[Driver] Render target options (e.g. -fuse-init-array) for -fembed-bitcode

[MaskRay]

Summary

Modern ELF platforms use -fuse-init-array to emit .init_array instead of
.ctors . ld.bfd and gold --ctors-in-init-array merge .init_array and
.ctors into .init_array but lld doesn't do that.

If crtbegin*.o crtend*.o don't provide .ctors/.dtors, such .ctors in
user object files can lead to crash (see PR42002. The first and the last
elements in .ctors/.dtors are ignored - they are traditionally provided
by crtbegin*.o crtend*.o).

Call addClangTargetOptions() to ensure -fuse-init-array is rendered on
modern ELF platforms. On Hexagon, this renders -target-feature
+reserved-r19 for -ffixed-r19.

[compnerd]

lib/Driver/ToolChains/Clang.cpp

3670

Hmm, what other arguments will this render into the option handling that we weren't handling before?

[MaskRay]

lib/Driver/ToolChains/Clang.cpp

3670

-fuse-init-array is the only one on Linux x86. Other OSes/targets may have more, e.g. Hexagon has:

void HexagonToolChain::addClangTargetOptions(const ArgList &DriverArgs,

                                           ArgStringList &CC1Args,
                                           Action::OffloadKind) const {
if (DriverArgs.hasArg(options::OPT_ffixed_r19)) {
  CC1Args.push_back("-target-feature");
  CC1Args.push_back("+reserved-r19");
}
if (isAutoHVXEnabled(DriverArgs)) {
  CC1Args.push_back("-mllvm");
  CC1Args.push_back("-hexagon-autohvx");
}

}

NetBSD has a -D (it should not matter):

void NetBSD::addClangTargetOptions(const ArgList &,

                                 ArgStringList &CC1Args,
                                 Action::OffloadKind) const {
const SanitizerArgs &SanArgs = getSanitizerArgs();
if (SanArgs.hasAnySanitizer())
  CC1Args.push_back("-D_REENTRANT");

}

[compnerd]

Sounds safe enough to me. I think that it would be nice to add a test that checks the hexagon flags as well.

[MaskRay]

Add hexagon test

lib/Driver/ToolChains/Clang.cpp

void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   // Only white-listed flags below are allowed to be embedded.
   if (C.getDriver().embedBitcodeInObject() && !C.getDriver().isUsingLTO() &&
       (isa<BackendJobAction>(JA) || isa<AssembleJobAction>(JA))) {
     // Add flags implied by -fembed-bitcode.
     Args.AddLastArg(CmdArgs, options::OPT_fembed_bitcode_EQ);
     // Disable all llvm IR level optimizations.
     CmdArgs.push_back("-disable-llvm-passes");
 
+    // Render target options such as -fuse-init-array on modern ELF platforms.
+    TC.addClangTargetOptions(Args, CmdArgs, JA.getOffloadingDeviceKind());
+
     // reject options that shouldn't be supported in bitcode
     // also reject kernel/kext
     static const constexpr unsigned kBitcodeOptionBlacklist[] = {
         options::OPT_mkernel,
         options::OPT_fapple_kext,
         options::OPT_ffunction_sections,
         options::OPT_fno_function_sections,
         options::OPT_fdata_sections,

test/Driver/fembed-bitcode.c

 
 // CHECK-AARCH64: "-cc1"
 
 // CHECK-AARCH64: "-cc1"
 // CHECK-AARCH64: "-target-abi"
 // CHECK-AARCH64: "darwinpcs"
 // CHECK-AARCH64-NOT: "-fdebug-compilation-dir"
 
+// RUN: %clang -target x86_64-pc-freebsd12 -fembed-bitcode=all -c %s -### 2>&1 \
+// RUN:     | FileCheck --check-prefix=CHECK-INITARRAY %s
+// CHECK-INITARRAY: "-fuse-init-array"
+
+// RUN: %clang -target hexagon-unknown-elf -ffixed-r19 -fembed-bitcode=all -c %s -### 2>&1 \
+// RUN:     | FileCheck --check-prefix=CHECK-HEXAGON %s
+// CHECK-HEXAGON: "-target-feature"
+// CHECK-HEXAGON: "+reserved-r19"