Re: [rfc / remote protocol] ELF segment based qOffsets

[Sergei Poselenov <sposelenov@emcraft.com>]

Hello all,

We've ran into the following problem while running the ppc cross-gdb
with the U-Boot firmware image:

bash# ./gdb u-boot
GNU gdb Red Hat Linux (6.7-1rh)
Copyright (C) 2007 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later 
<http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show 
copying"
and "show warranty" for details.
This GDB was configured as "--host=i686-pc-linux-gnu --target=ppc-linux".
The target architecture is set automatically (currently powerpc:403)
..

warning: Loadable segment ".resetvec" outside of ELF segments

warning: Loadable segment ".bootpg" outside of ELF segments
(gdb)


bash# readelf -lS u-boot
There are 27 section headers, starting at offset 0xc3dc0:

Section Headers:
   [Nr] Name              Type            Addr     Off    Size   ES 
Flg Lk Inf Al
   [ 0]                   NULL            00000000 000000 000000 00 
     0   0  0
   [ 1] .resetvec         PROGBITS        fffffffc 02e208 000004 00 
AX  0   0  1
   [ 2] .bootpg           PROGBITS        fffff000 02d20c 00033c 00 
AX  0   0  1
   [ 3] .text             PROGBITS        fffc0000 0000a0 022f9c 00 
AX  0   0 16
   [ 4] .rodata           PROGBITS        fffe2f9c 02303c 007250 00 
  A  0   0  4
   [ 5] .reloc            PROGBITS        fffea200 02a2a0 001204 00 
WA  0   0  1
...
Program Headers:
   Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg 
Align
   LOAD           0x0000a0 0xfffc0000 0xfffc0000 0x2d16c 0x35cd0 RWE 0x10
   LOAD           0x02d20c 0xfffff000 0xfffff000 0x01000 0x01000 R E 0x1
   GNU_STACK      0x000000 0x00000000 0x00000000 0x00000 0x00000 RWE 0x4

  Section to Segment mapping:
   Segment Sections...
    00     .text .rodata .reloc .data .data.rel.local 
.data.rel.ro.local .data.rel data .u_boot_cmd
    01     .resetvec .bootpg
    02


You see, the warnings are caused by the fact that the segment 01 has
address/size values which wraps to 0 in the following 'if' condition
introduced by the $subj in elfread.c, elf_symfile_segments():
...
&& vma < segments[j]->p_vaddr + segments[j]->p_memsz)


The place above is trivial to fix, but I wonder will be any
other consequences to the remote debugging of such kind of
images? (I can't try this at the moment)

Regards,
Sergei