[llvm] [llvm-objdump][RISCV] Display `@plt' symbols when disassembling .plt section (PR #147933)
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Thu Jul 10 03:22:46 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-binary-utilities
Author: Ming-Yi Lai (mylai-mtk)
<details>
<summary>Changes</summary>
This patch adds dummy symbols for PLT entries for RISC-V 32-bit and 64-bit targets so llvm-objdump can show the function symbol that corresponds to each PLT entry.
---
Full diff: https://github.com/llvm/llvm-project/pull/147933.diff
4 Files Affected:
- (modified) llvm/lib/Object/ELFObjectFile.cpp (+4)
- (modified) llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCTargetDesc.cpp (+42)
- (added) llvm/test/tools/llvm-objdump/ELF/RISCV/rv32-plt.test (+44)
- (added) llvm/test/tools/llvm-objdump/ELF/RISCV/rv64-plt.test (+44)
``````````diff
diff --git a/llvm/lib/Object/ELFObjectFile.cpp b/llvm/lib/Object/ELFObjectFile.cpp
index 0e13d32bbe522..5597d7db6426d 100644
--- a/llvm/lib/Object/ELFObjectFile.cpp
+++ b/llvm/lib/Object/ELFObjectFile.cpp
@@ -810,6 +810,10 @@ ELFObjectFileBase::getPltEntries(const MCSubtargetInfo &STI) const {
JumpSlotReloc = ELF::R_HEX_JMP_SLOT;
GlobDatReloc = ELF::R_HEX_GLOB_DAT;
break;
+ case Triple::riscv32:
+ case Triple::riscv64:
+ JumpSlotReloc = ELF::R_RISCV_JUMP_SLOT;
+ break;
default:
return {};
}
diff --git a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCTargetDesc.cpp b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCTargetDesc.cpp
index f66c2d5f99cb3..61ecfb278a7d3 100644
--- a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCTargetDesc.cpp
+++ b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCTargetDesc.cpp
@@ -30,6 +30,7 @@
#include "llvm/MC/TargetRegistry.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/MathExtras.h"
#include <bitset>
#define GET_INSTRINFO_MC_DESC
@@ -305,6 +306,47 @@ class RISCVMCInstrAnalysis : public MCInstrAnalysis {
}
}
+ /// Returns (PLT virtual address, GOT virtual address) pairs for PLT entries.
+ std::vector<std::pair<uint64_t, uint64_t>>
+ findPltEntries(uint64_t PltSectionVA, ArrayRef<uint8_t> PltContents,
+ const MCSubtargetInfo &STI) const override {
+ uint32_t LoadInsnOpCode;
+ if (const Triple &T = STI.getTargetTriple(); T.isRISCV64())
+ LoadInsnOpCode = 0x3003; // ld
+ else if (T.isRISCV32())
+ LoadInsnOpCode = 0x2003; // lw
+ else
+ return {};
+
+ constexpr uint64_t FirstEntryAt = 32, EntrySize = 16;
+ if (PltContents.size() < FirstEntryAt + EntrySize)
+ return {};
+
+ std::vector<std::pair<uint64_t, uint64_t>> Results;
+ for (uint64_t EntryStart = FirstEntryAt,
+ EntryStartEnd = PltContents.size() - EntrySize;
+ EntryStart <= EntryStartEnd; EntryStart += EntrySize) {
+ const uint32_t AuipcInsn =
+ support::endian::read32le(PltContents.data() + EntryStart);
+ const bool IsAuipc = (AuipcInsn & 0x7F) == 0x17;
+ if (!IsAuipc)
+ continue;
+
+ const uint32_t LoadInsn =
+ support::endian::read32le(PltContents.data() + EntryStart + 4);
+ const bool IsLoad = (LoadInsn & 0x707F) == LoadInsnOpCode;
+ if (!IsLoad)
+ continue;
+
+ const uint64_t GotPltSlotVA = PltSectionVA + EntryStart +
+ (AuipcInsn & 0xFFFFF000) +
+ SignExtend64<12>(LoadInsn >> 20);
+ Results.emplace_back(PltSectionVA + EntryStart, GotPltSlotVA);
+ }
+
+ return Results;
+ }
+
private:
static bool maybeReturnAddress(MCRegister Reg) {
// X1 is used for normal returns, X5 for returns from outlined functions.
diff --git a/llvm/test/tools/llvm-objdump/ELF/RISCV/rv32-plt.test b/llvm/test/tools/llvm-objdump/ELF/RISCV/rv32-plt.test
new file mode 100644
index 0000000000000..2160dc77fdc09
--- /dev/null
+++ b/llvm/test/tools/llvm-objdump/ELF/RISCV/rv32-plt.test
@@ -0,0 +1,44 @@
+# RUN: yaml2obj %s | llvm-objdump -d --no-show-raw-insn - | FileCheck %s
+
+# CHECK: 00001470 <strcmp at plt>:
+# CHECK-NEXT: 1470: auipc t3, 0x2
+# CHECK-NEXT: 1474: lw t3, 0xfc(t3)
+# CHECK-NEXT: 1478: jalr t1, t3
+# CHECK-NEXT: 147c: nop
+
+--- !ELF
+FileHeader:
+ Class: ELFCLASS32
+ Data: ELFDATA2LSB
+ Type: ET_DYN
+ Machine: EM_RISCV
+ Flags: [ EF_RISCV_RVC, EF_RISCV_FLOAT_ABI_DOUBLE ]
+Sections:
+ - Name: .rela.plt
+ Type: SHT_RELA
+ Flags: [ SHF_ALLOC, SHF_INFO_LINK ]
+ Address: 0x290
+ Link: .dynsym
+ AddressAlign: 0x4
+ Info: .got.plt
+ Relocations:
+ - Offset: 0x356C
+ Symbol: strcmp
+ Type: R_RISCV_JUMP_SLOT
+ - Name: .plt
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC, SHF_EXECINSTR ]
+ Address: 0x1450
+ AddressAlign: 0x10
+ Content: 972300003303C34103AE4311130343FD938243111353230083A2420067000E00172E0000032ECE0F67030E0013000000
+ - Name: .got.plt
+ Type: SHT_PROGBITS
+ Flags: [ SHF_WRITE, SHF_ALLOC ]
+ Address: 0x3564
+ AddressAlign: 0x4
+ Content: '000000000000000050140000'
+DynamicSymbols:
+ - Name: strcmp
+ Type: STT_FUNC
+ Binding: STB_GLOBAL
+...
diff --git a/llvm/test/tools/llvm-objdump/ELF/RISCV/rv64-plt.test b/llvm/test/tools/llvm-objdump/ELF/RISCV/rv64-plt.test
new file mode 100644
index 0000000000000..a6ecbf4a0a33f
--- /dev/null
+++ b/llvm/test/tools/llvm-objdump/ELF/RISCV/rv64-plt.test
@@ -0,0 +1,44 @@
+# RUN: yaml2obj %s | llvm-objdump -d --no-show-raw-insn - | FileCheck %s
+
+# CHECK: 0000000000001630 <strcmp at plt>:
+# CHECK-NEXT: 1630: auipc t3, 0x2
+# CHECK-NEXT: 1634: ld t3, 0x1b8(t3)
+# CHECK-NEXT: 1638: jalr t1, t3
+# CHECK-NEXT: 163c: nop
+
+--- !ELF
+FileHeader:
+ Class: ELFCLASS64
+ Data: ELFDATA2LSB
+ Type: ET_DYN
+ Machine: EM_RISCV
+ Flags: [ EF_RISCV_RVC, EF_RISCV_FLOAT_ABI_DOUBLE ]
+Sections:
+ - Name: .rela.plt
+ Type: SHT_RELA
+ Flags: [ SHF_ALLOC, SHF_INFO_LINK ]
+ Address: 0x408
+ Link: .dynsym
+ AddressAlign: 0x8
+ Info: .got.plt
+ Relocations:
+ - Offset: 0x37E8
+ Symbol: strcmp
+ Type: R_RISCV_JUMP_SLOT
+ - Name: .plt
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC, SHF_EXECINSTR ]
+ Address: 0x1610
+ AddressAlign: 0x10
+ Content: 972300003303C34103BE831C130343FD9382831C1353130083B2820067000E00172E0000033E8E1B67030E0013000000
+ - Name: .got.plt
+ Type: SHT_PROGBITS
+ Flags: [ SHF_WRITE, SHF_ALLOC ]
+ Address: 0x37D8
+ AddressAlign: 0x8
+ Content: '000000000000000000000000000000001016000000000000'
+DynamicSymbols:
+ - Name: strcmp
+ Type: STT_FUNC
+ Binding: STB_GLOBAL
+...
``````````
</details>
https://github.com/llvm/llvm-project/pull/147933
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