Re: [User-mode-linux-devel] UML/PPC status

[Chris E. <cem...@ch...>]

On Mon, 1 May 2000, Jeff Dike wrote:

> What's going on here is that the kernel is copying its data and bss into two 
> files, unmapping them, and then mapping those files shared in their places.  
> This is to make the kernel data shared across forks.  Otherwise, they would 
> end up copy-on-write.

Ok, that makes sense.

> remap_data recognizes the appropriate maps by their permissions.  It
> looks like another method is needed for ppc.
> 
> It looks like there is no separate text and data in the maps.  Just
> text, bss, and stack.  Is that right?

It may be something odd about the linux binary.  The maps from /bin/ls
look a bit more interesting.  One difference is the dynamic linking -
linux seems to be static.

0fee8000-0ffc9000 r-xp 00000000 03:09 120950     /lib/libc-2.1.3.so
0ffc9000-0ffd8000 ---p 000e1000 03:09 120950     /lib/libc-2.1.3.so
0ffd8000-0ffeb000 rwxp 000e0000 03:09 120950     /lib/libc-2.1.3.so
0ffeb000-0fff0000 rwxp 00000000 00:00 0
10000000-1000c000 r-xp 00000000 03:09 30304      /bin/ls
1001b000-1001d000 rwxp 0000b000 03:09 30304      /bin/ls
30000000-30014000 r-xp 00000000 03:09 120833     /lib/ld-2.1.3.so
30014000-30015000 rw-p 00000000 00:00 0
30023000-30027000 rwxp 00013000 03:09 120833     /lib/ld-2.1.3.so
7fffe000-80000000 rwxp fffff000 00:00 0

> Why don't we just ditch the permissions comparisons and use _etext
> and _end.  The region between _etext and _end is the data, so just
> fiddle remap_data to remap that.

Do you want to do that?  :-)

> > Is something actually wrong here, or should it only exit if both
> > remap_data("rwx") and remap_data("rw-") fail? 
> They both have to succeed.

Ok.

Chris
-- 
Chris Emerson, obsessed Cambridge juggler
E-mail: cem...@ch...
Web page: http://www.chiark.greenend.org.uk/~cemerson/