Author: Fangrui Song Date: 2021-01-09T00:32:01-08:00 New Revision: 1d3ebbf537832f80be97739abc4f6962caad1dab
URL: https://github.com/llvm/llvm-project/commit/1d3ebbf537832f80be97739abc4f6962caad1dab DIFF: https://github.com/llvm/llvm-project/commit/1d3ebbf537832f80be97739abc4f6962caad1dab.diff LOG: Add -f[no-]direct-access-external-data to supersede -mpie-copy-relocations GCC r218397 "x86-64: Optimize access to globals in PIE with copy reloc" made -fpie code emit R_X86_64_PC32 to reference external data symbols by default. Clang adopted -mpie-copy-relocations D19996 as a flexible alternative. The name -mpie-copy-relocations can be improved [1] and does not capture the idea that this option can apply to -fno-pic and -fpic [2], so this patch introduces -f[no-]direct-access-external-data and makes -mpie-copy-relocations their aliases for compatibility. [1] For ``` extern int var; int get() { return var; } ``` if var is defined in another translation unit in the link unit, there is no copy relocation. [2] -fno-pic -fno-direct-access-external-data is useful to avoid copy relocations. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65888 If a shared object is linked with -Bsymbolic or --dynamic-list and exports a data symbol, normally the data symbol cannot be accessed by -fno-pic code (because by default an absolute relocation is produced which will lead to a copy relocation). -fno-direct-access-external-data can prevent copy relocations. -fpic -fdirect-access-external-data can avoid GOT indirection. This is like the undefined counterpart of -fno-semantic-interposition. However, the user should define var in another translation unit and link with -Bsymbolic or --dynamic-list, otherwise the linker will error in a -shared link. Generally the user has better tools for their goal but I want to mention that this combination is valid. On COFF, the behavior is like always -fdirect-access-external-data. `__declspec(dllimport)` is needed to enable indirect access. There is currently no plan to affect non-ELF behaviors or -fpic behaviors. -fno-pic -fno-direct-access-external-data will be implemented in the subsequent patch. GCC feature request https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98112 Reviewed By: tmsriram Differential Revision: https://reviews.llvm.org/D92633 Added: clang/test/Driver/fdirect-access-external-data.c Modified: clang/include/clang/Basic/CodeGenOptions.def clang/include/clang/Driver/Options.td clang/lib/CodeGen/CodeGenModule.cpp clang/lib/Driver/ToolChains/Clang.cpp clang/lib/Frontend/CompilerInvocation.cpp clang/test/CodeGen/dso-local-executable.c Removed: ################################################################################ diff --git a/clang/include/clang/Basic/CodeGenOptions.def b/clang/include/clang/Basic/CodeGenOptions.def index d3851df23122..5c8af65326ed 100644 --- a/clang/include/clang/Basic/CodeGenOptions.def +++ b/clang/include/clang/Basic/CodeGenOptions.def @@ -368,8 +368,8 @@ VALUE_CODEGENOPT(EmitCheckPathComponentsToStrip, 32, 0) /// Whether to report the hotness of the code region for optimization remarks. CODEGENOPT(DiagnosticsWithHotness, 1, 0) -/// Whether copy relocations support is available when building as PIE. -CODEGENOPT(PIECopyRelocations, 1, 0) +/// Whether to use direct access relocations (instead of GOT) to reference external data symbols. +CODEGENOPT(DirectAccessExternalData, 1, 0) /// Whether we should use the undefined behaviour optimization for control flow /// paths that reach the end of a function without executing a required return. diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td index 9e1059cd14f0..741c28aa1f01 100644 --- a/clang/include/clang/Driver/Options.td +++ b/clang/include/clang/Driver/Options.td @@ -2184,6 +2184,10 @@ def fpic : Flag<["-"], "fpic">, Group<f_Group>; 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 fdirect_access_external_data : Flag<["-"], "fdirect-access-external-data">, Group<f_Group>, Flags<[CC1Option]>, + HelpText<"Don't use GOT indirection to reference external data symbols">; +def fno_direct_access_external_data : Flag<["-"], "fno-direct-access-external-data">, Group<f_Group>, Flags<[CC1Option]>, + HelpText<"Use GOT indirection to reference external data symbols">; defm plt : BoolFOption<"plt", "CodeGenOpts.NoPLT", DefaultsToFalse, ChangedBy<NegFlag, [], "Use GOT indirection instead of PLT to make external function calls (x86 only)">, @@ -3151,10 +3155,10 @@ def mstack_protector_guard_offset_EQ : Joined<["-"], "mstack-protector-guard-off HelpText<"Use the given offset for addressing the stack-protector guard">; def mstack_protector_guard_reg_EQ : Joined<["-"], "mstack-protector-guard-reg=">, Group<m_Group>, Flags<[CC1Option]>, HelpText<"Use the given reg for addressing the stack-protector guard">; -defm pie_copy_relocations : BoolOption<"pie-copy-relocations", - "CodeGenOpts.PIECopyRelocations", DefaultsToFalse, - ChangedBy<PosFlag, [CC1Option], "Use copy relocations support for PIE builds">, - ResetBy<NegFlag>, BothFlags<[]>, "m">, Group<m_Group>; +def mpie_copy_relocations : Flag<["-"], "mpie-copy-relocations">, + Alias<fdirect_access_external_data>, Group<m_Group>; +def mno_pie_copy_relocations : Flag<["-"], "mno-pie-copy-relocations">, + Alias<fno_direct_access_external_data>, Group<m_Group>; def mfentry : Flag<["-"], "mfentry">, HelpText<"Insert calls to fentry at function entry (x86/SystemZ only)">, Flags<[CC1Option]>, Group<m_Group>, MarshallingInfoFlag<"CodeGenOpts.CallFEntry">; diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp index cfc0f732748c..959f149667d9 100644 --- a/clang/lib/CodeGen/CodeGenModule.cpp +++ b/clang/lib/CodeGen/CodeGenModule.cpp @@ -986,7 +986,7 @@ static bool shouldAssumeDSOLocal(const CodeGenModule &CGM, // If we can use copy relocations we can assume it is local. if (auto *Var = dyn_cast<llvm::GlobalVariable>(GV)) if (!Var->isThreadLocal() && - (RM == llvm::Reloc::Static || CGOpts.PIECopyRelocations)) + (RM == llvm::Reloc::Static || CGOpts.DirectAccessExternalData)) return true; // If we can use a plt entry as the symbol address we can assume it diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp index d6453777200f..be4fe7f8eddd 100644 --- a/clang/lib/Driver/ToolChains/Clang.cpp +++ b/clang/lib/Driver/ToolChains/Clang.cpp @@ -4851,11 +4851,14 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA, CmdArgs.push_back("-mms-bitfields"); } - if (Args.hasFlag(options::OPT_mpie_copy_relocations, - options::OPT_mno_pie_copy_relocations, - false)) { - CmdArgs.push_back("-mpie-copy-relocations"); - } + // Non-PIC code defaults to -fdirect-access-external-data while PIC code + // defaults to -fno-direct-access-external-data. Pass the option if diff erent + // from the default. + if (Arg *A = Args.getLastArg(options::OPT_fdirect_access_external_data, + options::OPT_fno_direct_access_external_data)) + if (A->getOption().matches(options::OPT_fdirect_access_external_data) != + (PICLevel == 0)) + A->render(Args, CmdArgs); if (Args.hasFlag(options::OPT_fno_plt, options::OPT_fplt, false)) { CmdArgs.push_back("-fno-plt"); diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp index dd66bf5b4efc..90203637ccbc 100644 --- a/clang/lib/Frontend/CompilerInvocation.cpp +++ b/clang/lib/Frontend/CompilerInvocation.cpp @@ -942,6 +942,13 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK, } } + // PIC defaults to -fno-direct-access-external-data while non-PIC defaults to + // -fdirect-access-external-data. + Opts.DirectAccessExternalData = + Args.hasArg(OPT_fdirect_access_external_data) || + (!Args.hasArg(OPT_fno_direct_access_external_data) && + getLastArgIntValue(Args, OPT_pic_level, 0, Diags) == 0); + // If -fuse-ctor-homing is set and limited debug info is already on, then use // constructor homing. if (Args.getLastArg(OPT_fuse_ctor_homing)) diff --git a/clang/test/CodeGen/dso-local-executable.c b/clang/test/CodeGen/dso-local-executable.c index f4a886d4639b..5c5c6f59c09c 100644 --- a/clang/test/CodeGen/dso-local-executable.c +++ b/clang/test/CodeGen/dso-local-executable.c @@ -42,7 +42,7 @@ // PIE-DAG: define dso_local i32* @zed() // PIE-DAG: declare void @import_func() -// RUN: %clang_cc1 -triple x86_64 -emit-llvm -pic-level 1 -pic-is-pie -mpie-copy-relocations %s -o - | FileCheck --check-prefix=PIE-DIRECT %s +// RUN: %clang_cc1 -triple x86_64 -emit-llvm -pic-level 1 -pic-is-pie -fdirect-access-external-data %s -o - | FileCheck --check-prefix=PIE-DIRECT %s // PIE-DIRECT: @baz = dso_local global i32 42 // PIE-DIRECT-NEXT: @import_var = external dso_local global i32 // PIE-DIRECT-NEXT: @weak_bar = extern_weak global i32 @@ -64,7 +64,7 @@ // NOPLT-DAG: define dso_local i32* @zed() // NOPLT-DAG: declare void @import_func() -// RUN: %clang_cc1 -triple x86_64 -emit-llvm -fno-plt -pic-level 1 -pic-is-pie -mpie-copy-relocations %s -o - | FileCheck --check-prefix=PIE-DIRECT-NOPLT %s +// RUN: %clang_cc1 -triple x86_64 -emit-llvm -fno-plt -pic-level 1 -pic-is-pie -fdirect-access-external-data %s -o - | FileCheck --check-prefix=PIE-DIRECT-NOPLT %s // PIE-DIRECT-NOPLT: @baz = dso_local global i32 42 // PIE-DIRECT-NOPLT-NEXT: @import_var = external dso_local global i32 // PIE-DIRECT-NOPLT-NEXT: @weak_bar = extern_weak global i32 @@ -75,7 +75,7 @@ // PIE-DIRECT-NOPLT-DAG: define dso_local i32* @zed() // PIE-DIRECT-NOPLT-DAG: declare void @import_func() -// RUN: %clang_cc1 -triple x86_64 -emit-llvm -pic-is-pie -fno-plt %s -o - | FileCheck --check-prefix=PIE-NO-PLT %s +// RUN: %clang_cc1 -triple x86_64 -emit-llvm -pic-level 1 -pic-is-pie -fno-plt %s -o - | FileCheck --check-prefix=PIE-NO-PLT %s // RUN: %clang_cc1 -triple powerpc64le -emit-llvm -mrelocation-model static %s -o - | FileCheck --check-prefix=PIE-NO-PLT %s // PIE-NO-PLT: @baz = dso_local global i32 42 // PIE-NO-PLT-NEXT: @import_var = external global i32 diff --git a/clang/test/Driver/fdirect-access-external-data.c b/clang/test/Driver/fdirect-access-external-data.c new file mode 100644 index 000000000000..c3fc93064179 --- /dev/null +++ b/clang/test/Driver/fdirect-access-external-data.c @@ -0,0 +1,18 @@ +/// -fno-pic code defaults to -fdirect-access-external-data. +// RUN: %clang -### -c -target x86_64 %s 2>&1 | FileCheck %s --check-prefix=DEFAULT +// RUN: %clang -### -c -target x86_64 %s -fdirect-access-external-data 2>&1 | FileCheck %s --check-prefix=DEFAULT +// RUN: %clang -### -c -target x86_64 %s -fdirect-access-external-data -fno-direct-access-external-data 2>&1 | FileCheck %s --check-prefix=INDIRECT + +/// -fpie/-fpic code defaults to -fdirect-access-external-data. +// RUN: %clang -### -c -target x86_64 %s -fpie 2>&1 | FileCheck %s --check-prefix=DEFAULT +// RUN: %clang -### -c -target x86_64 %s -fpie -fno-direct-access-external-data -fdirect-access-external-data 2>&1 | FileCheck %s --check-prefix=DIRECT +// RUN: %clang -### -c -target aarch64 %s -fpic 2>&1 | FileCheck %s --check-prefix=DEFAULT +// RUN: %clang -### -c -target aarch64 %s -fpic -fdirect-access-external-data 2>&1 | FileCheck %s --check-prefix=DIRECT + +/// -m[no-]pie-copy-relocations are aliases for compatibility. +// RUN: %clang -### -c -target riscv64 %s -mno-pie-copy-relocations 2>&1 | FileCheck %s --check-prefix=INDIRECT +// RUN: %clang -### -c -target riscv64 %s -fpic -mpie-copy-relocations 2>&1 | FileCheck %s --check-prefix=DIRECT + +// DEFAULT-NOT: direct-access-external-data" +// DIRECT: "-fdirect-access-external-data" +// INDIRECT: "-fno-direct-access-external-data" _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits