Modify opcontrol to use a more inclusive kernel range

[Brian T. <tb...@us...>]

Hi,

When opcontrol invokes oprofiled, it specifies a range of valid
kernel addresses.  By default, the range is bounded by the start
and end of vmlinux's ".text" section.  The problem with this is
that some kernels (e.g. RHEL 5 x86_64) have multiple sections
containing text; for those kernels, samples are dropped for all
routines except those in the .text section, resulting in a misleading
profile.  The magnitude of this problem is significant; the RHEL 5
x86_64 kernel has over 10,000 sections containing text.  The implication
of this is that oprofile will drop samples for over 10,000 routines in
those kernels.

The attached patch modifies opcontrol, to make the end of the kernel
range the address of "_etext".  With a few exceptions (e.g. kernel
initialization code), this results in all kernel code being included in
the kernel range.

Before this patch, 30% of the kernel samples are thrown away for my
I/O benchmark.  After this patch, no kernel samples are thrown away.

Brian Twichell