMValueRef LLVMRustMetadataAsValue(LLVMContextRef C, LLVMMetadataRef MD) {