[llvm-readobj/llvm-readelf] - Implement GNU style dumper of the SHT_GNU_verneed section.

[grimar]

Summary

It was not implemented yet, we had only LLVM style dumper implemented.
Section description is here: https://refspecs.linuxfoundation.org/LSB_2.0.1/LSB-Core/LSB-Core/symverrqmts.html

[grimar]

• Fixed helper function name.

[MaskRay]

test/tools/llvm-readobj/elf-verneed-flags.yaml

1 ↗

(On Diff #201635)

delete the flags of ?

104 ↗

(On Diff #201635)

Probably elaborate a bit, .dynstr is required by .gnu.version_r

tools/llvm-readobj/ELFDumper.cpp

3436 ↗

(On Diff #201635)

Nit: " Addr: " (two spaces before "Addr:")

GNU readelf prints 0x prefix for .gnu.version_d and .gnu.version_r but omits the prefix for .gnu.version... I think the inconsistency may be due to a bug. We may stick with one style :)

[MaskRay]

Another thing: there is no new line between the text of .gnu.version_r and the text of .gnu.version_d.

[grimar]

In D62516#1520627, @MaskRay wrote:

Another thing: there is no new line between the text of .gnu.version_r and the text of .gnu.version_d.

I guess you mean between .gnu.version and .gnu.version_r? ( .gnu.version_d is implemented in a different patch).
I'll check.

[grimar]

• Addressed review comments.

test/tools/llvm-readobj/elf-verneed-flags.yaml

1 ↗

(On Diff #201635)

I am not sure. We check how we dump the versioning sections in elf-versioninfo.test.
But here my intention was to test how flags are dumped (verNeedFlagToString function logic).
I.e. if I remove the flags of it will probably be not so clear that this test is not a partial duplication of the elf-versioninfo.test.

tools/llvm-readobj/ELFDumper.cpp

3436 ↗

(On Diff #201635)

GNU output is:

Version symbols section '.gnu.version' contains 6 entries:
 Addr: 0000000000000000  Offset: 0x000280  Link: 7 (.dynsym)
readelf: Warning: Cannot interpret virtual addresses without program headers.
  000:457f              464c               102               901              
  004:   0 (*local*)       0 (*local*)    

Version definition section '.gnu.version_d' contains 3 entries:
  Addr: 0x0000000000000000  Offset: 0x00028c  Link: 8 (.dynstr)
  000000: Rev: 1  Flags: none  Index: 2  Cnt: 1  Name: VERSION1
  0x001c: Rev: 1  Flags: none  Index: 3  Cnt: 2  Name: VERSION2
  0x0038: Parent 1: VERSION1
readelf: Warning: Invalid vd_next field of 0

Version needs section '.gnu.version_r' contains 2 entries:
 Addr: 0x0000000000000000  Offset: 0x0002cc  Link: 8 (.dynstr)
  000000: Version: 1  File: verneed1.so.0  Cnt: 2
  0x0010:   Name: v1  Flags: none  Version: 4
  0x0020:   Name: v2  Flags: none  Version: 5
  0x0030: Version: 1  File: verneed2.so.0  Cnt: 1
  0x0040:   Name: v3  Flags: none  Version: 6

There are following inconsistencies can be observed:

1. Number of spaces before Addr. For .gnu.version_d there are 2, for other sections - 1.

So having a single space is a bit more consistent with GNU (2:1) :)

I would probably leave a single space, because this line is kind of prolog(header),
it is different from following entries (and hence can be separated).

2. 0x prefix, yes. As you mentioned, GNU omits it for .gnu.version, but not only that. It also does

it for the first entries. IMO looks ugly and crazy inconsistent. So I am always printing it.

[MaskRay]

tools/llvm-readobj/ELFDumper.cpp

3436 ↗

(On Diff #201635)

1 space looks good to me.

I didn't know the GNU output is so bad until you printed it out.. Pick the style that is aesthetically appealing then :)

000000 -> 0x0000 I believe this is also a GNU readelf bug.

[MaskRay]

tools/llvm-readobj/ELFDumper.cpp

3436 ↗

(On Diff #201635)

The readelf issue is almost fixed: https://sourceware.org/bugzilla/show_bug.cgi?id=24627

llvm/trunk/test/tools/llvm-readobj/elf-verneed-flags.yaml

+## Check how llvm-readobj/llvm-readelf tools dump the flags of SHT_GNU_verneed
+## section entries.
+
+# RUN: yaml2obj %s -o %t
+# RUN: llvm-readobj -V %t | FileCheck %s --check-prefix=LLVM-VERDEF
+# RUN: llvm-readelf -V %t | FileCheck %s --check-prefix=GNU-VERDEF
+
+# LLVM-VERDEF:      SHT_GNU_verneed {
+# LLVM-VERDEF-NEXT:   Dependency {
+# LLVM-VERDEF-NEXT:     Version: 1
+# LLVM-VERDEF-NEXT:     Count: 6
+# LLVM-VERDEF-NEXT:     FileName: dso.so.0
+# LLVM-VERDEF-NEXT:     Entries [
+# LLVM-VERDEF-NEXT:       Entry {
+# LLVM-VERDEF-NEXT:         Hash: 0
+# LLVM-VERDEF-NEXT:         Flags: Base (0x1)
+# LLVM-VERDEF-NEXT:         Index: 0
+# LLVM-VERDEF-NEXT:         Name: base
+# LLVM-VERDEF-NEXT:       }
+# LLVM-VERDEF-NEXT:       Entry {
+# LLVM-VERDEF-NEXT:         Hash: 0
+# LLVM-VERDEF-NEXT:         Flags: Weak (0x2)
+# LLVM-VERDEF-NEXT:         Index: 0
+# LLVM-VERDEF-NEXT:         Name: weak
+# LLVM-VERDEF-NEXT:       }
+# LLVM-VERDEF-NEXT:       Entry {
+# LLVM-VERDEF-NEXT:         Hash: 0
+# LLVM-VERDEF-NEXT:         Flags: Info (0x4)
+# LLVM-VERDEF-NEXT:         Index: 0
+# LLVM-VERDEF-NEXT:         Name: info
+# LLVM-VERDEF-NEXT:       }
+# LLVM-VERDEF-NEXT:       Entry {
+# LLVM-VERDEF-NEXT:         Hash: 0
+# LLVM-VERDEF-NEXT:         Flags: 0x7
+# LLVM-VERDEF-NEXT:         Index: 0
+# LLVM-VERDEF-NEXT:         Name: all
+# LLVM-VERDEF-NEXT:       }
+# LLVM-VERDEF-NEXT:       Entry {
+# LLVM-VERDEF-NEXT:         Hash: 0
+# LLVM-VERDEF-NEXT:         Flags: 0x8
+# LLVM-VERDEF-NEXT:         Index: 0
+# LLVM-VERDEF-NEXT:         Name: unknown
+# LLVM-VERDEF-NEXT:       }
+# LLVM-VERDEF-NEXT:       Entry {
+# LLVM-VERDEF-NEXT:         Hash: 0
+# LLVM-VERDEF-NEXT:         Flags: 0xF
+# LLVM-VERDEF-NEXT:         Index: 0
+# LLVM-VERDEF-NEXT:         Name: all_and_unknown
+# LLVM-VERDEF-NEXT:       }
+# LLVM-VERDEF-NEXT:     ]
+# LLVM-VERDEF-NEXT:   }
+# LLVM-VERDEF-NEXT: }
+
+# GNU-VERDEF:      Version needs section '.gnu.version_r' contains 1 entries:
+# GNU-VERDEF-NEXT:  Addr: 0000000000000000  Offset: 0x000200  Link: 6 (.dynstr)
+# GNU-VERDEF-NEXT:   0x0000: Version: 1  File: dso.so.0  Cnt: 6
+# GNU-VERDEF-NEXT:   0x0010:   Name: base  Flags: BASE  Version: 0
+# GNU-VERDEF-NEXT:   0x0020:   Name: weak  Flags: WEAK  Version: 0
+# GNU-VERDEF-NEXT:   0x0030:   Name: info  Flags: INFO  Version: 0
+# GNU-VERDEF-NEXT:   0x0040:   Name: all  Flags: BASE | WEAK | INFO  Version: 0
+# GNU-VERDEF-NEXT:   0x0050:   Name: unknown  Flags: <unknown>  Version: 0
+# GNU-VERDEF-NEXT:   0x0060:   Name: all_and_unknown  Flags: BASE | WEAK | INFO | <unknown>  Version: 0
+
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_EXEC
+  Machine:         EM_X86_64
+  Entry:           0x0000000000201000
+Sections:
+  - Name:            .gnu.version_r
+    Type:            SHT_GNU_verneed
+    Link:            .dynstr
+    Info:            0x0000000000000001
+    Dependencies:
+      - Version:         1
+        File:            dso.so.0
+        Entries:
+          - Name:            base
+            Hash:            0
+            Flags:           0x1
+            Other:           0
+          - Name:            weak
+            Hash:            0
+            Flags:           0x2
+            Other:           0
+          - Name:            info
+            Hash:            0
+            Flags:           0x4
+            Other:           0
+          - Name:            all
+            Hash:            0
+            Flags:           0x7
+            Other:           0
+          - Name:            unknown
+            Hash:            0
+            Flags:           0x8
+            Other:           0
+          - Name:            all_and_unknown
+            Hash:            0
+            Flags:           0xf
+            Other:           0
+## Needed to trigger .dynstr creation, which is required by .gnu.version_r
+DynamicSymbols:
+  - Name:    f1
+    Binding: STB_GLOBAL

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

 # LLVM-NEXT:     ]
 # LLVM-NEXT:   }
 # LLVM-NEXT: }
 
 # GNU:      Version symbols section '.gnu.version' contains 6 entries:
 # GNU-NEXT:  Addr: 0000000000000000  Offset: 0x000280  Link: 7 (.dynsym)
 # GNU-NEXT:   000:   0 (*local*) 2 (VERSION1) 3 (VERSION2) 4 (v1)
 # GNU-NEXT:   004:   5 (v2)      6 (v3)
-
-# GNU: Dumper for .gnu.version_d is not implemented
-# GNU: Dumper for .gnu.version_r is not implemented
+# GNU-EMPTY:
+# GNU-NEXT: Dumper for .gnu.version_d is not implemented
+# GNU-EMPTY:
+# GNU-NEXT: Version needs section '.gnu.version_r' contains 2 entries:
+# GNU-NEXT:  Addr: 0000000000000000  Offset: 0x0002cc  Link: 8 (.dynstr)
+# GNU-NEXT:   0x0000: Version: 1  File: verneed1.so.0  Cnt: 2
+# GNU-NEXT:   0x0010:   Name: v1  Flags: none  Version: 4
+# GNU-NEXT:   0x0020:   Name: v2  Flags: none  Version: 5
+# GNU-NEXT:   0x0030: Version: 1  File: verneed2.so.0  Cnt: 1
+# GNU-NEXT:   0x0040:   Name: v3  Flags: none  Version: 6

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

for (const Elf_Rel &Rel : DynPLTRelRegion.getAsArrayRef<Elf_Rel>()) {
       Rela.r_info = Rel.r_info;
       Rela.r_addend = 0;
       printDynamicRelocation(Obj, Rela, false);
     }
   }
 }
 
 template <class ELFT>
-void GNUStyle<ELFT>::printVersionSymbolSection(const ELFFile<ELFT> *Obj,
-                                               const Elf_Shdr *Sec) {
-  if (!Sec)
-    return;
-
+static void printGNUVersionSectionProlog(formatted_raw_ostream &OS,
+                                         const Twine &Name, unsigned EntriesNum,
+                                         const ELFFile<ELFT> *Obj,
+                                         const typename ELFT::Shdr *Sec) {
   StringRef SecName = unwrapOrError(Obj->getSectionName(Sec));
-  uint64_t Entries = Sec->sh_size / sizeof(Elf_Versym);
-
-  OS << "Version symbols section '" << SecName << "' "
-     << "contains " << Entries << " entries:\n";
+  OS << Name << " section '" << SecName << "' "
+     << "contains " << EntriesNum << " entries:\n";
 
-  const Elf_Shdr *SymTab = unwrapOrError(Obj->getSection(Sec->sh_link));
+  const typename ELFT::Shdr *SymTab =
+      unwrapOrError(Obj->getSection(Sec->sh_link));
   StringRef SymTabName = unwrapOrError(Obj->getSectionName(SymTab));
   OS << " Addr: " << format_hex_no_prefix(Sec->sh_addr, 16)
      << "  Offset: " << format_hex(Sec->sh_offset, 8)
      << "  Link: " << Sec->sh_link << " (" << SymTabName << ")\n";
+}
+
+template <class ELFT>
+void GNUStyle<ELFT>::printVersionSymbolSection(const ELFFile<ELFT> *Obj,
+                                               const Elf_Shdr *Sec) {
+  if (!Sec)
+    return;
+
+  unsigned Entries = Sec->sh_size / sizeof(Elf_Versym);
+  printGNUVersionSectionProlog(OS, "Version symbols", Entries, Obj, Sec);
 
   const uint8_t *VersymBuf =
       reinterpret_cast<const uint8_t *>(Obj->base() + Sec->sh_offset);
   const ELFDumper<ELFT> *Dumper = this->dumper();
   StringRef StrTable = Dumper->getDynamicStringTable();
 
   // readelf prints 4 entries per line.
   for (uint64_t VersymRow = 0; VersymRow < Entries; VersymRow += 4) {

 template <class ELFT>
 void GNUStyle<ELFT>::printVersionDefinitionSection(const ELFFile<ELFT> *Obj,
                                                    const Elf_Shdr *Sec) {
   if (!Sec)
     return;
 
   StringRef SecName = unwrapOrError(Obj->getSectionName(Sec));
   OS << "Dumper for " << SecName << " is not implemented\n";
+  OS << '\n';
+}
+
+static std::string verNeedFlagToString(unsigned Flags) {
+  if (Flags == 0)
+    return "none";
+
+  std::string Ret;
+  auto AddFlag = [&Ret, &Flags](unsigned Flag, StringRef Name) {
+    if (!(Flags & Flag))
+      return;
+    if (!Ret.empty())
+      Ret += " | ";
+    Ret += Name;
+    Flags &= ~Flag;
+  };
+
+  AddFlag(VER_FLG_BASE, "BASE");
+  AddFlag(VER_FLG_WEAK, "WEAK");
+  AddFlag(VER_FLG_INFO, "INFO");
+  AddFlag(~0, "<unknown>");
+  return Ret;
 }
 
 template <class ELFT>
 void GNUStyle<ELFT>::printVersionDependencySection(const ELFFile<ELFT> *Obj,
                                                    const Elf_Shdr *Sec) {
   if (!Sec)
     return;
 
-  StringRef SecName = unwrapOrError(Obj->getSectionName(Sec));
-  OS << "Dumper for " << SecName << " is not implemented\n";
+  unsigned VerneedNum = Sec->sh_info;
+  printGNUVersionSectionProlog(OS, "Version needs", VerneedNum, Obj, Sec);
+
+  ArrayRef<uint8_t> SecData = unwrapOrError(Obj->getSectionContents(Sec));
+
+  const Elf_Shdr *StrTabSec = unwrapOrError(Obj->getSection(Sec->sh_link));
+  StringRef StringTable = {
+      reinterpret_cast<const char *>(Obj->base() + StrTabSec->sh_offset),
+      StrTabSec->sh_size};
+
+  const uint8_t *VerneedBuf = SecData.data();
+  for (unsigned I = 0; I < VerneedNum; ++I) {
+    const Elf_Verneed *Verneed =
+        reinterpret_cast<const Elf_Verneed *>(VerneedBuf);
+
+    OS << format("  0x%04x: Version: %u  File: %s  Cnt: %u\n",
+                 reinterpret_cast<const uint8_t *>(Verneed) - SecData.begin(),
+                 (unsigned)Verneed->vn_version,
+                 StringTable.drop_front(Verneed->vn_file).data(),
+                 (unsigned)Verneed->vn_cnt);
+
+    const uint8_t *VernauxBuf = VerneedBuf + Verneed->vn_aux;
+    for (unsigned J = 0; J < Verneed->vn_cnt; ++J) {
+      const Elf_Vernaux *Vernaux =
+          reinterpret_cast<const Elf_Vernaux *>(VernauxBuf);
+
+      OS << format("  0x%04x:   Name: %s  Flags: %s  Version: %u\n",
+                   reinterpret_cast<const uint8_t *>(Vernaux) - SecData.begin(),
+                   StringTable.drop_front(Vernaux->vna_name).data(),
+                   verNeedFlagToString(Vernaux->vna_flags).c_str(),
+                   (unsigned)Vernaux->vna_other);
+      VernauxBuf += Vernaux->vna_next;
+    }
+    VerneedBuf += Verneed->vn_next;
+  }
+  OS << '\n';
 }
 
 // Hash histogram shows  statistics of how efficient the hash was for the
 // dynamic symbol table. The table shows number of hash buckets for different
 // lengths of chains as absolute number and percentage of the total buckets.
 // Additionally cumulative coverage of symbols for each set of buckets.
 template <class ELFT>
 void GNUStyle<ELFT>::printHashHistogram(const ELFFile<ELFT> *Obj) {