Bug 19392 - Second PT_LOAD starts before the first section in some cases
Summary: Second PT_LOAD starts before the first section in some cases
Status: NEW
Alias: None
Product: binutils
Classification: Unclassified
Component: gold (show other bugs)
Version: unspecified
: P2 normal
Target Milestone: ---
Assignee: Cary Coutant
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2015-12-22 00:21 UTC by Mike Hommey
Modified: 2015-12-31 10:52 UTC (History)
1 user (show)

See Also:
Host:
Target:
Build:
Last reconfirmed:


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Description Mike Hommey 2015-12-22 00:21:39 UTC
$ gold --version
GNU gold (GNU Binutils for Debian 2.25.90.20151209) 1.11
Copyright (C) 2015 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or (at your option) a later version.
This program has absolutely no warranty.

$ cat > test.c <<EOF
void foo() {}
EOF
$ gcc -shared -o test.so test.c -fuse-ld=gold -nostartfiles
$ readelf -Sl test.so
There are 16 section headers, starting at offset 0x598:

Section Headers:
  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  [ 0]                   NULL             0000000000000000  00000000
       0000000000000000  0000000000000000           0     0     0
  [ 1] .note.gnu.build-i NOTE             00000000000001c8  000001c8
       0000000000000024  0000000000000000   A       0     0     4
  [ 2] .dynsym           DYNSYM           00000000000001f0  000001f0
       0000000000000078  0000000000000018   A       3     1     8
  [ 3] .dynstr           STRTAB           0000000000000268  00000268
       0000000000000027  0000000000000000   A       0     0     1
  [ 4] .gnu.hash         GNU_HASH         0000000000000290  00000290
       0000000000000034  0000000000000000   A       2     0     8
  [ 5] .text             PROGBITS         00000000000002c4  000002c4
       0000000000000007  0000000000000000  AX       0     0     1
  [ 6] .eh_frame         PROGBITS         00000000000002d0  000002d0
       0000000000000038  0000000000000000   A       0     0     8
  [ 7] .eh_frame_hdr     PROGBITS         0000000000000308  00000308
       0000000000000014  0000000000000000   A       0     0     4
  [ 8] .dynamic          DYNAMIC          0000000000001320  00000320
       00000000000000c0  0000000000000010  WA       3     0     8
  [ 9] .data             PROGBITS         00000000000013e0  000003e0
       0000000000000000  0000000000000000  WA       0     0     1
  [10] .bss              NOBITS           00000000000013e0  000003e0
       0000000000000000  0000000000000000  WA       0     0     1
  [11] .comment          PROGBITS         0000000000000000  000003e0
       0000000000000027  0000000000000001  MS       0     0     1
  [12] .note.gnu.gold-ve NOTE             0000000000000000  00000408
       000000000000001c  0000000000000000           0     0     4
  [13] .symtab           SYMTAB           0000000000000000  00000428
       00000000000000a8  0000000000000018          14     3     8
  [14] .strtab           STRTAB           0000000000000000  000004d0
       000000000000002d  0000000000000000           0     0     1
  [15] .shstrtab         STRTAB           0000000000000000  000004fd
       000000000000009a  0000000000000000           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)

Elf file type is DYN (Shared object file)
Entry point 0x0
There are 7 program headers, starting at offset 64

Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  PHDR           0x0000000000000040 0x0000000000000040 0x0000000000000040
                 0x0000000000000188 0x0000000000000188  R      8
  LOAD           0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x000000000000031c 0x000000000000031c  R E    1000
  LOAD           0x000000000000031c 0x000000000000131c 0x000000000000131c
                 0x00000000000000c4 0x00000000000000c4  RW     1000
  DYNAMIC        0x0000000000000320 0x0000000000001320 0x0000000000001320
                 0x00000000000000c0 0x00000000000000c0  RW     8
  NOTE           0x00000000000001c8 0x00000000000001c8 0x00000000000001c8
                 0x0000000000000024 0x0000000000000024  R      4
  GNU_EH_FRAME   0x0000000000000308 0x0000000000000308 0x0000000000000308
                 0x0000000000000014 0x0000000000000014  R      4
  GNU_STACK      0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000  RW     0

 Section to Segment mapping:
  Segment Sections...
   00     
   01     .note.gnu.build-id .dynsym .dynstr .gnu.hash .text .eh_frame .eh_frame_hdr 
   02     .dynamic 
   03     .dynamic 
   04     .note.gnu.build-id 
   05     .eh_frame_hdr 
   06    

The relevant parts are that the second PT_LOAD starts at 0x31c and contains .dynamic, which starts at 0x320. It fortunately compensates on the size to end at the right address.
Comment 1 Mike Hommey 2015-12-31 10:52:35 UTC
Bisected:

a5cd8f05ca759fdb9b27fc98a08edb5f85369ad9 is the first bad commit
commit a5cd8f05ca759fdb9b27fc98a08edb5f85369ad9
Author: Cary Coutant <ccoutant@google.com>
Date:   Fri Jan 9 15:55:50 2015 -0800

    Don't align start of segment unless alignment is larger than page size.
    
    This fixes an issue where a page-aligned data section, combined with -z relro,
    could lead to a gap between text and data segments larger than a page, and
    we would fail to overlap the segments in the file.
    
    gold/
    	* layout.cc (Layout::set_segment_offsets): Don't align start of segment
    	unless alignment is larger than page size.

:040000 040000 a0187d8ed6745a9d727f8b342e79a9c57216a93e 93e6a9db741fc3ec9bd7cb4f22199bd4e9af672c M	gold