This plumbs the option --gsframe through the various levels needed to support it in the assembler.

This is the final step in assembler-level sframe support for x86. With
it in place, clang produces sframe-sections that successfully link
with gnu-ld.

LLD support is pending some discussion.

Author: Sterling-Augustine

clang/include/clang/Basic/CodeGenOptions.def

@@ -120,6 +120,8 @@ CODEGENOPT(StackSizeSection  , 1, 0, Benign) ///< Set when -fstack-size-section
 ///< Set when -femit-compact-unwind-non-canonical is enabled.
 CODEGENOPT(EmitCompactUnwindNonCanonical, 1, 0, Benign)
 
+CODEGENOPT(EmitSFrameUnwind, 1, 0, Benign) ///< Set when -sframe is enabled.
+
 ///< Set when -fxray-always-emit-customevents is enabled.
 CODEGENOPT(XRayAlwaysEmitCustomEvents , 1, 0, Benign)
 

clang/include/clang/Driver/Options.td

@@ -7729,6 +7729,11 @@ def massembler_fatal_warnings : Flag<["-"], "massembler-fatal-warnings">,
 def crel : Flag<["--"], "crel">,
   HelpText<"Enable CREL relocation format (ELF only)">,
   MarshallingInfoFlag<CodeGenOpts<"Crel">>;
+// The leading 'g' is misleading. This is an unwind tables option, not
+// a debug option. But uses this name for gnu compatibility.
+def gsframe : Flag<["--"], "gsframe">,
+              HelpText<"Generate .sframe unwind sections (ELF only)">,
+              MarshallingInfoFlag<CodeGenOpts<"EmitSFrameUnwind">>;
 def mmapsyms_implicit : Flag<["-"], "mmapsyms=implicit">,
   HelpText<"Allow mapping symbol at section beginning to be implicit, "
     "lowering number of mapping symbols at the expense of some "

clang/lib/CodeGen/BackendUtil.cpp

@@ -500,6 +500,7 @@ static bool initTargetOptions(const CompilerInstance &CI,
   Options.MCOptions.EmitDwarfUnwind = CodeGenOpts.getEmitDwarfUnwind();
   Options.MCOptions.EmitCompactUnwindNonCanonical =
       CodeGenOpts.EmitCompactUnwindNonCanonical;
+  Options.MCOptions.EmitSFrameUnwind = CodeGenOpts.EmitSFrameUnwind;
   Options.MCOptions.MCRelaxAll = CodeGenOpts.RelaxAll;
   Options.MCOptions.MCSaveTempLabels = CodeGenOpts.SaveTempLabels;
   Options.MCOptions.MCUseDwarfDirectory =

clang/lib/Driver/ToolChains/Clang.cpp

@@ -2626,6 +2626,14 @@ static void CollectArgsForIntegratedAssembler(Compilation &C,
                                   llvm::codegenoptions::DebugInfoConstructor,
                                   DwarfVersion, llvm::DebuggerKind::Default);
         }
+      } else if (Value == "--gsframe") {
+        if (Triple.isOSBinFormatELF() && Triple.isX86()) {
+          CmdArgs.push_back("--gsframe");
+        } else {
+          D.Diag(diag::err_drv_unsupported_opt_for_target)
+              << Value << D.getTargetTriple();
+          break;
+        }
       } else if (Value.starts_with("-mcpu") || Value.starts_with("-mfpu") ||
                  Value.starts_with("-mhwdiv") || Value.starts_with("-march")) {
         // Do nothing, we'll validate it later.
@@ -5929,6 +5937,16 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   else if (UnwindTables)
      CmdArgs.push_back("-funwind-tables=1");
 
+  // Sframe unwind tables are independent of the other types, and only defined
+  // for these two targets.
+  if (Arg *A = Args.getLastArg(options::OPT_gsframe)) {
+    if ((Triple.isAArch64() || Triple.isX86()) && Triple.isOSBinFormatELF())
+      CmdArgs.push_back("--gsframe");
+    else
+      D.Diag(diag::err_drv_unsupported_opt_for_target)
+          << A->getOption().getName() << TripleStr;
+  }
+
   // Prepare `-aux-target-cpu` and `-aux-target-feature` unless
   // `--gpu-use-aux-triple-only` is specified.
   if (!Args.getLastArg(options::OPT_gpu_use_aux_triple_only) &&

clang/test/Driver/sframe.c

@@ -0,0 +1,15 @@
+// RUN: %clang -### -c --target=x86_64 -Wa,--gsframe %s -Werror 2>&1 | FileCheck %s
+// CHECK:  "-cc1" {{.*}}"--gsframe"
+
+// RUN: %clang -### -c --target=x86_64 %s 2>&1 | FileCheck %s --check-prefix=NO
+// NO:     "-cc1"
+
+// RUN: %clang -### -c --target=x86_64 -Werror -Wa,--gsframe -x assembler %s -Werror 2>&1 | FileCheck %s --check-prefix=ASM
+// ASM:    "-cc1as" {{.*}}"--gsframe"
+
+// RUN: not %clang -### -c --target=mips64 -Wa,--gsframe %s 2>&1 | FileCheck %s --check-prefix=NOTARGETC
+// NOTARGETC: error: unsupported option '--gsframe' for target '{{.*}}'
+
+// RUN: not %clang -### -c --target=mips64 -Wa,--gsframe -x assembler %s 2>&1 | FileCheck %s --check-prefix=NOTARGETASM
+// NOTARGETASM: error: unsupported option '--gsframe' for target '{{.*}}'
+

clang/test/Misc/cc1as-sframe.s

@@ -0,0 +1,8 @@
+// REQUIRES: x86-registered-target
+// RUN: %clang -cc1as -triple x86_64 %s -filetype obj --gsframe -o %t.o
+// RUN: llvm-readelf -S %t.o | FileCheck %s
+
+// CHECK: .sframe
+.cfi_startproc
+        call foo
+.cfi_endproc

clang/tools/driver/cc1as_main.cpp

@@ -163,6 +163,10 @@ struct AssemblerInvocation {
   LLVM_PREFERRED_TYPE(bool)
   unsigned EmitCompactUnwindNonCanonical : 1;
 
+  // Whether to emit sframe unwind sections.
+  LLVM_PREFERRED_TYPE(bool)
+  unsigned EmitSFrameUnwind : 1;
+
   LLVM_PREFERRED_TYPE(bool)
   unsigned Crel : 1;
   LLVM_PREFERRED_TYPE(bool)
@@ -388,6 +392,7 @@ bool AssemblerInvocation::CreateFromArgs(AssemblerInvocation &Opts,
 
   Opts.EmitCompactUnwindNonCanonical =
       Args.hasArg(OPT_femit_compact_unwind_non_canonical);
+  Opts.EmitSFrameUnwind = Args.hasArg(OPT_gsframe);
   Opts.Crel = Args.hasArg(OPT_crel);
   Opts.ImplicitMapsyms = Args.hasArg(OPT_mmapsyms_implicit);
   Opts.X86RelaxRelocations = !Args.hasArg(OPT_mrelax_relocations_no);
@@ -450,6 +455,7 @@ static bool ExecuteAssemblerImpl(AssemblerInvocation &Opts,
   MCOptions.MCRelaxAll = Opts.RelaxAll;
   MCOptions.EmitDwarfUnwind = Opts.EmitDwarfUnwind;
   MCOptions.EmitCompactUnwindNonCanonical = Opts.EmitCompactUnwindNonCanonical;
+  MCOptions.EmitSFrameUnwind = Opts.EmitSFrameUnwind;
   MCOptions.MCSaveTempLabels = Opts.SaveTemporaryLabels;
   MCOptions.Crel = Opts.Crel;
   MCOptions.ImplicitMapSyms = Opts.ImplicitMapsyms;