Thanks for your response.
This is the output from readelf
mipsel-linux-readelf -S helloworldmips
There are 29 section headers, starting at offset 0x1290:
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 004000f4 0000f4 000014 00 A 0 0 1
[ 2] .reginfo MIPS_REGINFO 00400108 000108 000018 18 A 0 0 4
[ 3] .dynamic DYNAMIC 00400120 000120 0000f8 08 A 6 0 4
[ 4] .hash HASH 00400218 000218 0000b4 04 A 5 0 4
[ 5] .dynsym DYNSYM 004002cc 0002cc 0001a0 10 A 6 1 4
[ 6] .dynstr STRTAB 0040046c 00046c 00011b 00 A 0 0 1
[ 7] .gnu.version VERSYM 00400588 000588 000034 02 A 5 0 2
[ 8] .gnu.version_r VERNEED 004005bc 0005bc 000020 00 A 6 1 4
[ 9] .init PROGBITS 004005dc 0005dc 000088 00 AX 0 0 4
[10] .text PROGBITS 00400670 000670 0004c0 00 AX 0 0 16
[11] .MIPS.stubs PROGBITS 00400b30 000b30 000070 00 AX 0 0 4
[12] .fini PROGBITS 00400ba0 000ba0 000058 00 AX 0 0 4
[13] .rodata PROGBITS 00400c00 000c00 0000f0 00 A 0 0 16
[14] .eh_frame PROGBITS 00400cf0 000cf0 000004 00 A 0 0 4
[15] .ctors PROGBITS 10000000 001000 000008 00 WA 0 0 4
[16] .dtors PROGBITS 10000008 001008 000008 00 WA 0 0 4
[17] .jcr PROGBITS 10000010 001010 000004 00 WA 0 0 4
[18] .data PROGBITS 10000020 001020 000030 00 WA 0 0 16
[19] .rld_map PROGBITS 10000050 001050 000004 00 WA 0 0 4
[20] .got PROGBITS 10000060 001060 00004c 04 WAp 0 0 16
[21] .sbss NOBITS 100000ac 0010ac 000000 00 WAp 0 0 1
[22] .bss NOBITS 100000b0 0010ac 000020 00 WA 0 0 16
[23] .comment PROGBITS 00000000 0010ac 00005a 00 0 0 1
[24] .pdr PROGBITS 00000000 001108 0000a0 00 0 0 4
[25] .mdebug.abi32 PROGBITS 00000000 0011a8 000000 00 0 0 1
[26] .shstrtab STRTAB 00000000 0011a8 0000e5 00 0 0 1
[27] .symtab SYMTAB 00000000 001718 000500 10 28 51 4
[28] .strtab STRTAB 00000000 001c18 00023f 00 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings)
I (info), L (link order), G (group), x (unknown)
O (extra OS processing required) o (OS specific), p (processor specific)
This one tells me that the bss is writable?? Can you giev me a direction where the problem is??
Cheers,
On 9/7/06, Ralf Baechle <ralf@xxxxxxxxxxxxxx> wrote:
On Tue, Sep 05, 2006 at 08:55:18AM +0200, Erik Niessen wrote:
> /helloworldmips(86)
> 00400000 (4 KB) r-xp (00:0a 33243002) linux/test/helloworldmips
> 10000000 (4 KB) rw-p (00:0a 33243002) linux/test/helloworldmips
> 10001000 (4 KB) rwxp (00:00 0) [heap]
> 2aaa8000 (20 KB) r-xp (00:07 1795853)
> /lib/ld-uClibc-0.9.27.so< http://uclibc-0.9.27.so/>
> 2aaad000 (4 KB) rw-p (00:00 0)
> 2aaed000 (4 KB) rw-p (00:07 1795853) /lib/ld-
> uClibc-0.9.27.so< http://uclibc-0.9.27.so/>
> 2aaee000 (48 KB) r-xp (00:07 1795861) /lib/libgcc_s.so.1
> 2aafa000 (252 KB) ---p (00:00 0)
> 2ab39000 (4 KB) rw-p (00:07 1795861) /lib/libgcc_s.so.1
> 2ab3a000 (368 KB) r-xp (00:07 1795855) /lib/libuClibc-0.9.27.so
> 2ab96000 (256 KB) ---p (00:00 0)
> 2abd6000 (8 KB) rw-p (00:07 1795855) /lib/libuClibc- 0.9.27.so
> 2abd8000 (16 KB) rw-p (00:00 0)
> 7fd49000 (84 KB) rwxp (00:00 0) [stack]
> mapped: 1076 KB writable/private: 128 KB shared: 0 KB
>
> It seems that the bss segments of the shared libs are protected and mapped
> to the zero page. I don't see this
> when I run this on a linux pc. I have the following questions:
> - Why is this segment protected? Accessing results in a seg fault.
Protecting a bss segment doesn't make sense.
The address and the "---p" flags make me suspect your executable might
actually be wrong, so I suggest you check the binary with something like
readelf -S.
> - Why is it so big (252k/256K)?
> - How much memory is physically allocated for this segment?
None at this stage - the actuall allocation would happen lazily when
a page is touched first which of course doesn't ever happen in your
case.
Ralf
