[llvm] 1c57752 - [obj2yaml] - Teach obj2yaml to dump SHT_NOBITS sections when dumping program headers.

[Georgii Rymar via llvm-commits]

Author: Georgii Rymar
Date: 2020-04-20T14:35:28+03:00
New Revision: 1c57752ff5e2e5effcedc5da097c4109696f44bb

URL: https://github.com/llvm/llvm-project/commit/1c57752ff5e2e5effcedc5da097c4109696f44bb
DIFF: https://github.com/llvm/llvm-project/commit/1c57752ff5e2e5effcedc5da097c4109696f44bb.diff

LOG: [obj2yaml] - Teach obj2yaml to dump SHT_NOBITS sections when dumping program headers.

SHT_NOBITS are a bit special because occupy no physical space.
This patch adds support for them.

Differential revision: https://reviews.llvm.org/D77805

Added: 
    

Modified: 
    llvm/test/tools/obj2yaml/program-headers.yaml
    llvm/tools/obj2yaml/elf2yaml.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/test/tools/obj2yaml/program-headers.yaml b/llvm/test/tools/obj2yaml/program-headers.yaml
index 7f31494bd20e..22b86865a90e 100644
--- a/llvm/test/tools/obj2yaml/program-headers.yaml
+++ b/llvm/test/tools/obj2yaml/program-headers.yaml
@@ -414,3 +414,106 @@ Sections:
     Type:    SHT_PROGBITS
     Flags:   [ SHF_ALLOC ]
     Size:    0x1
+
+## Check how we dump segments which contain SHT_NOBITS sections.
+# RUN: yaml2obj --docnum=5 %s -o %t5
+# RUN: obj2yaml %t5 | FileCheck %s --check-prefix=NOBITS
+
+# NOBITS:      ProgramHeaders:
+# NOBITS-NEXT:   - Type:  PT_LOAD
+# NOBITS-NEXT:     Flags: [ PF_W, PF_R ]
+# NOBITS-NEXT:     Sections:
+# NOBITS-NEXT:       - Section: .bss
+# NOBITS-NEXT:   - Type:  PT_LOAD
+# NOBITS-NEXT:     Flags: [ PF_W, PF_R ]
+# NOBITS-NEXT:     Sections:
+# NOBITS-NEXT:       - Section: .data.1
+# NOBITS-NEXT:       - Section: .bss
+# NOBITS-NEXT:   - Type:  PT_LOAD
+# NOBITS-NEXT:     Flags: [ PF_W, PF_R ]
+# NOBITS-NEXT:     Sections:
+# NOBITS-NEXT:       - Section: .data.1
+# NOBITS-NEXT:       - Section: .bss
+# NOBITS-NEXT:       - Section: .data.2
+# NOBITS-NEXT:   - Type:  PT_LOAD
+# NOBITS-NEXT:     Flags: [ PF_W, PF_R ]
+# NOBITS-NEXT:     Sections:
+# NOBITS-NEXT:       - Section: .bss
+# NOBITS-NEXT:       - Section: .data.2
+# NOBITS-NEXT:   - Type:  PT_LOAD
+# NOBITS-NEXT:     Flags: [ PF_W, PF_R ]
+# NOBITS-NEXT:     Sections:
+# NOBITS-NEXT:       - Section: .foo.bss
+# NOBITS-NEXT:       - Section: .bar.bss
+# NOBITS-NEXT:     VAddr: 0x0000000200000000
+# NOBITS-NEXT: Sections:
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_EXEC
+  Machine: EM_X86_64
+ProgramHeaders:
+## Case 1: the segment contains a single SHT_NOBITS section.
+  - Type:  PT_LOAD
+    Flags: [ PF_W, PF_R ]
+    Sections:
+      - Section: .bss
+## Case 2: the SHT_NOBITS section is the last section in the segment.
+  - Type:  PT_LOAD
+    Flags: [ PF_W, PF_R ]
+    Sections:
+      - Section: .data.1
+      - Section: .bss
+## Case 3: the SHT_NOBITS section is in the middle of the segment.
+  - Type:  PT_LOAD
+    Flags: [ PF_W, PF_R ]
+    Sections:
+      - Section: .data.1
+      - Section: .bss
+      - Section: .data.2
+## Case 4: the SHT_NOBITS section is the first section in the segment.
+  - Type:  PT_LOAD
+    Flags: [ PF_W, PF_R ]
+    Sections:
+      - Section: .bss
+      - Section: .data.2
+## Case 5: another two SHT_NOBITS sections in a 
diff erent segment.
+  - Type:  PT_LOAD
+    Flags: [ PF_W, PF_R ]
+    Sections:
+      - Section: .foo.bss
+      - Section: .bar.bss
+    VAddr: 0x200000000
+Sections:
+  - Name:    .data.1
+    Type:    SHT_PROGBITS
+    Flags:   [ SHF_WRITE, SHF_ALLOC ]
+## Use an arbitrary address and size.
+    Address: 0x1000
+    Size:    0x1
+  - Name:  .bss
+    Type:  SHT_NOBITS
+    Flags: [ SHF_WRITE, SHF_ALLOC ]
+## Use a size that is larger than the file size.
+    Size:  0x00000000FFFFFFFF
+  - Name:  .data.2
+    Type:  SHT_PROGBITS
+    Flags: [ SHF_WRITE, SHF_ALLOC ]
+## Use an arbitrary size.
+    Size:  0x1
+  - Name:    .foo.bss
+    Type:    SHT_NOBITS
+    Flags:   [ SHF_WRITE, SHF_ALLOC ]
+## Set an arbitrary address and size so that this section can be used
+## to start a 
diff erent non-overlapping segment.
+## I.e. its address is larger than addresses of previous sections.
+    Size:    0x10
+    Address: 0x200000000
+  - Name:    .bar.bss
+    Type:    SHT_NOBITS
+    Flags:   [ SHF_WRITE, SHF_ALLOC ]
+## Use an arbitrary size that is 
diff erent to the size of
+## the previous section.
+    Size:    0x20

diff  --git a/llvm/tools/obj2yaml/elf2yaml.cpp b/llvm/tools/obj2yaml/elf2yaml.cpp
index ac0d1e9e1ba7..c145142f65bc 100644
--- a/llvm/tools/obj2yaml/elf2yaml.cpp
+++ b/llvm/tools/obj2yaml/elf2yaml.cpp
@@ -298,8 +298,24 @@ static bool isInSegment(const ELFYAML::Section &Sec,
                         const typename ELFT::Phdr &Phdr) {
   if (Sec.Type == ELF::SHT_NULL)
     return false;
-  return SHdr.sh_offset >= Phdr.p_offset &&
-         (SHdr.sh_offset + SHdr.sh_size <= Phdr.p_offset + Phdr.p_filesz);
+
+  // A section is within a segment when its location in a file is within the
+  // [p_offset, p_offset + p_filesz] region.
+  bool FileOffsetsMatch =
+      SHdr.sh_offset >= Phdr.p_offset &&
+      (SHdr.sh_offset + SHdr.sh_size <= Phdr.p_offset + Phdr.p_filesz);
+
+  if (FileOffsetsMatch)
+    return true;
+
+  // SHT_NOBITS sections usually occupy no physical space in a file. Such
+  // sections belong to a segment when they reside in the segment's virtual
+  // address space.
+  if (Sec.Type != ELF::SHT_NOBITS)
+    return false;
+
+  return SHdr.sh_addr >= Phdr.p_vaddr &&
+         SHdr.sh_addr <= Phdr.p_vaddr + Phdr.p_memsz;
 }
 
 template <class ELFT>