[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);
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@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.
| Type: STT_FUNC | ||
| Binding: STB_GLOBAL | ||
|
|
||
| # CHECK: 0000000000000600 T __cxa_finalize@plt |
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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 :)
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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.
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Thank you, beat me to it. Endorsing this, but deferring to binary utilities reviewers. |
| .. 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. |
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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.
Some testing configurations don't support `nm --synthetic` option (where nm is a symlink to llvm-nm), which prevents us from resolving `puts@plt` symbol address in profile generation inside the test. Disable the check until llvm-nm support is landed (#138232). Test Plan: bin/llvm-lit -a tools/bolt/test/X86/callcont-fallthru.s
…m#140026) PR llvm#139953 used `DONTRUN` to disable some run lines, but that didn't work. Now switching to `RUN-DISABLED` for disabling the tests until llvm-nm support is landed (llvm#138232).
| Flags: [ SHF_ALLOC, SHF_EXECINSTR ] | ||
| Address: 0x5D0 | ||
| AddressAlign: 0x10 | ||
| Content: F07BBFA99000009011D247F910823E9120021FD61F2003D51F2003D51F2003D59000009011D647F910A23E9120021FD69000009011DA47F910C23E9120021FD69000009011DE47F910E23E9120021FD69000009011E247F910023F9120021FD69000009011E647F910223F9120021FD6 |
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I think a comment illustrating why this and the .got have the contents they do could be useful for helping future test readers/maintainers.
| @@ -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">; | |||
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| def synthetic_syms : FF<"synthetic", "Include synthetic symbols in the output. These are special symbols created by the linker for various purposes">; | |
| def synthetic_syms : FF<"synthetic", "Include synthetic symbols in the output. These are special symbols created by the linker for various purposes">; |
Since this is rendered as monospace font on the command-line, a double space here will look ugly. Also, please reflow this option so it spreads over multiple lines, since it is rather long.
| @@ -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) { | |||
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I think it would be better for this function to return Error and for the caller to report the error. Perhaps even try Expected<std::vector<NMSymbol>> rather than using a parameter to record the results in, but that may not be a good idea, for performance reasons, depending on the size of the vector you'd often expect.
| TT.setOS(ELFObj->getOS()); | ||
| const Target *TheTarget = TargetRegistry::lookupTarget(TT, Err); | ||
| if (!TheTarget) { | ||
| error("unable to find target for " + Obj.getFileName() + ": " + Err); |
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Could you give an example of what the full error message looks like, if e.g. you use llvm-nm built without X86_64 support with one that does support that target, please? I'd like to be sure the message isn't too clunky.
| return false; | ||
| } | ||
|
|
||
| for (auto Plt : ELFObj->getPltEntries(*STI)) { |
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LLVM style guide says to only use auto where it improves readability. As things stand, I can't tell what the type of Plt is here, which means it's harming readability here and should be expanded. Also, using auto here doesn't convey whether this is a reference or not, when it probably should be const &.
| SymbolList.push_back(S); | ||
| } | ||
| } else { | ||
| consumeError(NameOrErr.takeError()); |
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Is there a reason why this isn't a warning?
| if (Plt.Symbol) { | ||
| SymbolRef Symbol(*Plt.Symbol, ELFObj); | ||
| if (Expected<StringRef> NameOrErr = Symbol.getName()) { | ||
| if (!NameOrErr->empty()) { |
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I think it's a little unfortunate that we're just ignoring such symbols. Perhaps it should be a warning too, or you could actually use it as an empty string (so you'd get @plt simply as the name). The latter feels most appropriate to me without thinking too hard about it at the moment.
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.