[llvm] r371420 - [yaml2obj] Simplify p_filesz/p_memsz computing

[Fangrui Song via llvm-commits]

Author: maskray
Date: Mon Sep  9 09:45:17 2019
New Revision: 371420

URL: http://llvm.org/viewvc/llvm-project?rev=371420&view=rev
Log:
[yaml2obj] Simplify p_filesz/p_memsz computing

This fixes a bug as well. When "FileSize:" (p_filesz) is specified and
different from the actual value, the following code probably should not
use PHeader.p_filesz:

  if (SHeader->sh_offset == PHeader.p_offset + PHeader.p_filesz)
    PHeader.p_memsz += SHeader->sh_size;

Reviewed By: jhenderson

Differential Revision: https://reviews.llvm.org/D67256

Modified:
    llvm/trunk/lib/ObjectYAML/ELFEmitter.cpp
    llvm/trunk/test/tools/yaml2obj/program-header-size-offset.yaml

Modified: llvm/trunk/lib/ObjectYAML/ELFEmitter.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/ObjectYAML/ELFEmitter.cpp?rev=371420&r1=371419&r2=371420&view=diff
==============================================================================
--- llvm/trunk/lib/ObjectYAML/ELFEmitter.cpp (original)
+++ llvm/trunk/lib/ObjectYAML/ELFEmitter.cpp Mon Sep  9 09:45:17 2019
@@ -627,36 +627,24 @@ void ELFState<ELFT>::setProgramHeaderLay
         PHeader.p_offset = std::min(PHeader.p_offset, SHeader->sh_offset);
     }
 
-    // Find the maximum offset of the end of a section in order to set p_filesz,
-    // if not set explicitly.
-    if (YamlPhdr.FileSize) {
-      PHeader.p_filesz = *YamlPhdr.FileSize;
-    } else {
-      PHeader.p_filesz = 0;
-      for (Elf_Shdr *SHeader : Sections) {
-        uint64_t EndOfSection;
-        if (SHeader->sh_type == llvm::ELF::SHT_NOBITS)
-          EndOfSection = SHeader->sh_offset;
-        else
-          EndOfSection = SHeader->sh_offset + SHeader->sh_size;
-        uint64_t EndOfSegment = PHeader.p_offset + PHeader.p_filesz;
-        EndOfSegment = std::max(EndOfSegment, EndOfSection);
-        PHeader.p_filesz = EndOfSegment - PHeader.p_offset;
-      }
-    }
+    // Find the maximum offset of the end of a section in order to set p_filesz
+    // and p_memsz. When setting p_filesz, trailing SHT_NOBITS sections are not
+    // counted.
+    uint64_t FileOffset = PHeader.p_offset, MemOffset = PHeader.p_offset;
+    for (Elf_Shdr *SHeader : Sections) {
+      uint64_t End = SHeader->sh_offset + SHeader->sh_size;
+      MemOffset = std::max(MemOffset, End);
 
-    // If not set explicitly, find the memory size by adding the size of
-    // sections at the end of the segment. These should be empty (size of zero)
-    // and NOBITS sections.
-    if (YamlPhdr.MemSize) {
-      PHeader.p_memsz = *YamlPhdr.MemSize;
-    } else {
-      PHeader.p_memsz = PHeader.p_filesz;
-      for (Elf_Shdr *SHeader : Sections)
-        if (SHeader->sh_offset == PHeader.p_offset + PHeader.p_filesz)
-          PHeader.p_memsz += SHeader->sh_size;
+      if (SHeader->sh_type != llvm::ELF::SHT_NOBITS)
+        FileOffset = std::max(FileOffset, End);
     }
 
+    // Set the file size and the memory size if not set explicitly.
+    PHeader.p_filesz = YamlPhdr.FileSize ? uint64_t(*YamlPhdr.FileSize)
+                                         : FileOffset - PHeader.p_offset;
+    PHeader.p_memsz = YamlPhdr.MemSize ? uint64_t(*YamlPhdr.MemSize)
+                                       : MemOffset - PHeader.p_offset;
+
     // Set the alignment of the segment to be the same as the maximum alignment
     // of the sections with the same offset so that by default the segment
     // has a valid and sensible alignment.

Modified: llvm/trunk/test/tools/yaml2obj/program-header-size-offset.yaml
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/tools/yaml2obj/program-header-size-offset.yaml?rev=371420&r1=371419&r2=371420&view=diff
==============================================================================
--- llvm/trunk/test/tools/yaml2obj/program-header-size-offset.yaml (original)
+++ llvm/trunk/test/tools/yaml2obj/program-header-size-offset.yaml Mon Sep  9 09:45:17 2019
@@ -11,7 +11,7 @@
 
 # CHECK:    Offset: 0x2000
 # CHECK:    FileSize: 6
-# CHECK:    MemSize: 6
+# CHECK:    MemSize: 4
 
 # CHECK:    Offset: 0x2000
 # CHECK:    FileSize: 4
@@ -28,6 +28,10 @@
 # CHECK:    Offset: 0x3000
 # CHECK:    FileSize: 3
 # CHECK:    MemSize: 2
+
+# CHECK:    Offset: 0x2004
+# CHECK:    FileSize: 4
+# CHECK:    MemSize: 6
 # CHECK: ]
 
 !ELF
@@ -40,14 +44,26 @@ Sections:
   - Name: .text
     Type: SHT_PROGBITS
     Size: 4
+    ShOffset: 0x1000
     AddressAlign: 0x1000
   - Name: .rodata
     Type: SHT_PROGBITS
     Size: 4
+    ShOffset: 0x2000
     AddressAlign: 0x1000
   - Name: .data
     Type: SHT_PROGBITS
+    ShOffset: 0x2004
     Size: 4
+  - Name: .nobits1
+    Type: SHT_NOBITS
+    ShOffset: 0x2008
+    Size: 1
+  - Name: .nobits2
+    Type: SHT_NOBITS
+    # Intentionally set to 0x2009 though the previous section is SHT_NOBITS.
+    ShOffset: 0x2009
+    Size: 1
 ProgramHeaders:
   # Program header with no sections.
   - Type:     0x6abcdef0 # arbitrary type
@@ -83,3 +99,10 @@ ProgramHeaders:
     MemSize:  2
     Sections:
       - Section: .data
+  # Program header with 2 SHT_NOBITS sections.
+  - Type:     0x6abcdef0
+    Offset:   0x2004
+    Sections:
+      - Section: .data
+      - Section: .nobits1
+      - Section: .nobits2