[llvm-readelf] --section-details: display SHF_COMPRESSED headers

[MaskRay]

Summary

readelf --section-details displays ch_type/ch_size/ch_addralign for
a SHF_COMPRESSED section. Port the feature. There is a small difference
that readelf doesn't display [<corrupt>] for an empty section while
we do.

[jhenderson]

llvm/tools/llvm-readobj/ELFDumper.cpp

4196

I'm wondering if we should report this error as a warning. It might help the user know why their section is corrupt, for example.

[MaskRay]

llvm/tools/llvm-readobj/ELFDumper.cpp

4196

The GNU behavior is [<corrupt>]. Do you suggest a separate warning beside the stdout output? That may duplicate the information...

[jhenderson]

llvm/tools/llvm-readobj/ELFDumper.cpp

4196

Yes, that's what I'm suggesting. For example, we already have in llvm-readelf warnings when the code can't read a section name, but we still print a placeholder for the name (e.g. <no-strings> in https://github.com/llvm/llvm-project/blob/main/llvm/test/tools/llvm-readobj/ELF/sections-no-section-header-string-table.test).

[MaskRay]

add a warning

[jhenderson]

LGTM!

llvm/include/llvm/Object/ELFTypes.h

#define LLVM_ELF_IMPORT_TYPES_ELFT(ELFT)                                       \
   using Elf_Relr = typename ELFT::Relr;                                        \
   using Elf_Verdef = typename ELFT::Verdef;                                    \
   using Elf_Verdaux = typename ELFT::Verdaux;                                  \
   using Elf_Verneed = typename ELFT::Verneed;                                  \
   using Elf_Vernaux = typename ELFT::Vernaux;                                  \
   using Elf_Versym = typename ELFT::Versym;                                    \
   using Elf_Hash = typename ELFT::Hash;                                        \
   using Elf_GnuHash = typename ELFT::GnuHash;                                  \
+  using Elf_Chdr = typename ELFT::Chdr;                                        \
   using Elf_Nhdr = typename ELFT::Nhdr;                                        \
   using Elf_Note = typename ELFT::Note;                                        \
   using Elf_Note_Iterator = typename ELFT::NoteIterator;                       \
   using Elf_CGProfile = typename ELFT::CGProfile;                              \
   using Elf_Dyn_Range = typename ELFT::DynRange;                               \
   using Elf_Shdr_Range = typename ELFT::ShdrRange;                             \
   using Elf_Sym_Range = typename ELFT::SymRange;                               \
   using Elf_Rel_Range = typename ELFT::RelRange;                               \

llvm/test/tools/llvm-readobj/ELF/section-details.test

 ## Check how llvm-readelf prints section details with --section-details.
 
 ## Check the output for the 64-bit case.
-# RUN: yaml2obj %s -DBITS=64 -o %t64.o
-# RUN: llvm-readelf %t64.o --section-details | \
-# RUN:   FileCheck %s --strict-whitespace --match-full-lines --check-prefix=GNU64
+# RUN: yaml2obj %s -DBITS=64 -DCHDR=0000000008000000000000000400000000000000 -o %t64.o
+# RUN: llvm-readelf %t64.o --section-details 2>&1 | \
+# RUN:   FileCheck %s -DFILE=%t64.o --strict-whitespace --match-full-lines --check-prefix=GNU64
 
-#       GNU64:There are 19 section headers, starting at offset 0xf8:
+#       GNU64:There are 22 section headers, starting at offset 0x198:
 # GNU64-EMPTY:
 #  GNU64-NEXT:Section Headers:
 #  GNU64-NEXT:  [Nr] Name
 #  GNU64-NEXT:       Type            Address          Off    Size   ES   Lk Inf Al
 #  GNU64-NEXT:       Flags
 #  GNU64-NEXT:  [ 0] {{$}}
 #  GNU64-NEXT:       NULL            0000000000000000 000000 000000 00   0   0  0
 #  GNU64-NEXT:       [0000000000000000]: {{$}}
 #  GNU64-NEXT:  [ 1] allflags_and_long_fields
 #  GNU64-NEXT:       PROGBITS        1111111111111111 2222222222222222 4444444444444444 5555555555555555 858993459 1717986918 8608480567731124087
 #  GNU64-NEXT:       [ffffffffffffffff]: WRITE, ALLOC, EXEC, MERGE, STRINGS, INFO LINK, LINK ORDER, OS NONCONF, GROUP, TLS, COMPRESSED, EXCLUDE, OS (000000000ff00000), PROC (0000000070000000), UNKNOWN (ffffffff000ff008)
+#  GNU64-NEXT:{{.*}}: warning: '[[FILE]]': SHF_COMPRESSED section 'allflags_and_long_fields' does not have an Elf_Chdr header
+#  GNU64-NEXT:       [<corrupt>]
 #  GNU64-NEXT:  [ 2] noflags
 #  GNU64-NEXT:       PROGBITS        0000000000000000 000040 000000 00   0   0  0
 #  GNU64-NEXT:       [0000000000000000]: {{$}}
 #  GNU64-NEXT:  [ 3] write
 #  GNU64-NEXT:       PROGBITS        0000000000000000 000040 000000 00   0   0  0
 #  GNU64-NEXT:       [0000000000000001]: WRITE
 #  GNU64-NEXT:  [ 4] alloc
 #  GNU64-NEXT:       PROGBITS        0000000000000000 000040 000000 00   0   0  0

 #  GNU64-NEXT:       PROGBITS        0000000000000000 000040 000000 00   0   0  0
 #  GNU64-NEXT:       [0000000000000100]: OS NONCONF
 #  GNU64-NEXT:  [11] group
 #  GNU64-NEXT:       PROGBITS        0000000000000000 000040 000000 00   0   0  0
 #  GNU64-NEXT:       [0000000000000200]: GROUP
 #  GNU64-NEXT:  [12] tls
 #  GNU64-NEXT:       PROGBITS        0000000000000000 000040 000000 00   0   0  0
 #  GNU64-NEXT:       [0000000000000400]: TLS
-#  GNU64-NEXT:  [13] compressed
-#  GNU64-NEXT:       PROGBITS        0000000000000000 000040 000000 00   0   0  0
-#  GNU64-NEXT:       [0000000000000800]: COMPRESSED
-#  GNU64-NEXT:  [14] exclude
+#  GNU64-NEXT:  [13] exclude
 #  GNU64-NEXT:       PROGBITS        0000000000000000 000040 000000 00   0   0  0
 #  GNU64-NEXT:       [0000000080000000]: EXCLUDE
-#  GNU64-NEXT:  [15] known_and_unknown
+#  GNU64-NEXT:  [14] known_and_unknown
 #  GNU64-NEXT:       PROGBITS        0000000000000000 000040 000000 00   0   0  0
 #  GNU64-NEXT:       [00000000000f0003]: WRITE, ALLOC, UNKNOWN (00000000000f0000)
-#  GNU64-NEXT:  [16] only_unknown
+#  GNU64-NEXT:  [15] only_unknown
 #  GNU64-NEXT:       PROGBITS        0000000000000000 000040 000000 00   0   0  0
 #  GNU64-NEXT:       [00000000000f0000]: UNKNOWN (00000000000f0000)
-#  GNU64-NEXT:  [17] .strtab
-#  GNU64-NEXT:       STRTAB          0000000000000000 000040 000001 00   0   0  1
+#  GNU64-NEXT:  [16] compressed_corrupted
+#  GNU64-NEXT:       PROGBITS        0000000000000000 000040 000000 00   0   0  0
+#  GNU64-NEXT:       [0000000000000800]: COMPRESSED
+#  GNU64-NEXT:{{.*}}: warning: '[[FILE]]': SHF_COMPRESSED section 'compressed_corrupted' does not have an Elf_Chdr header
+#  GNU64-NEXT:       [<corrupt>]
+#  GNU64-NEXT:  [17] compressed_zlib
+#  GNU64-NEXT:       PROGBITS        0000000000000000 000040 000023 00   0   0  0
+#  GNU64-NEXT:       [0000000000000800]: COMPRESSED
+#  GNU64-NEXT:       ZLIB, 0000000000000008, 4
+#  GNU64-NEXT:  [18] compressed_zstd
+#  GNU64-NEXT:       PROGBITS        0000000000000000 000063 000029 00   0   0  0
+#  GNU64-NEXT:       [0000000000000800]: COMPRESSED
+#  GNU64-NEXT:       ZSTD, 0000000000000008, 4
+#  GNU64-NEXT:  [19] compressed_unknown
+#  GNU64-NEXT:       PROGBITS        0000000000000000 00008c 000018 00   0   0  0
+#  GNU64-NEXT:       [0000000000000800]: COMPRESSED
+#  GNU64-NEXT:       [<unknown>: 0x3], 0000000000000008, 4
+#  GNU64-NEXT:  [20] .strtab
+#  GNU64-NEXT:       STRTAB          0000000000000000 0000a4 000001 00   0   0  1
 #  GNU64-NEXT:       [0000000000000000]: {{$}}
-#  GNU64-NEXT:  [18] .shstrtab
-#  GNU64-NEXT:       STRTAB          0000000000000000 000041 0000b0 00   0   0  1
+#  GNU64-NEXT:  [21] .shstrtab
+#  GNU64-NEXT:       STRTAB          0000000000000000 0000a5 0000ed 00   0   0  1
 #  GNU64-NEXT:       [0000000000000000]: {{$}}
 #  GNU64-NOT:{{.}}
 
 --- !ELF
 FileHeader:
   Class: ELFCLASS[[BITS]]
   Data:  ELFDATA2LSB
   Type:  ET_REL
- Name:  nonconforming
     Type:  SHT_PROGBITS
     Flags: [ SHF_OS_NONCONFORMING ]
   - Name:  group
     Type:  SHT_PROGBITS
     Flags: [ SHF_GROUP ]
   - Name:  tls
     Type:  SHT_PROGBITS
     Flags: [ SHF_TLS ]
-  - Name:  compressed
-    Type:  SHT_PROGBITS
-    Flags: [ SHF_COMPRESSED ]
   - Name:  exclude
     Type:  SHT_PROGBITS
     Flags: [ SHF_EXCLUDE ]
   - Name:  known_and_unknown
     Type:  SHT_PROGBITS
     ShFlags: 0x000f0003
   - Name:  only_unknown
     Type:  SHT_PROGBITS
     ShFlags: 0x000f0000
+  - Name:  compressed_corrupted
+    Type:  SHT_PROGBITS
+    Flags: [ SHF_COMPRESSED ]
+  - Name:  compressed_zlib
+    Type:  SHT_PROGBITS
+    Flags: [ SHF_COMPRESSED ]
+    Content: 01000000[[CHDR]]789c636080000000080001
+  - Name:  compressed_zstd
+    Type:  SHT_PROGBITS
+    Flags: [ SHF_COMPRESSED ]
+    Content: 02000000[[CHDR]]28b52ffd20084100000000000000000000
+  - Name:  compressed_unknown
+    Type:  SHT_PROGBITS
+    Flags: [ SHF_COMPRESSED ]
+    Content: 03000000[[CHDR]]
 
 ## Check the output for the 32-bit case.
-# RUN: yaml2obj %s -DBITS=32 -o %t32.o
-# RUN: llvm-readelf %t32.o --section-details | \
-# RUN:   FileCheck %s --strict-whitespace --match-full-lines --check-prefix=GNU32
+# RUN: yaml2obj %s -DBITS=32 -DCHDR=0400000002000000 -o %t32.o
+# RUN: llvm-readelf %t32.o --section-details 2>&1 | \
+# RUN:   FileCheck %s -DFILE=%t32.o --strict-whitespace --match-full-lines --check-prefix=GNU32
 
-#       GNU32:There are 19 section headers, starting at offset 0xe8:
+#       GNU32:There are 22 section headers, starting at offset 0x164:
 # GNU32-EMPTY:
 #  GNU32-NEXT:Section Headers:
 #  GNU32-NEXT:  [Nr] Name
 #  GNU32-NEXT:       Type            Addr     Off    Size   ES   Lk Inf Al
 #  GNU32-NEXT:       Flags
 #  GNU32-NEXT:  [ 0] {{$}}
 #  GNU32-NEXT:       NULL            00000000 000000 000000 00   0   0  0
 #  GNU32-NEXT:       [00000000]: {{$}}
 #  GNU32-NEXT:  [ 1] allflags_and_long_fields
 #  GNU32-NEXT:       PROGBITS        11111111 22222222 44444444 55555555 858993459 1717986918 2004318071
 #  GNU32-NEXT:       [ffffffff]: WRITE, ALLOC, EXEC, MERGE, STRINGS, INFO LINK, LINK ORDER, OS NONCONF, GROUP, TLS, COMPRESSED, EXCLUDE, OS (0ff00000), PROC (70000000), UNKNOWN (000ff008)
+#  GNU32-NEXT:{{.*}}: warning: '[[FILE]]': SHF_COMPRESSED section 'allflags_and_long_fields' does not have an Elf_Chdr header
+#  GNU32-NEXT:       [<corrupt>]
 #  GNU32-NEXT:  [ 2] noflags
 #  GNU32-NEXT:       PROGBITS        00000000 000034 000000 00   0   0  0
 #  GNU32-NEXT:       [00000000]: {{$}}
 #  GNU32-NEXT:  [ 3] write
 #  GNU32-NEXT:       PROGBITS        00000000 000034 000000 00   0   0  0
 #  GNU32-NEXT:       [00000001]: WRITE
 #  GNU32-NEXT:  [ 4] alloc
 #  GNU32-NEXT:       PROGBITS        00000000 000034 000000 00   0   0  0

 #  GNU32-NEXT:       PROGBITS        00000000 000034 000000 00   0   0  0
 #  GNU32-NEXT:       [00000100]: OS NONCONF
 #  GNU32-NEXT:  [11] group
 #  GNU32-NEXT:       PROGBITS        00000000 000034 000000 00   0   0  0
 #  GNU32-NEXT:       [00000200]: GROUP
 #  GNU32-NEXT:  [12] tls
 #  GNU32-NEXT:       PROGBITS        00000000 000034 000000 00   0   0  0
 #  GNU32-NEXT:       [00000400]: TLS
-#  GNU32-NEXT:  [13] compressed
-#  GNU32-NEXT:       PROGBITS        00000000 000034 000000 00   0   0  0
-#  GNU32-NEXT:       [00000800]: COMPRESSED
-#  GNU32-NEXT:  [14] exclude
+#  GNU32-NEXT:  [13] exclude
 #  GNU32-NEXT:       PROGBITS        00000000 000034 000000 00   0   0  0
 #  GNU32-NEXT:       [80000000]: EXCLUDE
-#  GNU32-NEXT:  [15] known_and_unknown
+#  GNU32-NEXT:  [14] known_and_unknown
 #  GNU32-NEXT:       PROGBITS        00000000 000034 000000 00   0   0  0
 #  GNU32-NEXT:       [000f0003]: WRITE, ALLOC, UNKNOWN (000f0000)
-#  GNU32-NEXT:  [16] only_unknown
+#  GNU32-NEXT:  [15] only_unknown
 #  GNU32-NEXT:       PROGBITS        00000000 000034 000000 00   0   0  0
 #  GNU32-NEXT:       [000f0000]: UNKNOWN (000f0000)
-#  GNU32-NEXT:  [17] .strtab
-#  GNU32-NEXT:       STRTAB          00000000 000034 000001 00   0   0  1
+#  GNU32-NEXT:  [16] compressed_corrupted
+#  GNU32-NEXT:       PROGBITS        00000000 000034 000000 00   0   0  0
+#  GNU32-NEXT:       [00000800]: COMPRESSED
+#  GNU32-NEXT:{{.*}}: warning: '[[FILE]]': SHF_COMPRESSED section 'compressed_corrupted' does not have an Elf_Chdr header
+#  GNU32-NEXT:       [<corrupt>]
+#  GNU32-NEXT:  [17] compressed_zlib
+#  GNU32-NEXT:       PROGBITS        00000000 000034 000017 00   0   0  0
+#  GNU32-NEXT:       [00000800]: COMPRESSED
+#  GNU32-NEXT:       ZLIB, 00000004, 2
+#  GNU32-NEXT:  [18] compressed_zstd
+#  GNU32-NEXT:       PROGBITS        00000000 00004b 00001d 00   0   0  0
+#  GNU32-NEXT:       [00000800]: COMPRESSED
+#  GNU32-NEXT:       ZSTD, 00000004, 2
+#  GNU32-NEXT:  [19] compressed_unknown
+#  GNU32-NEXT:       PROGBITS        00000000 000068 00000c 00   0   0  0
+#  GNU32-NEXT:       [00000800]: COMPRESSED
+#  GNU32-NEXT:       [<unknown>: 0x3], 00000004, 2
+#  GNU32-NEXT:  [20] .strtab
+#  GNU32-NEXT:       STRTAB          00000000 000074 000001 00   0   0  1
 #  GNU32-NEXT:       [00000000]: {{$}}
-#  GNU32-NEXT:  [18] .shstrtab
-#  GNU32-NEXT:       STRTAB          00000000 000035 0000b0 00   0   0  1
+#  GNU32-NEXT:  [21] .shstrtab
+#  GNU32-NEXT:       STRTAB          00000000 000075 0000ed 00   0   0  1
 #  GNU32-NEXT:       [00000000]: {{$}}
 #  GNU32-NOT:{{.}}
 
 ## When --section-details and --sections are both specified, --sections is ignored.
-# RUN: llvm-readelf %t64.o --section-details --sections | FileCheck %s --check-prefix=GNU64
-# RUN: llvm-readelf %t64.o --sections --section-details | FileCheck %s --check-prefix=GNU64
+# RUN: llvm-readelf %t64.o --section-details --sections 2>&1 | FileCheck %s -DFILE=%t64.o --check-prefix=GNU64
+# RUN: llvm-readelf %t64.o --sections --section-details 2>&1 | FileCheck %s -DFILE=%t64.o --check-prefix=GNU64
 
 ## Check that we produce the same output with -t (alias).
 # RUN: llvm-readelf --section-details %t64.o > %t.readelf.full
 # RUN: llvm-readelf -t %t64.o > %t.readelf.alias
 # RUN: cmp %t.readelf.full %t.readelf.alias
 
 ## Check how we dump sections when the section header string table can't be read.
 

llvm/tools/llvm-readobj/ELFDumper.cpp

for (const Elf_Shdr &S : Sections) {
     };
 
     PrintUnknownFlags(SHF_MASKOS, "OS");
     PrintUnknownFlags(SHF_MASKPROC, "PROC");
     PrintUnknownFlags(uint64_t(-1), "UNKNOWN");
 
     OS << "\n";
     ++SectionIndex;
+
+    if (!(S.sh_flags & SHF_COMPRESSED))
+      continue;
+    Expected<ArrayRef<uint8_t>> Data = this->Obj.getSectionContents(S);
+    if (!Data || Data->size() < sizeof(Elf_Chdr)) {
+      consumeError(Data.takeError());
+      reportWarning(createError("SHF_COMPRESSED section '" + Name +
+                                "' does not have an Elf_Chdr header"),
+                    this->FileName);
+      OS.indent(7);
+      OS << "[<corrupt>]";
+    } else {
+      OS.indent(7);
+      auto *Chdr = reinterpret_cast<const Elf_Chdr *>(Data->data());
+      if (Chdr->ch_type == ELFCOMPRESS_ZLIB)
+        OS << "ZLIB";
+      else if (Chdr->ch_type == ELFCOMPRESS_ZSTD)
+        OS << "ZSTD";
+      else
+        OS << format("[<unknown>: 0x%x]", unsigned(Chdr->ch_type));
+      OS << ", " << format_hex_no_prefix(Chdr->ch_size, ELFT::Is64Bits ? 16 : 8)
+         << ", " << Chdr->ch_addralign;
+    }
+    OS << '\n';
   }
 }
 
 static inline std::string printPhdrFlags(unsigned Flag) {
   std::string Str;
   Str = (Flag & PF_R) ? "R" : " ";
   Str += (Flag & PF_W) ? "W" : " ";
   Str += (Flag & PF_X) ? "E" : " ";