[klibc] klibc loader crash...

[Paweł Sikora]

Dnia środa, 12 października 2005 21:07, H. Peter Anvin napisał:
> Paweł Sikora wrote:
> > Hi,
> >
> > This is not a klibc bug. It is a kernel issue.
> >
> > Fixed in 2.6.14rc4-git1: [PATCH] binfmt_elf bss padding fix
> >
> >  Nir Tzachar <tzachar at cs.bgu.ac.il> points out that if an ELF file
> > specifies a zero-length bss at a whacky address, we cannot load that
> > binary because padzero() tries to zero out the end of the page at the
> > whacky address, and that may not be writeable.
> >
> >  See also http://bugzilla.kernel.org/show_bug.cgi?id=5411
> >
> >  So teach load_elf_binary() to skip the bss settng altogether if the elf
> > file has a zero-length bss segment.
>
> Hm.  This still confuses me.
>
> __libc_init() should always allocate three pointer values, so .bss
> should never be empty with klibc-generated code.c.  utils/true.c looks
> like the following:
>
> int main(void)
> {
>    return 0;
> }
>
> ... and it generates the following headers when compiled for i386:
>
> Sections:
> Idx Name          Size      VMA       LMA       File off  Algn
>    0 .text         00000070  08048094  08048094  00000094  2**2
>                    CONTENTS, ALLOC, LOAD, READONLY, CODE
>    1 .data         00000004  08049104  08049104  00000104  2**2
>                    CONTENTS, ALLOC, LOAD, DATA
>    2 .bss          0000000c  08049108  08049108  00000108  2**2
>                    ALLOC
>
>   Section to Segment mapping:
>    Segment Sections...
>     00     .text
>     01     .data .bss
>     02

This is true only for statically linked klibc.
With shared version we get:

Sections:
Idx Name          Size      VMA       LMA       File off  Algn
  0 .interp       0000000e  080480f4  080480f4  000000f4  2**0
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  1 .text         00000003  08048110  08048110  00000110  2**4
                  CONTENTS, ALLOC, LOAD, READONLY, CODE

Program Headers:
  Type           Offset   VirtAddr   PhysAddr   FileSiz  MemSiz   Flg Align
  PHDR           0x000034 0x08048034 0x08048034 0x0000a0 0x0000a0 R E 0x4
  INTERP         0x0000f4 0x080480f4 0x080480f4 0x00000e 0x00000e R   0x1
        [Requesting program interpreter: /lib/klibc.so]
  LOAD           0x000000 0x08048000 0x08048000 0x000113 0x000113 R E 0x1000
  GNU_STACK      0x000000 0x00000000 0x00000000 0x000000 0x000000 RWE 0x4
  LOOS+84153728  0x000000 0x00000000 0x00000000 0x000000 0x000000     0x4

 Section to Segment mapping:
  Segment Sections...
   00
   01      [RO: .interp]
   02      [RO: .interp .text]
   03
   04

$ ld --version
GNU ld version 2.16.91.0.3 20050821

-- 
The only thing necessary for the triumph of evil
  is for good men to do nothing.
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