Use linker flag --fix-cortex-a53-843419 on Android ARM64 compilation.

[srhines]

Summary

This is only forced on if there is no non-Cortex-A53 CPU specified as
well. Android's platform and NDK builds need to assume that the code can
be run on Cortex-A53 devices, so we always enable the fix unless we know
specifically that the code is only running on a different kind of CPU.

[jmolloy]

LGTM.

[srhines]

From what I can tell, there is no nice way to generate tests for Clang's driver when producing linker flags. -### only works for the -cc1 command line (which won't see this flag, since it is only for linking, and not compilation). If there is a suggestion for how to automatically test this, I am listening, but all my local tests looked fine (for generating/suppressing the flag). :)

[rengolin]

In D25761#573892, @srhines wrote:

From what I can tell, there is no nice way to generate tests for Clang's driver when producing linker flags. -### only works for the -cc1 command line (which won't see this flag, since it is only for linking, and not compilation). If there is a suggestion for how to automatically test this, I am listening, but all my local tests looked fine (for generating/suppressing the flag). :)

I think "clang -v" will show the linker invocation, with all its flags.

[srhines]

In D25761#573902, @rengolin wrote:

In D25761#573892, @srhines wrote:

From what I can tell, there is no nice way to generate tests for Clang's driver when producing linker flags. -### only works for the -cc1 command line (which won't see this flag, since it is only for linking, and not compilation). If there is a suggestion for how to automatically test this, I am listening, but all my local tests looked fine (for generating/suppressing the flag). :)

I think "clang -v" will show the linker invocation, with all its flags.

But is there a way to get a dry-run of the linker? I don't want to run /usr/bin/ld for ARM targets. It seems like all of the other linker flag-related tests in tests/Driver/ only work for x86.

[rengolin]

In D25761#573903, @srhines wrote:

I think "clang -v" will show the linker invocation, with all its flags.

But is there a way to get a dry-run of the linker? I don't want to run /usr/bin/ld for ARM targets. It seems like all of the other linker flag-related tests in tests/Driver/ only work for x86.

I think the combination of -v and -### does that, no?

[srhines]

Added a test for this behavior.

I missed that "-### -v" was actually working correctly last night. Tests added
so I am more satisfied that this won't break accidentally in the future.

lib/Driver/Tools.cpp

if (Args.hasArg(options::OPT_rdynamic))
     CmdArgs.push_back("-export-dynamic");
 
   if (Args.hasArg(options::OPT_s))
     CmdArgs.push_back("-s");
 
   if (Arch == llvm::Triple::armeb || Arch == llvm::Triple::thumbeb)
     arm::appendEBLinkFlags(Args, CmdArgs, Triple);
 
+  // Most Android ARM64 targets should enable the linker fix for erratum
+  // 843419. Only non-Cortex-A53 devices are allowed to skip this flag.
+  if (Arch == llvm::Triple::aarch64 && isAndroid) {
+    std::string CPU = getCPUName(Args, Triple);
+    if (CPU.empty() || CPU == "generic" || CPU == "cortex-a53")
+      CmdArgs.push_back("--fix-cortex-a53-843419");
+  }
+
   for (const auto &Opt : ToolChain.ExtraOpts)
     CmdArgs.push_back(Opt.c_str());
 
   if (!Args.hasArg(options::OPT_static)) {
     CmdArgs.push_back("--eh-frame-hdr");
   }
 
   CmdArgs.push_back("-m");