Commit 5f8e51a9 authored by Georgii Rymar's avatar Georgii Rymar
Browse files

[llvm-readobj] - Add a few warnings for --gnu-hash-table. 

The current implementation stops dumping in case of a single error
it handles, though we can continue dumping.
This patch refines it: it adds a few warnings and a few test cases.

Differential revision: https://reviews.llvm.org/D73269
parent 7fd7a9a6

llvm/test/tools/llvm-readobj/ELF/gnuhash.test

+214 −0
Original line number Diff line number Diff line
@@ -100,3 +100,217 @@ ProgramHeaders: 
    Sections:

      - Section: .gnu.hash

      - Section: .dynamic



## Check we report a warning if there is no dynamic symbol section in the object.



# RUN: yaml2obj --docnum=3 %s -o %t.nodynsym

# RUN: llvm-readobj --gnu-hash-table %t.nodynsym 2>&1 | FileCheck %s -DFILE=%t.nodynsym --check-prefix=NODYNSYM

# RUN: llvm-readelf --gnu-hash-table %t.nodynsym 2>&1 | FileCheck %s -DFILE=%t.nodynsym --check-prefix=NODYNSYM



# NODYNSYM:      GnuHashTable {

# NODYNSYM-NEXT:   Num Buckets: 1

# NODYNSYM-NEXT:   First Hashed Symbol Index: 0

# NODYNSYM-NEXT:   Num Mask Words: 1

# NODYNSYM-NEXT:   Shift Count: 0

# NODYNSYM-NEXT:   Bloom Filter: [0x0]

# NODYNSYM-NEXT:   Buckets: [0]

# NODYNSYM-NEXT: warning: '[[FILE]]': unable to dump 'Values' for the SHT_GNU_HASH section: no dynamic symbol table found

# NODYNSYM-NEXT: }



--- !ELF

FileHeader:

  Class:   ELFCLASS64

  Data:    ELFDATA2LSB

  Type:    ET_DYN

  Machine: EM_X86_64

Sections:

  - Name:  .gnu.hash

    Type:  SHT_GNU_HASH

    Flags: [ SHF_ALLOC ]

    Header:

      SymNdx: 0x0

      Shift2: 0x0

    BloomFilter: [ 0x0 ]

    HashBuckets: [ 0x0 ]

    HashValues:  [ 0x0 ]

  - Name:  .dynamic

    Type:  SHT_DYNAMIC

    Flags: [ SHF_ALLOC ]

    Entries:

      - Tag:   DT_GNU_HASH

        Value: 0x0

      - Tag:   DT_NULL

        Value: 0x0

ProgramHeaders:

  - Type:  PT_LOAD

    Flags: [ PF_R, PF_X ]

    Sections:

      - Section: .gnu.hash

      - Section: .dynamic



## Check what we do when the index of the first symbol in the dynamic symbol table

## included in the hash table is larger than the number of dynamic symbols.



# RUN: yaml2obj --docnum=4 %s -o %t.brokensymndx

# RUN: llvm-readobj --gnu-hash-table %t.brokensymndx 2>&1 \

# RUN:   | FileCheck %s -DFILE=%t.brokensymndx --check-prefix=SYMNDX

# RUN: llvm-readelf --gnu-hash-table %t.brokensymndx 2>&1 \

# RUN:   | FileCheck %s -DFILE=%t.brokensymndx --check-prefix=SYMNDX



# SYMNDX:      GnuHashTable {

# SYMNDX-NEXT:   Num Buckets: 1

# SYMNDX-NEXT:   First Hashed Symbol Index: 2

# SYMNDX-NEXT:   Num Mask Words: 1

# SYMNDX-NEXT:   Shift Count: 0

# SYMNDX-NEXT:   Bloom Filter: [0x1]

# SYMNDX-NEXT:   Buckets: [2]

# SYMNDX-NEXT: warning: '[[FILE]]': the first hashed symbol index (2) is larger than the number of dynamic symbols (2)

# SYMNDX-NEXT: }



--- !ELF

FileHeader:

  Class:   ELFCLASS64

  Data:    ELFDATA2LSB

  Type:    ET_DYN

  Machine: EM_X86_64

Sections:

  - Name:  .gnu.hash

    Type:  SHT_GNU_HASH

    Flags: [ SHF_ALLOC ]

    Header:

      SymNdx: 0x2

      Shift2: 0x0

    BloomFilter: [ 0x1 ]

    HashBuckets: [ 0x2 ]

    HashValues:  [ 0x3 ]

  - Name:  .dynamic

    Type:  SHT_DYNAMIC

    Flags: [ SHF_ALLOC ]

    Link:  0

    Entries:

      - Tag:   DT_GNU_HASH

        Value: 0x0

      - Tag:   DT_NULL

        Value: 0x0

DynamicSymbols:

  - Name:    aaa

    Binding: STB_GLOBAL

ProgramHeaders:

  - Type:  PT_LOAD

    Flags: [ PF_R, PF_X ]

    Sections:

      - Section: .gnu.hash

      - Section: .dynamic



## Check we emit a warning when the dynamic symbol table is empty.

## A valid dynamic symbol table should have at least one symbol: the symbol with index 0.



# RUN: yaml2obj --docnum=5 %s -o %t.emptydynsym

# RUN: llvm-readobj --gnu-hash-table %t.emptydynsym 2>&1 \

# RUN:   | FileCheck %s -DFILE=%t.emptydynsym --check-prefix=EMPTY-DYNSYM

# RUN: llvm-readelf --gnu-hash-table %t.emptydynsym 2>&1 \

# RUN:   | FileCheck %s -DFILE=%t.emptydynsym --check-prefix=EMPTY-DYNSYM



# EMPTY-DYNSYM:      GnuHashTable {

# EMPTY-DYNSYM-NEXT:   Num Buckets: 1

# EMPTY-DYNSYM-NEXT:   First Hashed Symbol Index: 0

# EMPTY-DYNSYM-NEXT:   Num Mask Words: 1

# EMPTY-DYNSYM-NEXT:   Shift Count: 0

# EMPTY-DYNSYM-NEXT:   Bloom Filter: [0x0]

# EMPTY-DYNSYM-NEXT:   Buckets: [0]

# EMPTY-DYNSYM-NEXT: warning: '[[FILE]]': unable to dump 'Values' for the SHT_GNU_HASH section: the dynamic symbol table is empty

# EMPTY-DYNSYM-NEXT: }



--- !ELF

FileHeader:

  Class:   ELFCLASS64

  Data:    ELFDATA2LSB

  Type:    ET_DYN

  Machine: EM_X86_64

Sections:

  - Name:  .gnu.hash

    Type:  SHT_GNU_HASH

    Flags: [ SHF_ALLOC ]

    Header:

      SymNdx: 0x0

      Shift2: 0x0

    BloomFilter: [ 0x0 ]

    HashBuckets: [ 0x0 ]

    HashValues:  [ 0x0 ]

  - Name:  .dynamic

    Type:  SHT_DYNAMIC

    Flags: [ SHF_ALLOC ]

    Link:  0

    Entries:

      - Tag:   DT_GNU_HASH

        Value: 0x0

      - Tag:   DT_NULL

        Value: 0x0

  - Name: .dynsym

    Type: SHT_DYNSYM

    Size: 0

ProgramHeaders:

  - Type:  PT_LOAD

    Flags: [ PF_R, PF_X ]

    Sections:

      - Section: .gnu.hash

      - Section: .dynamic



## Linkers might produce an empty no-op SHT_GNU_HASH section when

## there are no dynamic symbols or when all dynamic symbols are undefined.

## Such sections normally have a single zero entry in the bloom

## filter, a single zero entry in the hash bucket and no values.

##

## The index of the first symbol in the dynamic symbol table

## included in the hash table can be set to the number of dynamic symbols,

## which is one larger than the index of the last dynamic symbol.

## For empty tables however, this value is unimportant and can be ignored.



# RUN: yaml2obj --docnum=6 %s -o %t.empty

# RUN: llvm-readobj --gnu-hash-table %t.empty 2>&1 \

# RUN:   | FileCheck %s -DFILE=%t.empty --check-prefix=EMPTY --implicit-check-not="warning:"

# RUN: llvm-readelf --gnu-hash-table %t.empty 2>&1 \

# RUN:   | FileCheck %s -DFILE=%t.empty --check-prefix=EMPTY --implicit-check-not="warning:"



# EMPTY:      GnuHashTable {

# EMPTY-NEXT:   Num Buckets: 1

# EMPTY-NEXT:   First Hashed Symbol Index: 1

# EMPTY-NEXT:   Num Mask Words: 1

# EMPTY-NEXT:   Shift Count: 0

# EMPTY-NEXT:   Bloom Filter: [0x0]

# EMPTY-NEXT:   Buckets: [0]

# EMPTY-NEXT:   Values: []

# EMPTY-NEXT: }



--- !ELF

FileHeader:

  Class:   ELFCLASS64

  Data:    ELFDATA2LSB

  Type:    ET_DYN

  Machine: EM_X86_64

Sections:

  - Name:  .gnu.hash

    Type:  SHT_GNU_HASH

    Flags: [ SHF_ALLOC ]

    Header:

      SymNdx: 0x1

      Shift2: 0x0

    BloomFilter: [ 0x0 ]

    HashBuckets: [ 0x0 ]

    HashValues:  [ ]

  - Name:  .dynamic

    Type:  SHT_DYNAMIC

    Flags: [ SHF_ALLOC ]

    Link:  0

    Entries:

      - Tag:   DT_GNU_HASH

        Value: 0x0

      - Tag:   DT_NULL

        Value: 0x0

DynamicSymbols: []

ProgramHeaders:

  - Type:  PT_LOAD

    Flags: [ PF_R, PF_X ]

    Sections:

      - Section: .gnu.hash

      - Section: .dynamic

llvm/tools/llvm-readobj/ELFDumper.cpp

+44 −6
Original line number Diff line number Diff line
@@ -2495,12 +2495,50 @@ template <typename ELFT> void ELFDumper<ELFT>::printGnuHashTable() { 
  W.printNumber("First Hashed Symbol Index", GnuHashTable->symndx);

  W.printNumber("Num Mask Words", GnuHashTable->maskwords);

  W.printNumber("Shift Count", GnuHashTable->shift2);

  W.printHexList("Bloom Filter", GnuHashTable->filter());

  W.printList("Buckets", GnuHashTable->buckets());

  Elf_Sym_Range Syms = dynamic_symbols();

  unsigned NumSyms = std::distance(Syms.begin(), Syms.end());

  if (!NumSyms)

    reportError(createError("No dynamic symbol section"), ObjF->getFileName());



  ArrayRef<typename ELFT::Off> BloomFilter = GnuHashTable->filter();

  W.printHexList("Bloom Filter", BloomFilter);



  ArrayRef<Elf_Word> Buckets = GnuHashTable->buckets();

  W.printList("Buckets", Buckets);



  if (!DynSymRegion.Addr) {

    reportWarning(createError("unable to dump 'Values' for the SHT_GNU_HASH "

                              "section: no dynamic symbol table found"),

                  ObjF->getFileName());

    return;

  }



  size_t NumSyms = dynamic_symbols().size();

  if (!NumSyms) {

    reportWarning(createError("unable to dump 'Values' for the SHT_GNU_HASH "

                              "section: the dynamic symbol table is empty"),

                  ObjF->getFileName());

    return;

  }



  if (GnuHashTable->symndx >= NumSyms) {

    // A normal empty GNU hash table section produced by linker might have

    // symndx set to the number of dynamic symbols + 1 (for the zero symbol)

    // and have dummy null values in the Bloom filter and in the buckets

    // vector. It happens because the value of symndx is not important for

    // dynamic loaders when the GNU hash table is empty. They just skip the

    // whole object during symbol lookup. In such cases, the symndx value is

    // irrelevant and we should not report a warning.

    bool IsEmptyHashTable =

        llvm::all_of(Buckets, [](Elf_Word V) { return V == 0; });



    if (!IsEmptyHashTable) {

      reportWarning(

          createError("the first hashed symbol index (" +

                      Twine(GnuHashTable->symndx) +

                      ") is larger than the number of dynamic symbols (" +

                      Twine(NumSyms) + ")"),

          ObjF->getFileName());

      return;

    }

  }



  W.printHexList("Values", GnuHashTable->values(NumSyms));

}