[Valgrind-developers] location of /lib/tls/libc.so

[Nicholas N. <nj...@ca...>]

Hi,

On my machine, it seems that /lib/tls/libc.so is always put at address 
0x42000000.  All other .so files seem to move around and get put near the 
base of the mmap-segment.  Here's an example -- with Memcheck, here the 
mmap-segment starts at 0x1b8e4000, and all the other .so files are put 
around there, but /lib/tlc/libc.so isn't:

08048000-08049000 r-xp 00000000 00:0e 4309378    /auto/homes/njn25/grind/head6/mmap
08049000-0804a000 rw-p 00000000 00:0e 4309378    /auto/homes/njn25/grind/head6/mmap
1b8e4000-1b8f9000 r-xp 00000000 09:03 74918      /lib/ld-2.3.2.so
1b8f9000-1b8fa000 rw-p 00015000 09:03 74918      /lib/ld-2.3.2.so
1b8fb000-1b8fc000 rw-p 00000000 00:00 0
1b8fd000-1b8fe000 r-xp 00000000 00:0e 12496364   /auto/homes/njn25/grind/head6/coregrind/vg_inject.so
1b8fe000-1b8ff000 rw-p 00000000 00:0e 12496364   /auto/homes/njn25/grind/head6/coregrind/vg_inject.so
1b900000-1b905000 r-xp 00000000 00:0e 7789291    /auto/homes/njn25/grind/head6/memcheck/vgpreload_memcheck.so
1b905000-1b906000 rw-p 00004000 00:0e 7789291    /auto/homes/njn25/grind/head6/memcheck/vgpreload_memcheck.so
1b907000-1b908000 rw-p 00000000 00:00 0
1b913000-1b914000 rw-p 00000000 00:00 0
42000000-42130000 r-xp 00000000 09:03 75056      /lib/tls/libc-2.3.2.so
42130000-42133000 rw-p 00130000 09:03 75056      /lib/tls/libc-2.3.2.so
42133000-42136000 rw-p 00000000 00:00 0

This is a bit frustrating because it often cuts the mmap-segment into two 
pieces unnecessarily, which reduces the size of the biggest mmap that can 
be made.

Any ideas why this might be so?  I guess this could be mapped in with with 
MAP_FIXED... I tried tweaking things so that 0x42000000 isn't available to 
the client (by artificially inflating Memcheck's shadow memory needs) and 
I got this:

   date: error while loading shared libraries: libc.so.6: failed to map
   segment from shared object: Cannot allocate memory

It's probably out of our control, which I can live with, ok, but I am 
curious as to why this is happening.

N