[PowerPC] Option for secure plt mode

[spetrovic]

Summary

This patch enables option for secure plt mode in clang (-msecure-plt). This feature is supported in backend also (https://reviews.llvm.org/D42112).

[nemanjai]

I'll let Justin give the actual ACK, but this looks fine to me. The only question that I have (since I don't know anything about secure PLT) is whether this is a PPC-specific thing (since the option is a PPC option).

include/clang/Driver/Options.td

1941 ↗

(On Diff #139904)

Do we not want the negated option?

lib/Driver/ToolChains/Arch/PPC.cpp

116 ↗

(On Diff #139904)

Just a style question out of curiosity. Why the temporary? Since there are just two possible values, why not just return the respective enumerator?

[spetrovic]

include/clang/Driver/Options.td

1941 ↗

(On Diff #139904)

Well, I'm not sure if we need negated option. This is just switch from default mode (BSS) to SECURE PLT mode, also I didn't see that gcc has negated option for SECURE-PLT.

lib/Driver/ToolChains/Arch/PPC.cpp

116 ↗

(On Diff #139904)

You are right, we don't need the temporary.

[spetrovic]

Yes, secure PLT is PowerPC specific feature.

[joerg]

GCC supports -mbss-plt to get the legacy behavior. Not sure if anyone actually uses it though.

[nemanjai]

In D44921#1050299, @joerg wrote:

GCC supports -mbss-plt to get the legacy behavior. Not sure if anyone actually uses it though.

@spetrovic Is this something we want to implement?

[spetrovic]

-mbss-plt is currently default in LLVM, once secure plt support is finished we can set secure plt as default in LLVM, but not for now.

[nemanjai]

In D44921#1056672, @spetrovic wrote:

-mbss-plt is currently default in LLVM, once secure plt support is finished we can set secure plt as default in LLVM, but not for now.

I was thinking in case the override is needed to override something specified in make files, etc. of some build systems. In any case, this all looks fine to me. Perhaps @jhibbits/@chmeee or @joerg should give the final ACK for this. If not, I'll approve it next time you ping the patch.

cfe/trunk/include/clang/Driver/Options.td

def mno_xnack : Flag<["-"], "mno-xnack">, Group<m_amdgpu_Features_Group>,
   HelpText<"Disable XNACK (AMDGPU only)">;
 
 def faltivec : Flag<["-"], "faltivec">, Group<f_Group>, Flags<[DriverOption]>;
 def fno_altivec : Flag<["-"], "fno-altivec">, Group<f_Group>, Flags<[DriverOption]>;
 def maltivec : Flag<["-"], "maltivec">, Group<m_ppc_Features_Group>;
 def mno_altivec : Flag<["-"], "mno-altivec">, Group<m_ppc_Features_Group>;
 def mvsx : Flag<["-"], "mvsx">, Group<m_ppc_Features_Group>;
 def mno_vsx : Flag<["-"], "mno-vsx">, Group<m_ppc_Features_Group>;
+def msecure_plt : Flag<["-"], "msecure-plt">, Group<m_ppc_Features_Group>;
 def mpower8_vector : Flag<["-"], "mpower8-vector">,
     Group<m_ppc_Features_Group>;
 def mno_power8_vector : Flag<["-"], "mno-power8-vector">,
     Group<m_ppc_Features_Group>;
 def mpower9_vector : Flag<["-"], "mpower9-vector">,
     Group<m_ppc_Features_Group>;
 def mno_power9_vector : Flag<["-"], "mno-power9-vector">,
     Group<m_ppc_Features_Group>;

cfe/trunk/lib/Driver/ToolChains/Arch/PPC.h

 bool hasPPCAbiArg(const llvm::opt::ArgList &Args, const char *Value);
 
 enum class FloatABI {
   Invalid,
   Soft,
   Hard,
 };
 
+enum class ReadGOTPtrMode {
+  Bss,
+  SecurePlt,
+};
+
 FloatABI getPPCFloatABI(const Driver &D, const llvm::opt::ArgList &Args);
 
 std::string getPPCTargetCPU(const llvm::opt::ArgList &Args);
 const char *getPPCAsmModeForCPU(StringRef Name);
+ReadGOTPtrMode getPPCReadGOTPtrMode(const Driver &D,
+                                  const llvm::opt::ArgList &Args);
 
 void getPPCTargetFeatures(const Driver &D, const llvm::Triple &Triple,
                           const llvm::opt::ArgList &Args,
                           std::vector<llvm::StringRef> &Features);
 
 } // end namespace ppc
 } // end namespace target
 } // end namespace driver
 } // end namespace clang
 
 #endif // LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_ARCH_PPC_H

cfe/trunk/lib/Driver/ToolChains/Arch/PPC.cpp

 void ppc::getPPCTargetFeatures(const Driver &D, const llvm::Triple &Triple,
                                const ArgList &Args,
                                std::vector<StringRef> &Features) {
   handleTargetFeaturesGroup(Args, Features, options::OPT_m_ppc_Features_Group);
 
   ppc::FloatABI FloatABI = ppc::getPPCFloatABI(D, Args);
   if (FloatABI == ppc::FloatABI::Soft)
     Features.push_back("-hard-float");
+
+  ppc::ReadGOTPtrMode ReadGOT = ppc::getPPCReadGOTPtrMode(D, Args);
+  if (ReadGOT == ppc::ReadGOTPtrMode::SecurePlt)
+    Features.push_back("+secure-plt");
+}
+
+ppc::ReadGOTPtrMode ppc::getPPCReadGOTPtrMode(const Driver &D, const ArgList &Args) {
+  if (Args.getLastArg(options::OPT_msecure_plt))
+    return ppc::ReadGOTPtrMode::SecurePlt;
+  return ppc::ReadGOTPtrMode::Bss;
 }
 
 ppc::FloatABI ppc::getPPCFloatABI(const Driver &D, const ArgList &Args) {
   ppc::FloatABI ABI = ppc::FloatABI::Invalid;
   if (Arg *A =
           Args.getLastArg(options::OPT_msoft_float, options::OPT_mhard_float,
                           options::OPT_mfloat_abi_EQ)) {
     if (A->getOption().matches(options::OPT_msoft_float))

cfe/trunk/test/Driver/ppc-features.cpp

 // check combine -mhard-float -msoft-float option for ppc32
 // RUN: %clang -target powerpc-unknown-linux-gnu %s -mhard-float -msoft-float -### -o %t.o 2>&1 | FileCheck --check-prefix=CHECK-HARDSOFT %s
 // CHECK-HARDSOFT: "-target-feature" "-hard-float"
 
 // check combine -msoft-float -mhard-float option for ppc32
 // RUN: %clang -target powerpc-unknown-linux-gnu %s -msoft-float -mhard-float -### -o %t.o 2>&1 | FileCheck --check-prefix=CHECK-SOFTHARD %s
 // CHECK-SOFTHARD-NOT: "-target-feature" "-hard-float"
 
+// check -msecure-plt option for ppc32
+// RUN: %clang -target powerpc-unknown-linux-gnu -msecure-plt %s  -### -o %t.o 2>&1 | FileCheck --check-prefix=CHECK-SECUREPLT %s
+// CHECK-SECUREPLT: "-target-feature" "+secure-plt"
+
 // check -mfloat-abi=x option
 // RUN: %clang -target powerpc-unknown-linux-gnu %s -mfloat-abi=x -### -o %t.o 2>&1 | FileCheck --check-prefix=CHECK-ERRMSG %s
 // CHECK-ERRMSG: error: invalid float ABI '-mfloat-abi=x'
 
 // check -msoft-float option for ppc64
 // RUN: %clang -target powerpc64-unknown-linux-gnu %s -msoft-float -### -o %t.o 2>&1 | FileCheck --check-prefix=CHECK-SOFTFLOAT64 %s
 // CHECK-SOFTFLOAT64: "-target-feature" "-hard-float"