text/data segments in cygnus executables

Fergus Henderson fjh@cs.mu.OZ.AU
Tue Aug 31 23:49:00 GMT 1999

On 05-Aug-1999, Read, Gordon <GRead@Broner.co.uk> wrote:
> I need to find out the addresses of the the various segments in the
> currently running process (i.e. the start address of the text segment, data
> segment and so on), these are the values reported by "size -A program.exe".
> How do I do this from within a C program compiled using gcc under cygnus?

The start and end of the data and bss segments are contained in the
symbols __data_start__, __data_end__, __bss_start__, and __bss_end__.
I think there are other symbols like these; check the linker script for
details.  (I think there's an option to `ld' to get it to dump the linker
script, but if not, you could try using strace to see what files `ld' reads,
or looking at the `ld' source code.)

You can access these symbols from C program using declarations
like the following:

	extern char _data_start__[];
	extern char _data_end__[];
	extern char _bss_start__[];
	extern char _bss_end__[];

	int main() {
		printf("data start = %p\n", (void *) _data_start__);

For an example of their use, check the definitions of DATASTART and DATAEND
for CYGWIN in the file config.h from gc.tar.gz available at
http://reality.sgi.com/boehm/gc.html .

Fergus Henderson <fjh@cs.mu.oz.au>  |  "I have always known that the pursuit
WWW: < http://www.cs.mu.oz.au/~fjh >  |  of excellence is a lethal habit"
PGP: finger fjh@        |     -- the last words of T. S. Garp.

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