[Driver] Pass --fix-cortex-a53-843419 automatically on Fuchsia

[phosek]

Summary

When targeting cortex-a53, set this linker flag rather than relying
on the toolchain users to do it in their build.

[mcgrathr]

clang/lib/Driver/ToolChains/Fuchsia.cpp

91

How does this relate to -march, -mtune, and/or -mcpu?
It's not at all clear to me how we discern automatically when a A53 might be included in the supported target CPU set. I'm not entirely sure we should have automatic injection in some cases where A53 is a valid target but not all. That is, if some compiler option combinations that produce code meant to be compatible with an A53 won't automatically get the --fix option, then perhaps it's better to require the explicit --fix option when supporting A53 is the explicit intent.

[phosek]

clang/lib/Driver/ToolChains/Fuchsia.cpp

91

This is the same logic as used by the Gnu driver. getCPUName only considers -mcpu, it ignores -march and -mtune as far as I can tell.

[mcgrathr]

clang/lib/Driver/ToolChains/Fuchsia.cpp

91

If the empty or "generic" case is what will apply when no -mcpu switch is given regardless of -march then I guess this is adequate since we're not really concerned with any architectures older than A53 where someone might use -mcpu=... as a proxy for "X and later" where X<A53.

I think this area needs to be more clearly specified and documented eventually, however. Ideally the determinant would whether the combination of -march and/or -mcpu switches indicates generating code that is compatible with an A53 CPU, since only if running on an A53 is ruled out should we omit the erratum workaround.

clang/lib/Driver/ToolChains/Fuchsia.cpp

void fuchsia::Linker::ConstructJob(Compilation &C, const JobAction &JA,
                                    const InputInfo &Output,
                                    const InputInfoList &Inputs,
                                    const ArgList &Args,
                                    const char *LinkingOutput) const {
   const toolchains::Fuchsia &ToolChain =
       static_cast<const toolchains::Fuchsia &>(getToolChain());
   const Driver &D = ToolChain.getDriver();
 
+  const llvm::Triple &Triple = ToolChain.getEffectiveTriple();
+
   ArgStringList CmdArgs;
 
   // Silence warning for "clang -g foo.o -o foo"
   Args.ClaimAllArgs(options::OPT_g_Group);
   // and "clang -emit-llvm foo.o -o foo"
   Args.ClaimAllArgs(options::OPT_emit_llvm);
   // and for "clang -w foo.o -o foo". Other warning options are already
   // handled somewhere else.
void fuchsia::Linker::ConstructJob(Compilation &C, const JobAction &JA,
 
   if (Args.hasArg(options::OPT_r)) {
     CmdArgs.push_back("-r");
   } else {
     CmdArgs.push_back("--build-id");
     CmdArgs.push_back("--hash-style=gnu");
   }
 
+  if (ToolChain.getArch() == llvm::Triple::aarch64) {
+    std::string CPU = getCPUName(D, Args, Triple);
+    if (CPU.empty() || CPU == "generic" || CPU == "cortex-a53")
+      CmdArgs.push_back("--fix-cortex-a53-843419");
+  }
+
   CmdArgs.push_back("--eh-frame-hdr");
 
   if (Args.hasArg(options::OPT_static))
     CmdArgs.push_back("-Bstatic");
   else if (Args.hasArg(options::OPT_shared))
     CmdArgs.push_back("-shared");
 
   const SanitizerArgs &SanArgs = ToolChain.getSanitizerArgs(Args);

clang/test/Driver/fuchsia.c

 // CHECK: "-stack-protector" "2"
 // CHECK-AARCH64: "-target-feature" "+outline-atomics"
 // CHECK-NOT: "-fcommon"
 // CHECK: {{.*}}ld.lld{{.*}}" "-z" "max-page-size=4096" "-z" "now" "-z" "rodynamic" "-z" "separate-loadable-segments" "-z" "rel" "--pack-dyn-relocs=relr"
 // CHECK: "--sysroot=[[SYSROOT]]"
 // CHECK: "-pie"
 // CHECK: "--build-id"
 // CHECK: "--hash-style=gnu"
+// CHECK-AARCH64: "--fix-cortex-a53-843419"
 // CHECK: "-dynamic-linker" "ld.so.1"
 // CHECK: Scrt1.o
 // CHECK-NOT: crti.o
 // CHECK-NOT: crtbegin.o
 // CHECK: "-L[[SYSROOT]]{{/|\\\\}}lib"
 // CHECK-X86_64: "[[RESOURCE_DIR]]{{/|\\\\}}lib{{/|\\\\}}x86_64-unknown-fuchsia{{/|\\\\}}libclang_rt.builtins.a"
 // CHECK-AARCH64: "[[RESOURCE_DIR]]{{/|\\\\}}lib{{/|\\\\}}aarch64-unknown-fuchsia{{/|\\\\}}libclang_rt.builtins.a"
 // CHECK-RISCV64: "[[RESOURCE_DIR]]{{/|\\\\}}lib{{/|\\\\}}riscv64-unknown-fuchsia{{/|\\\\}}libclang_rt.builtins.a"