[llvm-readobj] - Teach llvm-readobj to dump .gnu.version_r sections

[grimar]

Summary

SHT_GNU_verneed (.gnu.version_r) is a version dependency section.
It was the last symbol versioning relative section that was not dumped,
now it is.

[• rafael]

LGTM with nits.

tools/llvm-readobj/ELFDumper.cpp

583 ↗

(On Diff #59734)

I don't think this should print Name/Address/Offset/Link. They are available from -s.

603 ↗

(On Diff #59734)

Not sure we need to print vn_cnt, since we print vn_cnt entries.

604 ↗

(On Diff #59734)

FileName maybe?

613 ↗

(On Diff #59734)

Don't we want to expand this into an enum?

[davide]

This looks fine after Rafael's comments are addressed.
I don't like "Version needs". Can we just use the original section name "SHT_GNU_verneed", which is more understandable and also maps 1:1 with the "spec"[1]? Rafael?

[1] When I say the spec I mean Drepper's document on versioning https://www.akkadia.org/drepper/symbol-versioning

[grimar]

Rafael, Davide, thanks for review !

tools/llvm-readobj/ELFDumper.cpp

583 ↗

(On Diff #59734)

Removed.

603 ↗

(On Diff #59734)

I would leave it. There can be lots of vn_aux and it can be reasonable to print the amount to know that value for possible testcases. Counting them all manually can be a problem.

604 ↗

(On Diff #59734)

Done.

613 ↗

(On Diff #59734)

Done. Btw according to gold sources I have, it is always 0 currently:

  for (p = this->need_versions_.begin(), i = 0;
       p != this->need_versions_.end();
       ++p, ++i)
    {
      elfcpp::Vernaux_write<size, big_endian> vna(pb);
      vna.set_vna_hash(Dynobj::elf_hash((*p)->version()));
      // FIXME: We need to sometimes set VER_FLG_WEAK here.
      vna.set_vna_flags(0);
      vna.set_vna_other((*p)->index());
      vna.set_vna_name(dynpool->get_offset((*p)->version()));
      vna.set_vna_next(i + 1 >= this->need_versions_.size()
		       ? 0
		       : vernaux_size);
      pb += vernaux_size;
    }

[• rafael]

rafael wrote:

Don't we want to expand this into an enum?

Done. Btw according to gold sources I have, it is always 0 currently:

Yes, according to
https://lists.debian.org/lsb-spec/1999/12/msg00017.html only
VER_FLG_WEAK is defined and it is not clear why it is needed.

The entire area around symbol versioning seems over designed and under
documented :-(

Cheers,
Rafael

[grimar]

Yes, according to
https://lists.debian.org/lsb-spec/1999/12/msg00017.html only
VER_FLG_WEAK is defined and it is not clear why it is needed.

The entire area around symbol versioning seems over designed and under
documented :-(

I have the same opinion here.
I suppose we just want to support minimal required subset in lld.

Cheers,
Rafael

llvm/trunk/test/tools/llvm-readobj/elf-versioninfo.test

 CHECK-NEXT:       Flags: 0
 CHECK-NEXT:       Index: 3
 CHECK-NEXT:       Cnt: 2
 CHECK-NEXT:       Hash: 175630258
 CHECK-NEXT:       Name: VERSION2
 CHECK-NEXT:     }
 CHECK-NEXT:   ]
 CHECK-NEXT: }
+
+RUN: llvm-readobj -V %p/Inputs/verneed.elf-x86-64 | FileCheck %s --check-prefix=VERNEED
+
+VERNEED:       SHT_GNU_verneed {
+VERNEED-NEXT:   Dependency {
+VERNEED-NEXT:     Version: 1
+VERNEED-NEXT:     Count: 2
+VERNEED-NEXT:     FileName: verneed1.so.0
+VERNEED-NEXT:     Entry {
+VERNEED-NEXT:       Hash: 1938
+VERNEED-NEXT:       Flags: 0x0
+VERNEED-NEXT:       Index: 3
+VERNEED-NEXT:       Name: v2
+VERNEED-NEXT:     }
+VERNEED-NEXT:     Entry {
+VERNEED-NEXT:       Hash: 1939
+VERNEED-NEXT:       Flags: 0x0
+VERNEED-NEXT:       Index: 2
+VERNEED-NEXT:       Name: v3
+VERNEED-NEXT:     }
+VERNEED-NEXT:   }
+VERNEED-NEXT:   Dependency {
+VERNEED-NEXT:     Version: 1
+VERNEED-NEXT:     Count: 1
+VERNEED-NEXT:     FileName: verneed2.so.0
+VERNEED-NEXT:     Entry {
+VERNEED-NEXT:       Hash: 1937
+VERNEED-NEXT:       Flags: 0x0
+VERNEED-NEXT:       Index: 4
+VERNEED-NEXT:       Name: v1
+VERNEED-NEXT:     }
+VERNEED-NEXT:   }
+VERNEED-NEXT: }

llvm/trunk/tools/llvm-readobj/ELFDumper.cpp

for (const typename ELFO::Elf_Sym &Sym : Dumper->dynamic_symbols()) {
     std::string FullSymbolName =
         Dumper->getFullSymbolName(&Sym, StrTable, true /* IsDynamic */);
     W.printNumber("Version", *P);
     W.printString("Name", FullSymbolName);
     P += sizeof(typename ELFO::Elf_Half);
   }
 }
 
+static const EnumEntry<unsigned> SymVersionFlags[] = {
+    {"Base", "BASE", VER_FLG_BASE},
+    {"Weak", "WEAK", VER_FLG_WEAK},
+    {"Info", "INFO", VER_FLG_INFO}};
+
 template <typename ELFO, class ELFT>
 static void printVersionDefinitionSection(ELFDumper<ELFT> *Dumper,
                                           const ELFO *Obj,
                                           const typename ELFO::Elf_Shdr *Sec,
                                           ScopedPrinter &W) {
   DictScope SD(W, "Version definition");
   if (!Sec)
     return;
for (unsigned i = 0; i < verdef_entries; ++i) {
     W.printNumber("Hash", VD->vd_hash);
     W.printString("Name",
                   StringRef((const char *)(Obj->base() + StrTab->sh_offset +
                                            VD->getAux()->vda_name)));
     P += VD->vd_next;
   }
 }
 
+template <typename ELFO, class ELFT>
+static void printVersionDependencySection(ELFDumper<ELFT> *Dumper,
+                                          const ELFO *Obj,
+                                          const typename ELFO::Elf_Shdr *Sec,
+                                          ScopedPrinter &W) {
+  typedef typename ELFO::Elf_Verneed VerNeed;
+  typedef typename ELFO::Elf_Vernaux VernAux;
+
+  DictScope SD(W, "SHT_GNU_verneed");
+  if (!Sec)
+    return;
+
+  unsigned VerNeedNum = 0;
+  for (const typename ELFO::Elf_Dyn &Dyn : Dumper->dynamic_table())
+    if (Dyn.d_tag == DT_VERNEEDNUM)
+      VerNeedNum = Dyn.d_un.d_val;
+
+  const uint8_t *SecData = (const uint8_t *)Obj->base() + Sec->sh_offset;
+  const typename ELFO::Elf_Shdr *StrTab =
+      unwrapOrError(Obj->getSection(Sec->sh_link));
+
+  const uint8_t *P = SecData;
+  for (unsigned I = 0; I < VerNeedNum; ++I) {
+    const VerNeed *Need = reinterpret_cast<const VerNeed *>(P);
+    DictScope Entry(W, "Dependency");
+    W.printNumber("Version", Need->vn_version);
+    W.printNumber("Count", Need->vn_cnt);
+    W.printString("FileName",
+                  StringRef((const char *)(Obj->base() + StrTab->sh_offset +
+                                           Need->vn_file)));
+
+    const uint8_t *PAux = P + Need->vn_aux;
+    for (unsigned J = 0; J < Need->vn_cnt; ++J) {
+      const VernAux *Aux = reinterpret_cast<const VernAux *>(PAux);
+      DictScope Entry(W, "Entry");
+      W.printNumber("Hash", Aux->vna_hash);
+      W.printEnum("Flags", Aux->vna_flags, makeArrayRef(SymVersionFlags));
+      W.printNumber("Index", Aux->vna_other);
+      W.printString("Name",
+                    StringRef((const char *)(Obj->base() + StrTab->sh_offset +
+                                             Aux->vna_name)));
+      PAux += Aux->vna_next;
+    }
+    P += Need->vn_next;
+  }
+}
+
 template <typename ELFT> void ELFDumper<ELFT>::printVersionInfo() {
   // Dump version symbol section.
   printVersionSymbolSection(this, Obj, dot_gnu_version_sec, W);
 
   // Dump version definition section.
   printVersionDefinitionSection(this, Obj, dot_gnu_version_d_sec, W);
+
+  // Dump version dependency section.
+  printVersionDependencySection(this, Obj, dot_gnu_version_r_sec, W);
 }
 
 template <typename ELFT>
 StringRef ELFDumper<ELFT>::getSymbolVersion(StringRef StrTab,
                                             const Elf_Sym *symb,
                                             bool &IsDefault) const {
   // This is a dynamic symbol. Look in the GNU symbol version table.
   if (!dot_gnu_version_sec) {