tmsriram created this revision. New clang option -fno-plt which avoids the PLT and lazy binding while making external calls.
GCC supports -fno-plt, https://gcc.gnu.org/ml/gcc-patches/2015-05/msg00001.html. This patch adds this to clang which marks all externally defined functions with the "nolazybind" attribute. This LLVM patch skips the PLT for calls to these functions, https://reviews.llvm.org/D39065. https://reviews.llvm.org/D39079 Files: include/clang/Driver/Options.td include/clang/Frontend/CodeGenOptions.def lib/CodeGen/CGCall.cpp lib/Driver/ToolChains/Clang.cpp lib/Frontend/CompilerInvocation.cpp Index: lib/Frontend/CompilerInvocation.cpp =================================================================== --- lib/Frontend/CompilerInvocation.cpp +++ lib/Frontend/CompilerInvocation.cpp @@ -650,6 +650,7 @@ Args.hasArg(OPT_mincremental_linker_compatible); Opts.PIECopyRelocations = Args.hasArg(OPT_mpie_copy_relocations); + Opts.NoPLT = Args.hasArg(OPT_fno_plt); Opts.OmitLeafFramePointer = Args.hasArg(OPT_momit_leaf_frame_pointer); Opts.SaveTempLabels = Args.hasArg(OPT_msave_temp_labels); Opts.NoDwarfDirectoryAsm = Args.hasArg(OPT_fno_dwarf_directory_asm); Index: lib/Driver/ToolChains/Clang.cpp =================================================================== --- lib/Driver/ToolChains/Clang.cpp +++ lib/Driver/ToolChains/Clang.cpp @@ -3386,6 +3386,10 @@ CmdArgs.push_back("-mpie-copy-relocations"); } + if (Args.hasFlag(options::OPT_fno_plt, options::OPT_fplt, false)) { + CmdArgs.push_back("-fno-plt"); + } + // -fhosted is default. // TODO: Audit uses of KernelOrKext and see where it'd be more appropriate to // use Freestanding. Index: lib/CodeGen/CGCall.cpp =================================================================== --- lib/CodeGen/CGCall.cpp +++ lib/CodeGen/CGCall.cpp @@ -1852,6 +1852,16 @@ !(TargetDecl && TargetDecl->hasAttr<NoSplitStackAttr>())) FuncAttrs.addAttribute("split-stack"); + // Add NonLazyBind attribute to function declarations when -fno-plt + // is used. + if (TargetDecl && CodeGenOpts.NoPLT) { + if (auto *Fn = dyn_cast<FunctionDecl>(TargetDecl)) { + if (!Fn->isDefined() && !AttrOnCallSite) { + FuncAttrs.addAttribute(llvm::Attribute::NonLazyBind); + } + } + } + if (!AttrOnCallSite) { bool DisableTailCalls = CodeGenOpts.DisableTailCalls || Index: include/clang/Frontend/CodeGenOptions.def =================================================================== --- include/clang/Frontend/CodeGenOptions.def +++ include/clang/Frontend/CodeGenOptions.def @@ -294,6 +294,8 @@ /// Whether to emit .debug_gnu_pubnames section instead of .debug_pubnames. CODEGENOPT(GnuPubnames, 1, 0) +CODEGENOPT(NoPLT, 1, 0) + #undef CODEGENOPT #undef ENUM_CODEGENOPT #undef VALUE_CODEGENOPT Index: include/clang/Driver/Options.td =================================================================== --- include/clang/Driver/Options.td +++ include/clang/Driver/Options.td @@ -1363,6 +1363,10 @@ def fno_pic : Flag<["-"], "fno-pic">, Group<f_Group>; def fpie : Flag<["-"], "fpie">, Group<f_Group>; def fno_pie : Flag<["-"], "fno-pie">, Group<f_Group>; +def fplt : Flag<["-"], "fplt">, Group<f_Group>, Flags<[CC1Option]>, + HelpText<"Use the PLT to make function calls">; +def fno_plt : Flag<["-"], "fno-plt">, Group<f_Group>, Flags<[CC1Option]>, + HelpText<"Do not use the PLT to make function calls">; def fropi : Flag<["-"], "fropi">, Group<f_Group>; def fno_ropi : Flag<["-"], "fno-ropi">, Group<f_Group>; def frwpi : Flag<["-"], "frwpi">, Group<f_Group>;
Index: lib/Frontend/CompilerInvocation.cpp =================================================================== --- lib/Frontend/CompilerInvocation.cpp +++ lib/Frontend/CompilerInvocation.cpp @@ -650,6 +650,7 @@ Args.hasArg(OPT_mincremental_linker_compatible); Opts.PIECopyRelocations = Args.hasArg(OPT_mpie_copy_relocations); + Opts.NoPLT = Args.hasArg(OPT_fno_plt); Opts.OmitLeafFramePointer = Args.hasArg(OPT_momit_leaf_frame_pointer); Opts.SaveTempLabels = Args.hasArg(OPT_msave_temp_labels); Opts.NoDwarfDirectoryAsm = Args.hasArg(OPT_fno_dwarf_directory_asm); Index: lib/Driver/ToolChains/Clang.cpp =================================================================== --- lib/Driver/ToolChains/Clang.cpp +++ lib/Driver/ToolChains/Clang.cpp @@ -3386,6 +3386,10 @@ CmdArgs.push_back("-mpie-copy-relocations"); } + if (Args.hasFlag(options::OPT_fno_plt, options::OPT_fplt, false)) { + CmdArgs.push_back("-fno-plt"); + } + // -fhosted is default. // TODO: Audit uses of KernelOrKext and see where it'd be more appropriate to // use Freestanding. Index: lib/CodeGen/CGCall.cpp =================================================================== --- lib/CodeGen/CGCall.cpp +++ lib/CodeGen/CGCall.cpp @@ -1852,6 +1852,16 @@ !(TargetDecl && TargetDecl->hasAttr<NoSplitStackAttr>())) FuncAttrs.addAttribute("split-stack"); + // Add NonLazyBind attribute to function declarations when -fno-plt + // is used. + if (TargetDecl && CodeGenOpts.NoPLT) { + if (auto *Fn = dyn_cast<FunctionDecl>(TargetDecl)) { + if (!Fn->isDefined() && !AttrOnCallSite) { + FuncAttrs.addAttribute(llvm::Attribute::NonLazyBind); + } + } + } + if (!AttrOnCallSite) { bool DisableTailCalls = CodeGenOpts.DisableTailCalls || Index: include/clang/Frontend/CodeGenOptions.def =================================================================== --- include/clang/Frontend/CodeGenOptions.def +++ include/clang/Frontend/CodeGenOptions.def @@ -294,6 +294,8 @@ /// Whether to emit .debug_gnu_pubnames section instead of .debug_pubnames. CODEGENOPT(GnuPubnames, 1, 0) +CODEGENOPT(NoPLT, 1, 0) + #undef CODEGENOPT #undef ENUM_CODEGENOPT #undef VALUE_CODEGENOPT Index: include/clang/Driver/Options.td =================================================================== --- include/clang/Driver/Options.td +++ include/clang/Driver/Options.td @@ -1363,6 +1363,10 @@ def fno_pic : Flag<["-"], "fno-pic">, Group<f_Group>; def fpie : Flag<["-"], "fpie">, Group<f_Group>; def fno_pie : Flag<["-"], "fno-pie">, Group<f_Group>; +def fplt : Flag<["-"], "fplt">, Group<f_Group>, Flags<[CC1Option]>, + HelpText<"Use the PLT to make function calls">; +def fno_plt : Flag<["-"], "fno-plt">, Group<f_Group>, Flags<[CC1Option]>, + HelpText<"Do not use the PLT to make function calls">; def fropi : Flag<["-"], "fropi">, Group<f_Group>; def fno_ropi : Flag<["-"], "fno-ropi">, Group<f_Group>; def frwpi : Flag<["-"], "frwpi">, Group<f_Group>;
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