https://github.com/phoebewang updated https://github.com/llvm/llvm-project/pull/206002
>From 0892425b2582788a8937655cfa739863034b978b Mon Sep 17 00:00:00 2001 From: Phoebe Wang <[email protected]> Date: Fri, 26 Jun 2026 15:45:06 +0800 Subject: [PATCH 1/3] [X86] Add dynamic section support per psABI Add option [no]mark-plt to enable it. Dynamic linker can change PLT entries with JMPABS instruction on supported targets. --- lld/ELF/Config.h | 1 + lld/ELF/Driver.cpp | 1 + lld/ELF/Relocations.cpp | 10 ++++- lld/ELF/SyntheticSections.cpp | 7 ++++ lld/test/ELF/x86-64-mark-plt.s | 37 +++++++++++++++++++ .../include/llvm/BinaryFormat/DynamicTags.def | 19 ++++++++++ llvm/lib/Object/ELF.cpp | 22 +++++++++++ 7 files changed, 96 insertions(+), 1 deletion(-) create mode 100644 lld/test/ELF/x86-64-mark-plt.s diff --git a/lld/ELF/Config.h b/lld/ELF/Config.h index 12b16ded61fca..d6590ab284e5b 100644 --- a/lld/ELF/Config.h +++ b/lld/ELF/Config.h @@ -439,6 +439,7 @@ struct Config { bool zKeepDataSectionPrefix; bool zKeepTextSectionPrefix; bool zLrodataAfterBss; + bool zMarkPlt; bool zNoBtCfi; bool zNodefaultlib; bool zNodelete; diff --git a/lld/ELF/Driver.cpp b/lld/ELF/Driver.cpp index 7ec7dfcae6bca..c41991e377832 100644 --- a/lld/ELF/Driver.cpp +++ b/lld/ELF/Driver.cpp @@ -1657,6 +1657,7 @@ static void readConfigs(Ctx &ctx, opt::InputArgList &args) { args, "keep-text-section-prefix", "nokeep-text-section-prefix", false); ctx.arg.zLrodataAfterBss = getZFlag(args, "lrodata-after-bss", "nolrodata-after-bss", false); + ctx.arg.zMarkPlt = getZFlag(args, "mark-plt", "nomark-plt", false); ctx.arg.zNoBtCfi = hasZOption(args, "nobtcfi"); ctx.arg.zNodefaultlib = hasZOption(args, "nodefaultlib"); ctx.arg.zNodelete = hasZOption(args, "nodelete"); diff --git a/lld/ELF/Relocations.cpp b/lld/ELF/Relocations.cpp index 0d45236e6d11e..b8aac5b5b63f4 100644 --- a/lld/ELF/Relocations.cpp +++ b/lld/ELF/Relocations.cpp @@ -749,9 +749,17 @@ static void addPltEntry(Ctx &ctx, PltSection &plt, GotPltSection &gotPlt, RelocationBaseSection &rel, RelType type, Symbol &sym) { plt.addEntry(sym); gotPlt.addEntry(sym); + // The x86-64 psABI requires the r_addend of R_X86_64_JUMP_SLOT to hold the + // link-time VA of the PLT entry so that the dynamic linker can locate the + // indirect branch (l->l_addr + r_addend) and rewrite it to a direct branch + // when -z mark-plt is active. + RelExpr addendExpr = R_ADDEND; + if (ctx.arg.emachine == EM_X86_64 && ctx.arg.zMarkPlt && + type == ctx.target->pltRel) + addendExpr = R_PLT; if (sym.isPreemptible) rel.addReloc( - {type, &gotPlt, sym.getGotPltOffset(ctx), true, sym, 0, R_ADDEND}); + {type, &gotPlt, sym.getGotPltOffset(ctx), true, sym, 0, addendExpr}); else rel.addReloc( {type, &gotPlt, sym.getGotPltOffset(ctx), false, sym, 0, R_ABS}); diff --git a/lld/ELF/SyntheticSections.cpp b/lld/ELF/SyntheticSections.cpp index b9a42590dc8e7..ac417e160f31d 100644 --- a/lld/ELF/SyntheticSections.cpp +++ b/lld/ELF/SyntheticSections.cpp @@ -1318,6 +1318,13 @@ DynamicSection<ELFT>::computeContents() { addInt(DT_PLTREL, ctx.arg.isRela ? DT_RELA : DT_REL); } + if (ctx.arg.emachine == EM_X86_64 && ctx.arg.zMarkPlt && + ctx.in.plt->isNeeded()) { + addInSec(DT_X86_64_PLT, *ctx.in.plt); + addInt(DT_X86_64_PLTSZ, ctx.in.plt->getSize()); + addInt(DT_X86_64_PLTENT, ctx.target->pltEntrySize); + } + if (ctx.arg.emachine == EM_AARCH64) { if (ctx.arg.andFeatures & GNU_PROPERTY_AARCH64_FEATURE_1_BTI) addInt(DT_AARCH64_BTI_PLT, 0); diff --git a/lld/test/ELF/x86-64-mark-plt.s b/lld/test/ELF/x86-64-mark-plt.s new file mode 100644 index 0000000000000..e177c64ee418f --- /dev/null +++ b/lld/test/ELF/x86-64-mark-plt.s @@ -0,0 +1,37 @@ +# REQUIRES: x86 +# RUN: llvm-mc -filetype=obj -triple=x86_64 %s -o %t.o +# RUN: llvm-mc -filetype=obj -triple=x86_64 %p/Inputs/shared.s -o %t2.o +# RUN: ld.lld -shared -soname=t2 %t2.o -o %t2.so + +## -z mark-plt emits DT_X86_64_PLT, DT_X86_64_PLTSZ, DT_X86_64_PLTENT. +## PLT layout: 16-byte header + 1 entry * 16 bytes = 0x20 bytes total. +# RUN: ld.lld %t.o %t2.so -z mark-plt -z now -o %t +# RUN: llvm-readelf --dynamic-table %t | FileCheck %s --check-prefix=MARK +# RUN: llvm-readelf --relocs %t | FileCheck %s --check-prefix=RELA + +## Without -z mark-plt: no tags and zero addend on JUMP_SLOT. +# RUN: ld.lld %t.o %t2.so -z now -o %t.nomark +# RUN: llvm-readelf --dynamic-table %t.nomark | FileCheck %s --check-prefix=NOMARK +# RUN: llvm-readelf --relocs %t.nomark | FileCheck %s --check-prefix=NORELA + +## -z mark-plt also works for shared libraries. +# RUN: ld.lld -shared %t.o %t2.so -z mark-plt -z now -o %t.so +# RUN: llvm-readelf --dynamic-table %t.so | FileCheck %s --check-prefix=MARK + +# MARK: 0x0000000070000000 (X86_64_PLT) {{0x[0-9a-f]+}} +# MARK: 0x0000000070000001 (X86_64_PLTSZ) 0x20 +# MARK: 0x0000000070000003 (X86_64_PLTENT) 0x10 + +# NOMARK-NOT: (X86_64_PLT) +# NOMARK-NOT: (X86_64_PLTSZ) +# NOMARK-NOT: (X86_64_PLTENT) + +## With -z mark-plt, R_X86_64_JUMP_SLOT addend is the PLT entry VA (non-zero). +# RELA: R_X86_64_JUMP_SLOT {{.*}} bar + {{[1-9a-f][0-9a-f]+}} + +## Without -z mark-plt, R_X86_64_JUMP_SLOT addend is 0. +# NORELA: R_X86_64_JUMP_SLOT {{.*}} bar + 0 + +.globl _start +_start: + call bar@plt diff --git a/llvm/include/llvm/BinaryFormat/DynamicTags.def b/llvm/include/llvm/BinaryFormat/DynamicTags.def index 1e9b87e1e58a7..c700044920575 100644 --- a/llvm/include/llvm/BinaryFormat/DynamicTags.def +++ b/llvm/include/llvm/BinaryFormat/DynamicTags.def @@ -41,6 +41,11 @@ #define SPARC_DYNAMIC_TAG_DEFINED #endif +#ifndef X86_64_DYNAMIC_TAG +#define X86_64_DYNAMIC_TAG(name, value) DYNAMIC_TAG(name, value) +#define X86_64_DYNAMIC_TAG_DEFINED +#endif + #ifndef DYNAMIC_TAG_MARKER #define DYNAMIC_TAG_MARKER(name, value) DYNAMIC_TAG(name, value) #define DYNAMIC_TAG_MARKER_DEFINED @@ -248,6 +253,12 @@ RISCV_DYNAMIC_TAG(RISCV_VARIANT_CC, 0x70000001) SPARC_DYNAMIC_TAG(SPARC_REGISTER, 0x70000001) +// x86-64 specific dynamic table entry tags. + +X86_64_DYNAMIC_TAG(X86_64_PLT, 0x70000000) // Address of PLT table. +X86_64_DYNAMIC_TAG(X86_64_PLTSZ, 0x70000001) // Size of PLT table in bytes. +X86_64_DYNAMIC_TAG(X86_64_PLTENT, 0x70000003) // Size of a PLT entry in bytes. + // Sun machine-independent extensions. DYNAMIC_TAG(AUXILIARY, 0x7FFFFFFD) // Shared object to load before self DYNAMIC_TAG(USED, 0x7FFFFFFE) // Same as DT_NEEDED @@ -282,3 +293,11 @@ DYNAMIC_TAG(FILTER, 0x7FFFFFFF) // Shared object to get values from #undef RISCV_DYNAMIC_TAG #undef RISCV_DYNAMIC_TAG_DEFINED #endif +#ifdef SPARC_DYNAMIC_TAG_DEFINED +#undef SPARC_DYNAMIC_TAG +#undef SPARC_DYNAMIC_TAG_DEFINED +#endif +#ifdef X86_64_DYNAMIC_TAG_DEFINED +#undef X86_64_DYNAMIC_TAG +#undef X86_64_DYNAMIC_TAG_DEFINED +#endif diff --git a/llvm/lib/Object/ELF.cpp b/llvm/lib/Object/ELF.cpp index f159fd82e7117..48dd225932ba8 100644 --- a/llvm/lib/Object/ELF.cpp +++ b/llvm/lib/Object/ELF.cpp @@ -588,6 +588,24 @@ std::string ELFFile<ELFT>::getDynamicTagAsString(unsigned Arch, #undef RISCV_DYNAMIC_TAG } break; + + case ELF::EM_SPARC: + case ELF::EM_SPARC32PLUS: + case ELF::EM_SPARCV9: + switch (Type) { +#define SPARC_DYNAMIC_TAG(name, value) DYNAMIC_STRINGIFY_ENUM(name, value) +#include "llvm/BinaryFormat/DynamicTags.def" +#undef SPARC_DYNAMIC_TAG + } + break; + + case ELF::EM_X86_64: + switch (Type) { +#define X86_64_DYNAMIC_TAG(name, value) DYNAMIC_STRINGIFY_ENUM(name, value) +#include "llvm/BinaryFormat/DynamicTags.def" +#undef X86_64_DYNAMIC_TAG + } + break; } #undef DYNAMIC_TAG switch (Type) { @@ -598,6 +616,8 @@ std::string ELFFile<ELFT>::getDynamicTagAsString(unsigned Arch, #define PPC_DYNAMIC_TAG(name, value) #define PPC64_DYNAMIC_TAG(name, value) #define RISCV_DYNAMIC_TAG(name, value) +#define SPARC_DYNAMIC_TAG(name, value) +#define X86_64_DYNAMIC_TAG(name, value) // Also ignore marker tags such as DT_HIOS (maps to DT_VERNEEDNUM), etc. #define DYNAMIC_TAG_MARKER(name, value) #define DYNAMIC_TAG(name, value) case value: return #name; @@ -609,6 +629,8 @@ std::string ELFFile<ELFT>::getDynamicTagAsString(unsigned Arch, #undef PPC_DYNAMIC_TAG #undef PPC64_DYNAMIC_TAG #undef RISCV_DYNAMIC_TAG +#undef SPARC_DYNAMIC_TAG +#undef X86_64_DYNAMIC_TAG #undef DYNAMIC_TAG_MARKER #undef DYNAMIC_STRINGIFY_ENUM default: >From d16048a10dbca3492448bff3052734ae2f9bfe1e Mon Sep 17 00:00:00 2001 From: Phoebe Wang <[email protected]> Date: Fri, 26 Jun 2026 16:35:01 +0800 Subject: [PATCH 2/3] Fix lldb failure --- .../Plugins/ObjectFile/ELF/ObjectFileELF.cpp | 22 +++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp b/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp index 16dd2fc122906..f343939ad115f 100644 --- a/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp +++ b/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp @@ -3800,6 +3800,24 @@ std::string static getDynamicTagAsString(uint16_t Arch, uint64_t Type) { #undef RISCV_DYNAMIC_TAG } break; + + case llvm::ELF::EM_SPARC: + case llvm::ELF::EM_SPARC32PLUS: + case llvm::ELF::EM_SPARCV9: + switch (Type) { +#define SPARC_DYNAMIC_TAG(name, value) DYNAMIC_STRINGIFY_ENUM(name, value) +#include "llvm/BinaryFormat/DynamicTags.def" +#undef SPARC_DYNAMIC_TAG + } + break; + + case llvm::ELF::EM_X86_64: + switch (Type) { +#define X86_64_DYNAMIC_TAG(name, value) DYNAMIC_STRINGIFY_ENUM(name, value) +#include "llvm/BinaryFormat/DynamicTags.def" +#undef X86_64_DYNAMIC_TAG + } + break; } #undef DYNAMIC_TAG switch (Type) { @@ -3810,6 +3828,8 @@ std::string static getDynamicTagAsString(uint16_t Arch, uint64_t Type) { #define PPC_DYNAMIC_TAG(name, value) #define PPC64_DYNAMIC_TAG(name, value) #define RISCV_DYNAMIC_TAG(name, value) +#define SPARC_DYNAMIC_TAG(name, value) +#define X86_64_DYNAMIC_TAG(name, value) // Also ignore marker tags such as DT_HIOS (maps to DT_VERNEEDNUM), etc. #define DYNAMIC_TAG_MARKER(name, value) #define DYNAMIC_TAG(name, value) \ @@ -3823,6 +3843,8 @@ std::string static getDynamicTagAsString(uint16_t Arch, uint64_t Type) { #undef PPC_DYNAMIC_TAG #undef PPC64_DYNAMIC_TAG #undef RISCV_DYNAMIC_TAG +#undef SPARC_DYNAMIC_TAG +#undef X86_64_DYNAMIC_TAG #undef DYNAMIC_TAG_MARKER #undef DYNAMIC_STRINGIFY_ENUM default: >From 832a36f14668dfcb24659f26c5d630e2a5796eef Mon Sep 17 00:00:00 2001 From: Phoebe Wang <[email protected]> Date: Sat, 27 Jun 2026 21:00:28 +0800 Subject: [PATCH 3/3] Add llvm-readelf and llvm-objdump testing --- .../ELF/dynamic-tags-machine-specific.test | 46 +++++++++++++++++++ 1 file changed, 46 insertions(+) diff --git a/llvm/test/tools/llvm-readobj/ELF/dynamic-tags-machine-specific.test b/llvm/test/tools/llvm-readobj/ELF/dynamic-tags-machine-specific.test index 9a338a852ffe7..fcc365e528dea 100644 --- a/llvm/test/tools/llvm-readobj/ELF/dynamic-tags-machine-specific.test +++ b/llvm/test/tools/llvm-readobj/ELF/dynamic-tags-machine-specific.test @@ -483,3 +483,49 @@ ProgramHeaders: - Type: PT_DYNAMIC FirstSec: .dynamic LastSec: .dynamic + +## Case 8: Test that x86-64 machine-specific tags can be dumped. +# RUN: yaml2obj --docnum=8 %s -o %t.x86_64 +# RUN: llvm-readobj --dynamic-table %t.x86_64 | FileCheck %s --check-prefix=LLVM-X86_64 +# RUN: llvm-readelf --dynamic-table %t.x86_64 | FileCheck %s --check-prefix=GNU-X86_64 + +# LLVM-X86_64: DynamicSection [ (4 entries) +# LLVM-X86_64-NEXT: Tag Type Name/Value +# LLVM-X86_64-NEXT: 0x0000000070000000 X86_64_PLT 0x401020 +# LLVM-X86_64-NEXT: 0x0000000070000001 X86_64_PLTSZ 0x20 +# LLVM-X86_64-NEXT: 0x0000000070000003 X86_64_PLTENT 0x10 +# LLVM-X86_64-NEXT: 0x0000000000000000 NULL 0x0 +# LLVM-X86_64-NEXT: ] + +# GNU-X86_64: Dynamic section at offset {{.*}} contains 4 entries: +# GNU-X86_64-NEXT: Tag Type Name/Value +# GNU-X86_64-NEXT: 0x0000000070000000 (X86_64_PLT) 0x401020 +# GNU-X86_64-NEXT: 0x0000000070000001 (X86_64_PLTSZ) 0x20 +# GNU-X86_64-NEXT: 0x0000000070000003 (X86_64_PLTENT) 0x10 +# GNU-X86_64-NEXT: 0x0000000000000000 (NULL) 0x0 + +--- !ELF +FileHeader: + Class: ELFCLASS64 + Data: ELFDATA2LSB + Type: ET_EXEC + Machine: EM_X86_64 +Sections: + - Name: .dynamic + Type: SHT_DYNAMIC + Entries: + - Tag: DT_X86_64_PLT + Value: 0x401020 + - Tag: DT_X86_64_PLTSZ + Value: 0x20 + - Tag: DT_X86_64_PLTENT + Value: 0x10 + - Tag: DT_NULL + Value: 0 +ProgramHeaders: + - Type: PT_LOAD + FirstSec: .dynamic + LastSec: .dynamic + - Type: PT_DYNAMIC + FirstSec: .dynamic + LastSec: .dynamic _______________________________________________ lldb-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-commits
