Re: [Perfctr-devel] Re: [perfmon] perfmon2 code review: 32-bit ABI on 64-bit OS

David Gibson wrote:
On Sat, Feb 11, 2006 at 02:33:54PM -0800, Stephane Eranian wrote:
[...]
The most challenging piece is the IP (program pointer) that is in every
sample. Today it is defined as unsigned long because this is fairly
natural for a code address. The 64bit OS captures addresses as 64-bit,
the 32-bit monitoring tool running on top has to consume them as 64-bit
addresses, so u64 would be fine.

But not on a 32-bit kernel with a 32-bit tool, addresses exported as u64
would certainly work but consume double to buffer space, and that is a
more serious issue in my mind.

Hmm.. does the sampling buffer collect on userspace PC values, or
kernel ones as well?

Either, or both, depending on the measurement settings.

I live in a 64-bit world, so my take on this issue would be to expose
the PC as a uint64_t, always. There is already so much overhead in the
default per-sample header that I wouldn't worry about it.

Now 64 bit might not always be enough. E.g., on PA-RISC. But _I_ do
not care much about Linux on PA.

Eric

--
Eric Gouriou eric.gouriou@xxxxxx
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