Re:Re: What is the memory region ?

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 




Thanks Prabhunath!

The following is section header table:
==============================
 readelf -S /bin/cat

There are 28 section headers, starting at offset 0xb260:

Section Headers:
  [Nr] Name              Type            Addr     Off    Size   ES Flg Lk Inf Al
  [ 0]                   NULL            00000000 000000 000000 00      0   0  0
  [ 1] .interp           PROGBITS        08048154 000154 000013 00   A  0   0  1
  [ 2] .note.ABI-tag     NOTE            08048168 000168 000020 00   A  0   0  4
  [ 3] .note.gnu.build-i NOTE            08048188 000188 000024 00   A  0   0  4
  [ 4] .gnu.hash         GNU_HASH        080481ac 0001ac 000044 04   A  5   0  4
  [ 5] .dynsym           DYNSYM          080481f0 0001f0 0004e0 10   A  6   1  4
  [ 6] .dynstr           STRTAB          080486d0 0006d0 000349 00   A  0   0  1
  [ 7] .gnu.version& nbsp;     VERSYM          08048a1a 000a1a 00009c 02   A  5   0  2
  [ 8] .gnu.version_r    VERNEED         08048ab8 000ab8 000090 00   A  6   1  4
  [ 9] .rel.dyn          REL             08048b48 000b48 000030 08   A  5   0  4
  [10] .rel.plt          REL             08048b78 000b78 000228 08   A  5  12  4
  [11] .init             PROGBITS        08048da0 000da0 000024 00  AX  0   0  4
  [12] .plt              PROGBITS        08048dd0 000dd0 000460 04  AX  0   0 16
  [13] .text             PROGBITS        08049230 001230 006f2c 00  AX  0   0 16
  [14] .fini             PROGBITS        0805015c 00815c 000015 00  AX  0   0  4
  [15] .rodata           PROGBITS        08050180 008180 000e86 00   A  0   0 32
  [16] .eh_frame_hdr     PROGBITS        08051008 009008 0002d4 00   A  0   0  4
  [17] .eh_frame        ;  PROGBITS        080512dc 0092dc 000d30 00   A  0   0  4
  [18] .init_array       INIT_ARRAY      08053f04 00af04 000004 00  WA  0   0  4
  [19] .fini_array       FINI_ARRAY      08053f08 00af08 000004 00  WA  0   0  4
  [20] .jcr              PROGBITS        08053f0c 00af0c 000004 00  WA  0   0  4
  [21] .dynamic          DYNAMIC         08053f10 00af10 0000e8 08  WA  6   0  4
  [22] .got              PROGBITS        08053ff8 00aff8 000008 04  WA  0   0  4
  [23] .got.plt          PROGBITS        08054000 00b000 000120 04  WA  0   0  4
  [24] .data             PROGBITS        08054120 00b120 00003c 00  WA  0   0  4
  [25] .bss              NOBITS          08054160 00b15c 0005c4 00  WA  0   0 32
  [26] .gnu_debuglink    PROGBITS        00000000 00b15c 000008 00      0   0  1
  [27] .shstrtab         STRTAB          00000000 00b164 00 00fc 00      0   0  1
Key to Flags:
  W (write), A (alloc), X (execute), M (merge), S (strings)
  I (info), L (link order), G (group), T (TLS), E (exclude), x (unknown)
  O (extra OS processing required) o (OS specific), p (processor specific)
==============================

But, according the kernel elf loader :

linux-3.7.4/fs/binfmt_elf.c:
static int load_elf_binary(...)
{
    ...
    for(i = 0, elf_ppnt = elf_phdata;
        i < loc->elf_ex.e_phnum; i++, elf_ppnt++) {
        ...
        if (elf_ppnt->p_type != PT_LOAD)
            continue;
    ...
}

The kernel elf loader just load PT_LOAD segment, but GNU_RELRO is not PT_LOAD type ?

At 2013-03-07 18:53:46,"Prabhu nath" <gprabhunath@xxxxxxxxx> wrote:
Looks like they have added a new section GNU_RELRO in the later versions. The one you are referring is read-only section. It would be nice if you share the section header table.
Plz see inline

Regards,
Prabhunath G
Linux Trainer
Bangalore


On Thu, Mar 7, 2013 at 3:31 PM, Jacky <jackyclivia@xxxxxxx> wrote:
Dear all,

This is the Program Header for "cat" info:

================================
readelf -l /bin/cat
...
Program Headers:
  Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
  PHDR           0x000034 0x08048034 0x08048034 0x00120 0x00120 R E 0x4
  INTERP         0x000154 0x08048154 0x08048154 0x00013 0x00013 R   0x1
      [Requesting program interpreter: /lib/ld-linux.so.2]
  LOAD           0x000000 0x08048000 0x08048000 0x0a00c 0x0a00c R E 0x1000
  LOAD           0x00af04 0x08053f04 0x08053f04 0x00258 0x00820 RW  0x1000
  DYNAMIC        0x00af10 0x08053f10 0x08053f10 0x000e8 0x000e8 RW  0x4
  NOTE           0x000168 0x08048168 0x08048168 0x00044 0x00044 R   0x4
  GNU_EH_FRAME   0x009008 0x08051008 0x08051008 0x002d4 0x002d4 R   0x4
  GNU_STACK      0x000000 0x00000000 0x00000000 0x00000 0x00000 RW  0x4
  GNU_RELRO      0x00af04 0x08053f04 0x08053f04 0x000fc 0x000fc R   0x1
==============================

So there are just 2 PT_LOAD segments. But why kernel maps 3 memory regions ? The following is the maps output:

Though the second PT_LOAD starts at the file offset  0xaf04, The first fc bytes belong to GNU_RELRO segment (The last entry in the Program Header). If you add af04 +fc you get afff. Looks like they have placed this section advertently in such a way that the actual DATA segment will start at the next virtual address page boundary 0x08054000. Thus the GNU_RELRO section with read-only permissions is placed in the separate virtual address region.
    This is the result of the maps file you see below.
============================
cat /proc/self/maps

08048000-08053000 r-xp 00000000 08:01 261656     /bin/cat
08053000-08054000 r--p 0000a000 08:01 261656     /bin/cat
08054000-08055000 rw-p 0000b000 08:01 261656     /bin/cat
09b58000-09b79000 rw-p 00000000 00:00 0          [heap]
b75bd000-b75be000 rw-p 00000000 00:00 0
b75be000-b7761000 r-xp 00000000 08:01 523958     /lib/i386-linux-gnu/libc-2.15.so
...
==================

The above output, there are 3 memory regions for "/bin/cat", and what is the following segment:

08053000-08054000 r--p 0000a000 08:01 261656     /bin/cat

According the 'cat' program header, there is no "r" segment.


Regards,
Jacky


 









_______________________________________________
Kernelnewbies mailing list
Kernelnewbies@xxxxxxxxxxxxxxxxx
http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies




_______________________________________________
Kernelnewbies mailing list
Kernelnewbies@xxxxxxxxxxxxxxxxx
http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

[Index of Archives]     [Newbies FAQ]     [Linux Kernel Mentors]     [Linux Kernel Development]     [IETF Annouce]     [Git]     [Networking]     [Security]     [Bugtraq]     [Yosemite]     [MIPS Linux]     [ARM Linux]     [Linux RAID]     [Linux SCSI]     [Linux ACPI]
  Powered by Linux