[PATCH] D42872: Fix handling of zero-size segments in llvm-objcopy

[vit9696 via Phabricator via llvm-commits]

vit9696 created this revision.
vit9696 added a reviewer: jakehehrlich.
Herald added subscribers: llvm-commits, kristof.beyls, aemerson.

Some ELF files produced by lld may have zero-size segment placeholders as shown below.
Since GNU_STACK Offset is 0, the current code makes it the lowest used offset, and relocates all the segments over the ELF header. The resulting binary is total garbage.

  Program Headers:
    Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
    LOAD           0x001000 0xc0000000 0x10000000 0x48000 0x48000 R E 0x1000
    LOAD           0x04c000 0xc0048000 0x10048000 0x155e0 0x67000 RW  0x4000
    GNU_STACK      0x000000 0x00000000 0x00000000 0x00000 0x00000 RW  0x0
  
  Section Headers:
    [Nr] Name              Type            Address  Off    Size   ES Flg Lk Inf Al
    [ 0]                   NULL            00000000 000000 000000 00      0   0  0
    [ 1] .text             PROGBITS        c0000000 001000 01e7d4 00  AX  0   0  4
    [ 2] .vector_table     PROGBITS        c001e7d4 01f7d4 000038 00   A  0   0  4
    [ 3] .rodata           PROGBITS        c001e80c 01f80c 0297f4 00 AMS  0   0  4
    [ 4] .data             PROGBITS        c0048000 04c000 0155e0 00  WA  0   0 16384
    [ 5] .bss              NOBITS          c0060000 0615e0 04f000 00  WA  0   0 16384
    [ 6] .ARM.attributes   ARM_ATTRIBUTES  00000000 0615e0 00002f 00      0   0  1
    [ 7] .debug_line       PROGBITS        00000000 06160f 015219 00      0   0  1
    [ 8] .debug_info       PROGBITS        00000000 076828 01e940 00      0   0  1
    [ 9] .debug_abbrev     PROGBITS        00000000 095168 00435f 00      0   0  1
    [10] .debug_aranges    PROGBITS        00000000 0994c7 0000e8 00      0   0  1
    [11] .debug_str        PROGBITS        00000000 0995af 008095 01  MS  0   0  1
    [12] .debug_ranges     PROGBITS        00000000 0a1644 0000a0 00      0   0  1
    [13] .debug_macinfo    PROGBITS        00000000 0a16e4 00003a 00      0   0  1
    [14] .debug_pubnames   PROGBITS        00000000 0a171e 004fc6 00      0   0  1
    [15] .debug_pubtypes   PROGBITS        00000000 0a66e4 007099 00      0   0  1
    [16] .comment          PROGBITS        00000000 0ad77d 000045 01  MS  0   0  1
    [17] .debug_frame      PROGBITS        00000000 0ad7c4 004740 00      0   0  4
    [18] .debug_loc        PROGBITS        00000000 0b1f04 000522 00      0   0  1
    [19] .symtab           SYMTAB          00000000 0b2428 003a50 10     21 469  4
    [20] .shstrtab         STRTAB          00000000 0b5e78 0000f0 00      0   0  1
    [21] .strtab           STRTAB          00000000 0b5f68 004252 00      0   0  1
  Key to Flags:
    W (write), A (alloc), X (execute), M (merge), S (strings), l (large)
    I (info), L (link order), G (group), T (TLS), E (exclude), x (unknown)
    O (extra OS processing required) o (OS specific), p (processor specific)


Repository:
  rL LLVM

https://reviews.llvm.org/D42872

Files:
  tools/llvm-objcopy/Object.cpp


Index: tools/llvm-objcopy/Object.cpp
===================================================================
--- tools/llvm-objcopy/Object.cpp
+++ tools/llvm-objcopy/Object.cpp
@@ -911,8 +911,10 @@
   // so that we know that anytime ->ParentSegment is set that segment has
   // already had its offset properly set.
   std::vector<Segment *> OrderedSegments;
-  for (auto &Segment : Obj.segments())
-    OrderedSegments.push_back(&Segment);
+  for (auto &Segment : Obj.segments()) {
+    if (Segment.FileSize > 0)
+      OrderedSegments.push_back(&Segment);
+  }
   OrderSegments(OrderedSegments);
   // The size of ELF + program headers will not change so it is ok to assume
   // that the first offset of the first segment is a good place to start


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