[llvm-objcopy][ELF] Avoid reordering section headers

As for now, llvm-objcopy sorts section headers according to the offsets
of the sections in the input file. That can corrupt section references
in the dynamic symbol table because it is a loadable section and as such
is not updated by the tool. Even though the section references are not
required for loading the binary correctly, they are still handy for a
user who analyzes the file.

While the patch removes global reordering of section headers, it layouts
the sections in the same way as before, i.e. according to their original
offsets. All that helps the output file to resemble the input better.

Note that the patch removes sorting SHT_GROUP sections to the start of
the list, which was introduced in D62620 in order to ensure that they
come before the group members, along with the corresponding test. The
original issue was caused by the sorting of section headers, so dropping
the sorting also resolves the issue.

Differential Revision: https://reviews.llvm.org/D107653

Author: igorkudrin

llvm/test/tools/llvm-objcopy/ELF/drawf-fission.test renamed to llvm/test/tools/llvm-objcopy/ELF/dwarf-fission.test

@@ -8,36 +8,36 @@
 
 #DWARF:     SectionHeaderCount: 8
 
+#DWARF:     Name: .strtab
 #DWARF:     Name: .debug_loc.dwo
 #DWARF:     Name: .debug_str.dwo
 #DWARF:     Name: .debug_str_offsets.dwo
 #DWARF:     Name: .debug_info.dwo
 #DWARF:     Name: .debug_abbrev.dwo
 #DWARF:     Name: .debug_line.dwo
-#DWARF:     Name: .strtab
 
 #STRIP:     SectionHeaderCount: 24
 
+#STRIP:    Name: .strtab
 #STRIP:    Name: .text
+#STRIP:    Name: .rela.text
 #STRIP:    Name: .rodata.str1.1
 #STRIP:    Name: .debug_str
 #STRIP:    Name: .debug_abbrev
 #STRIP:    Name: .debug_info
+#STRIP:    Name: .rela.debug_info
 #STRIP:    Name: .debug_ranges
 #STRIP:    Name: .debug_macinfo
 #STRIP:    Name: .debug_addr
+#STRIP:    Name: .rela.debug_addr
 #STRIP:    Name: .debug_pubnames
+#STRIP:    Name: .rela.debug_pubnames
 #STRIP:    Name: .debug_pubtypes
+#STRIP:    Name: .rela.debug_pubtypes
 #STRIP:    Name: .comment
 #STRIP:    Name: .note.GNU-stack
 #STRIP:    Name: .debug_frame
-#STRIP:    Name: .debug_line
-#STRIP:    Name: .symtab
-#STRIP:    Name: .rela.text
-#STRIP:    Name: .rela.debug_info
-#STRIP:    Name: .rela.debug_addr
-#STRIP:    Name: .rela.debug_pubnames
-#STRIP:    Name: .rela.debug_pubtypes
 #STRIP:    Name: .rela.debug_frame
+#STRIP:    Name: .debug_line
 #STRIP:    Name: .rela.debug_line
-#STRIP:    Name: .strtab
+#STRIP:    Name: .symtab

llvm/test/tools/llvm-objcopy/ELF/dynsym-valid-refs.test

@@ -0,0 +1,69 @@
+# RUN: yaml2obj %s -o %t
+# RUN: llvm-objcopy %t %t2
+# RUN: llvm-readobj --dyn-syms %t2 | FileCheck %s
+
+## This checks that section references in the dynamic symbol table are not
+## corrupted after processing a file where the sequence of section headers does
+## not follow the order of their offsets. The tool avoids updating loadable
+## sections, so, the content of the dynamic symbol table stays intact and the
+## used section indices are preserved. In this test, the section 'dummy' comes
+## first while having the offset after all other sections. If the section
+## headers were sorted by their offsets by the tool, what it did before, the
+## index of the '.text' section would change from '2' to '1', which resulted
+## in an incorrect reference in the corresponding dynamic symbol 'foo'.
+
+# CHECK:      Name: foo
+# CHECK-NEXT: Value:
+# CHECK-NEXT: Size:
+# CHECK-NEXT: Binding:
+# CHECK-NEXT: Type:
+# CHECK-NEXT: Other:
+# CHECK-NEXT: Section: .text
+
+!ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_DYN
+  Machine:         EM_X86_64
+ProgramHeaders:
+  - Type:            PT_LOAD
+    Flags:           [ PF_X, PF_R ]
+    FirstSec:        .text
+    LastSec:         .text
+    Align:           0x1000
+Sections:
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    AddressAlign:    0x4
+    Offset:          0x1000
+    Content:         0000000000000000
+  - Name:            .dynsym
+    Type:            SHT_DYNSYM
+    Flags:           [ SHF_ALLOC ]
+    Link:            .dynstr
+  - Name:            .dynstr
+    Type:            SHT_STRTAB
+    Flags:           [ SHF_ALLOC ]
+  - Name:            dummy
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC ]
+    Offset:          0x1100
+  - Type:            SectionHeaderTable
+    Sections:
+## 'dummy' comes before '.text' in the section header table despite its offset
+## is larger.
+      - Name:            dummy
+      - Name:            .text
+      - Name:            .dynsym
+      - Name:            .dynstr
+      - Name:            .shstrtab
+      - Name:            .strtab
+DynamicSymbols:
+  - Name:            foo
+    Type:            STT_FUNC
+    Section:         .text
+    Binding:         STB_GLOBAL
+    Value:           0x0
+    Size:            0x8

llvm/test/tools/llvm-objcopy/ELF/group-reorder.test

@@ -4,66 +4,62 @@
 # RUN: llvm-objcopy -I ihex -O elf32-i386 %t.hex %t2
 # RUN: llvm-readobj --section-headers %t2 | FileCheck %s
 
-# CHECK:         Index: 1
-# CHECK-NEXT:    Name: .sec1
+# CHECK:         Name: .sec1
 # CHECK-NEXT:    Type: SHT_PROGBITS (0x1)
 # CHECK-NEXT:    Flags [ (0x3)
 # CHECK-NEXT:      SHF_ALLOC (0x2)
 # CHECK-NEXT:      SHF_WRITE (0x1)
 # CHECK-NEXT:    ]
 # CHECK-NEXT:    Address: 0x0
-# CHECK-NEXT:    Offset: 0x34
+# CHECK-NEXT:    Offset:
 # CHECK-NEXT:    Size: 21
 # CHECK-NEXT:    Link: 0
 # CHECK-NEXT:    Info: 0
 # CHECK-NEXT:    AddressAlignment: 1
 # CHECK-NEXT:    EntrySize: 0
 
-# CHECK:         Index: 2
-# CHECK-NEXT:    Name: .sec2
+# CHECK:         Name: .sec2
 # CHECK-NEXT:    Type: SHT_PROGBITS (0x1)
 # CHECK-NEXT:    Flags [ (0x3)
 # CHECK-NEXT:      SHF_ALLOC (0x2)
 # CHECK-NEXT:      SHF_WRITE (0x1)
 # CHECK-NEXT:    ]
 # CHECK-NEXT:    Address: 0xFFF8
-# CHECK-NEXT:    Offset: 0x49
+# CHECK-NEXT:    Offset:
 # CHECK-NEXT:    Size: 11
 # CHECK-NEXT:    Link: 0
 # CHECK-NEXT:    Info: 0
 # CHECK-NEXT:    AddressAlignment: 1
 # CHECK-NEXT:    EntrySize: 0
 
-# CHECK:         Index: 3
-# CHECK-NEXT:    Name: .sec3
+# CHECK:         Name: .sec3
 # CHECK-NEXT:    Type: SHT_PROGBITS (0x1)
 # CHECK-NEXT:    Flags [ (0x3)
 # CHECK-NEXT:      SHF_ALLOC (0x2)
 # CHECK-NEXT:      SHF_WRITE (0x1)
 # CHECK-NEXT:    ]
 # CHECK-NEXT:    Address: 0x10100
-# CHECK-NEXT:    Offset: 0x54
+# CHECK-NEXT:    Offset:
 # CHECK-NEXT:    Size: 4
 # CHECK-NEXT:    Link: 0
 # CHECK-NEXT:    Info: 0
 # CHECK-NEXT:    AddressAlignment: 1
 # CHECK-NEXT:    EntrySize: 0
 
-# CHECK:         Index: 4
-# CHECK-NEXT:    Name: .sec4
+# CHECK:         Name: .sec4
 # CHECK-NEXT:    Type: SHT_PROGBITS (0x1)
 # CHECK-NEXT:    Flags [ (0x3)
 # CHECK-NEXT:      SHF_ALLOC (0x2)
 # CHECK-NEXT:      SHF_WRITE (0x1)
 # CHECK-NEXT:    ]
 # CHECK-NEXT:    Address: 0x10FFF8
-# CHECK-NEXT:    Offset: 0x58
+# CHECK-NEXT:    Offset:
 # CHECK-NEXT:    Size: 11
 # CHECK-NEXT:    Link: 0
 # CHECK-NEXT:    Info: 0
 # CHECK-NEXT:    AddressAlignment: 1
 # CHECK-NEXT:    EntrySize: 0
-  
+
 ## Check section contents.
 # RUN: llvm-objcopy -O binary --only-section=.text %t %t.text
 # RUN: llvm-objcopy -O binary --only-section=.sec1 %t2 %t2.sec1
@@ -82,37 +78,34 @@
 # RUN: llvm-objcopy -I ihex -O elf32-i386 %p/Inputs/sections.hex %t-raw
 # RUN: llvm-readobj --section-headers %t-raw | FileCheck %s --check-prefix=RAW
 
-# RAW:          Index: 1
-# RAW-NEXT:     Name: .sec1
+# RAW:          Name: .sec1
 # RAW-NEXT:     Type: SHT_PROGBITS (0x1)
 # RAW-NEXT:     Flags [ (0x3)
 # RAW-NEXT:       SHF_ALLOC (0x2)
 # RAW-NEXT:       SHF_WRITE (0x1)
 # RAW-NEXT:     ]
 # RAW-NEXT:     Address: 0x1FFF8
-# RAW-NEXT:     Offset: 0x34
+# RAW-NEXT:     Offset:
 # RAW-NEXT:     Size: 11
 
-# RAW:          Index: 2
-# RAW-NEXT:     Name: .sec2
+# RAW:          Name: .sec2
 # RAW-NEXT:     Type: SHT_PROGBITS (0x1)
 # RAW-NEXT:     Flags [ (0x3)
 # RAW-NEXT:       SHF_ALLOC (0x2)
 # RAW-NEXT:       SHF_WRITE (0x1)
 # RAW-NEXT:     ]
 # RAW-NEXT:     Address: 0xFFFF8
-# RAW-NEXT:     Offset: 0x3F
+# RAW-NEXT:     Offset:
 # RAW-NEXT:     Size: 11
 
-# RAW:          Index: 3
-# RAW-NEXT:     Name: .sec3
+# RAW:          Name: .sec3
 # RAW-NEXT:     Type: SHT_PROGBITS (0x1)
 # RAW-NEXT:     Flags [ (0x3)
 # RAW-NEXT:       SHF_ALLOC (0x2)
 # RAW-NEXT:       SHF_WRITE (0x1)
 # RAW-NEXT:     ]
 # RAW-NEXT:     Address: 0x1FFFF8
-# RAW-NEXT:     Offset: 0x4A
+# RAW-NEXT:     Offset:
 # RAW-NEXT:     Size: 11
 
 ## Check section contents.

llvm/test/tools/llvm-objcopy/ELF/ihex-reader.test

@@ -0,0 +1,65 @@
+# RUN: yaml2obj %s -o %t
+# RUN: llvm-objcopy %t %t2
+# RUN: llvm-readobj --sections %t2 | FileCheck %s
+
+## This checks that llvm-objcopy layouts sections in the order of their offsets
+## in the input file in spite of the order of section headers is different.
+
+# CHECK:      Index: 1
+# CHECK-NEXT: Name: foo
+# CHECK-NEXT: Type:
+# CHECK-NEXT: Flags [
+# CHECK-NEXT:   SHF_ALLOC
+# CHECK-NEXT: ]
+# CHECK-NEXT: Address:
+# CHECK-NEXT: Offset: 0x50
+# CHECK:      Index: 2
+# CHECK-NEXT: Name: bar
+# CHECK-NEXT: Type: SHT_PROGBITS
+# CHECK-NEXT: Flags [
+# CHECK-NEXT:   SHF_ALLOC
+# CHECK-NEXT: ]
+# CHECK-NEXT: Address:
+# CHECK-NEXT: Offset: 0x40
+# CHECK:      Index: 3
+# CHECK-NEXT: Name: baz
+# CHECK-NEXT: Type: SHT_PROGBITS
+# CHECK-NEXT: Flags [
+# CHECK-NEXT:   SHF_ALLOC
+# CHECK-NEXT: ]
+# CHECK-NEXT: Address:
+# CHECK-NEXT: Offset: 0x48
+
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_REL
+  Machine:         EM_X86_64
+Sections:
+  - Name:            bar
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC ]
+    AddressAlign:    0x4
+    Offset:          0x40
+    Content:         0000000000000000
+  - Name:            baz
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC ]
+    AddressAlign:    0x4
+    Offset:          0x48
+    Content:         0000000000000000
+  - Name:            foo
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC ]
+    AddressAlign:    0x4
+    Offset:          0x50
+    Content:         0000000000000000
+  - Type:            SectionHeaderTable
+    Sections:
+## Note: the order of section headers differs from their layout.
+      - Name:            foo
+      - Name:            bar
+      - Name:            baz
+      - Name:            .shstrtab
+      - Name:            .strtab