[llvm-nm] Introduce synthetic flag #138232
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@llvm/pr-subscribers-llvm-binary-utilities Author: Vladislav Khmelevsky (yota9) ChangesCompatible with GNU nm --syntethic option is used to show special Full diff: https://github.com/llvm/llvm-project/pull/138232.diff 3 Files Affected:
diff --git a/llvm/test/tools/llvm-nm/AArch64/synthetic.test b/llvm/test/tools/llvm-nm/AArch64/synthetic.test
new file mode 100644
index 0000000000000..c98770db6ab8a
--- /dev/null
+++ b/llvm/test/tools/llvm-nm/AArch64/synthetic.test
@@ -0,0 +1,90 @@
+## Test --synthetic flag.
+
+# RUN: yaml2obj %s -o %t
+
+# RUN: llvm-nm %t | count 0
+# RUN: llvm-nm %t --synthetic | FileCheck %s
+
+--- !ELF
+FileHeader:
+ Class: ELFCLASS64
+ Data: ELFDATA2LSB
+ Type: ET_DYN
+ Machine: EM_AARCH64
+Sections:
+ - Name: .rela.plt
+ Type: SHT_RELA
+ Flags: [ SHF_ALLOC, SHF_INFO_LINK ]
+ Address: 0x540
+ Link: .dynsym
+ AddressAlign: 0x8
+ Info: .got
+ Relocations:
+ - Offset: 0x10FA8
+ Symbol: __libc_start_main
+ Type: R_AARCH64_JUMP_SLOT
+ - Offset: 0x10FB0
+ Symbol: __cxa_finalize
+ Type: R_AARCH64_JUMP_SLOT
+ - Offset: 0x10FB8
+ Symbol: __gmon_start__
+ Type: R_AARCH64_JUMP_SLOT
+ - Offset: 0x10FC0
+ Symbol: abort
+ Type: R_AARCH64_JUMP_SLOT
+ - Offset: 0x10FC8
+ Symbol: puts
+ Type: R_AARCH64_JUMP_SLOT
+ - Name: .plt
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC, SHF_EXECINSTR ]
+ Address: 0x5D0
+ AddressAlign: 0x10
+ Content: F07BBFA99000009011D247F910823E9120021FD61F2003D51F2003D51F2003D59000009011D647F910A23E9120021FD69000009011DA47F910C23E9120021FD69000009011DE47F910E23E9120021FD69000009011E247F910023F9120021FD69000009011E647F910223F9120021FD6
+ - Name: .text
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC, SHF_EXECINSTR ]
+ Address: 0x640
+ - Name: .dynamic
+ Type: SHT_DYNAMIC
+ Flags: [ SHF_WRITE, SHF_ALLOC ]
+ Address: 0x10DA0
+ Link: .dynstr
+ AddressAlign: 0x8
+ Entries:
+ - Tag: DT_JMPREL
+ Value: 0x540
+ - Tag: DT_PLTRELSZ
+ Value: 0x78
+ - Tag: DT_PLTGOT
+ Value: 0x10F90
+ - Tag: DT_NULL
+ Value: 0x0
+ - Name: .got
+ Type: SHT_PROGBITS
+ Flags: [ SHF_WRITE, SHF_ALLOC ]
+ Address: 0x10F90
+ AddressAlign: 0x8
+ EntSize: 0x8
+ Content: 000000000000000000000000000000000000000000000000D005000000000000D005000000000000D005000000000000D005000000000000D005000000000000A00D01000000000000000000000000000000000000000000000000000000000054070000000000000000000000000000
+DynamicSymbols:
+ - Name: __libc_start_main
+ Type: STT_FUNC
+ Binding: STB_GLOBAL
+ - Name: __cxa_finalize
+ Type: STT_FUNC
+ Binding: STB_WEAK
+ - Name: __gmon_start__
+ Binding: STB_WEAK
+ - Name: abort
+ Type: STT_FUNC
+ Binding: STB_GLOBAL
+ - Name: puts
+ Type: STT_FUNC
+ Binding: STB_GLOBAL
+
+# CHECK: 0000000000000600 T __cxa_finalize@plt
+# CHECK-NEXT: 0000000000000610 T __gmon_start__@plt
+# CHECK-NEXT: 00000000000005f0 T __libc_start_main@plt
+# CHECK-NEXT: 0000000000000620 T abort@plt
+# CHECK-NEXT: 0000000000000630 T puts@plt
diff --git a/llvm/tools/llvm-nm/Opts.td b/llvm/tools/llvm-nm/Opts.td
index 04d9f5db5cf85..b534c3a26a8f8 100644
--- a/llvm/tools/llvm-nm/Opts.td
+++ b/llvm/tools/llvm-nm/Opts.td
@@ -35,6 +35,7 @@ defm radix : Eq<"radix", "Radix (o/d/x) for printing symbol Values">, MetaVarNam
def reverse_sort : FF<"reverse-sort", "Sort in reverse order">;
def size_sort : FF<"size-sort", "Sort symbols by size">;
def special_syms : FF<"special-syms", "Do not filter special symbols from the output">;
+def synthetic_syms : FF<"synthetic", "Include synthetic symbols in the output. These are special symbols created by the linker for various purposes">;
def undefined_only : FF<"undefined-only", "Show only undefined symbols">;
def version : FF<"version", "Display the version">;
def without_aliases : FF<"without-aliases", "Exclude aliases from output">, Flags<[HelpHidden]>;
diff --git a/llvm/tools/llvm-nm/llvm-nm.cpp b/llvm/tools/llvm-nm/llvm-nm.cpp
index ff07fbbaa5351..16db73c47f027 100644
--- a/llvm/tools/llvm-nm/llvm-nm.cpp
+++ b/llvm/tools/llvm-nm/llvm-nm.cpp
@@ -23,6 +23,7 @@
#include "llvm/Demangle/Demangle.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/LLVMContext.h"
+#include "llvm/MC/TargetRegistry.h"
#include "llvm/Object/Archive.h"
#include "llvm/Object/COFF.h"
#include "llvm/Object/COFFImportFile.h"
@@ -110,6 +111,7 @@ static bool PrintSize;
static bool Quiet;
static bool ReverseSort;
static bool SpecialSyms;
+static bool SyntheticSyms;
static bool SizeSort;
static bool UndefinedOnly;
static bool WithoutAliases;
@@ -1783,6 +1785,55 @@ getDynamicSyms(SymbolicFile &Obj) {
return E->getDynamicSymbolIterators();
}
+// Returns false if there is error found or true otherwise.
+static bool getPltSyms(SymbolicFile &Obj, std::vector<NMSymbol> &SymbolList) {
+ const auto *ELFObj = dyn_cast<ELFObjectFileBase>(&Obj);
+ if (!ELFObj)
+ return true;
+
+ std::string Err;
+ Triple TT;
+ TT.setArch(ELFObj->getArch());
+ TT.setOS(ELFObj->getOS());
+ const Target *TheTarget = TargetRegistry::lookupTarget(TT, Err);
+ if (!TheTarget) {
+ error("unable to find target for " + Obj.getFileName() + ": " + Err);
+ return false;
+ }
+
+ MCSubtargetInfo *STI = TheTarget->createMCSubtargetInfo(
+ TT.getTriple(), ELFObj->tryGetCPUName().value_or("").str(), "");
+ if (!STI) {
+ error("unable to create subtarget info for " + Obj.getFileName() + ": " +
+ Err);
+ return false;
+ }
+
+ for (auto Plt : ELFObj->getPltEntries(*STI)) {
+ if (Plt.Symbol) {
+ SymbolRef Symbol(*Plt.Symbol, ELFObj);
+ if (Expected<StringRef> NameOrErr = Symbol.getName()) {
+ if (!NameOrErr->empty()) {
+ NMSymbol S = {};
+ S.Address = Plt.Address;
+ S.Name = NameOrErr->str() + "@plt";
+ S.TypeChar = 'T';
+ S.SectionName = Plt.Section;
+ SymbolList.push_back(S);
+ }
+ } else {
+ consumeError(NameOrErr.takeError());
+ }
+ } else {
+ WithColor::warning(errs(), ToolName)
+ << "PLT entry at 0x" + Twine::utohexstr(Plt.Address)
+ << " references an invalid symbol";
+ }
+ }
+
+ return true;
+}
+
// Returns false if there is error found or true otherwise.
static bool getSymbolNamesFromObject(SymbolicFile &Obj,
std::vector<NMSymbol> &SymbolList) {
@@ -1807,6 +1858,12 @@ static bool getSymbolNamesFromObject(SymbolicFile &Obj,
<< toString(VersionsOrErr.takeError()) << "\n";
}
}
+
+ if (SyntheticSyms) {
+ if (!getPltSyms(Obj, SymbolList))
+ return false;
+ }
+
// If a "-s segname sectname" option was specified and this is a Mach-O
// file get the section number for that section in this object file.
unsigned int Nsect = 0;
@@ -2474,6 +2531,7 @@ int llvm_nm_main(int argc, char **argv, const llvm::ToolContext &) {
"(hexadecimal)");
SizeSort = Args.hasArg(OPT_size_sort);
SpecialSyms = Args.hasArg(OPT_special_syms);
+ SyntheticSyms = Args.hasArg(OPT_synthetic_syms);
UndefinedOnly = Args.hasArg(OPT_undefined_only);
WithoutAliases = Args.hasArg(OPT_without_aliases);
|
jh7370
reviewed
May 2, 2025
|
@jh7370 Hello! Sure, would add couple of lines to documentation. The build failures seems to be unrelated, all tests are passed, I would check out more precise a bit later. Thank you, waiting for your review! |
Compatible with GNU nm --syntethic option is used to show special symbols created by the linker. Current implementation is limited to show plt entries in the form of symbol@plt and plt entry address. Currently it would be used for BOLT testing purposes (llvm#135867) in order to eliminate external GNU nm dependency.
MaskRay
reviewed
May 2, 2025
| Type: STT_FUNC | ||
| Binding: STB_GLOBAL | ||
|
|
||
| # CHECK: 0000000000000600 T __cxa_finalize@plt |
There was a problem hiding this comment.
Testing two or three @plt should be sufficient.
You can define a function in b.so and reference it from a.c using clang a.c b.so -nostdlib to eliminate gmon_start/libc_start_main references
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I agree, if it is a major thing I would do it, just didn't want to waste time on this since 5 seems to be not a big issue :)
There was a problem hiding this comment.
Yes, it's a major thing. If you find patches to llvm-readobj/llvm-objdump, you will find @jh7370 and my requests to make tests minimal/sufficient to make test updating easier.
You could employ llvm/utils/update_test_body.py to make generating the test easier.
|
Thank you, beat me to it. Endorsing this, but deferring to binary utilities reviewers. |
MaskRay
reviewed
May 3, 2025
| .. option:: --synthetic | ||
| Include synthetic symbols in the output. Synthetic symbols are not present in | ||
| the original object file but are generated by the tool to represent relevant | ||
| runtime or linking information. |
There was a problem hiding this comment.
Perhaps
Include synthetic symbols in the output. Synthetic symbols are not present in the original object file. This currently includes symbols derived from PLT entries for ELF.
I find
"are generated by the tool to represent relevant runtime or linking information." very vague and not very useful. The PLT detail seems important.
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Compatible with GNU nm --syntethic option is used to show special
symbols created by the linker. Current implementation is limited to show
plt entries in the form of symbol@plt and plt entry address. Currently
it would be used for BOLT testing purposes
(#135867)
in order to eliminate external GNU nm dependency.