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

Phil,

On Tue, Feb 14, 2006 at 12:57:55AM +0600, Philip Mucci wrote:
Stefane,

I know this is ugly, but what about in the user code checking the arch?
Is it not true that if a kernel is running 64 bit, it has the 64 tagged
on the the end of the arch? i.e. mips64, ppc64, x86_64?

The other solution would be to add am information call to the API, like
perfctr has. This would export the processor type along with other
feature bits, including the number of bits of the IP.


The problem is at compile time and not so much at runtime.
Take a kernel struct that is shared with user (i.e., passed through syscall)
that has the following layout:

struct foo {
unsigned long bar;
int dummy;
};

For a 64-bit app on a 64-bit OS OR a 32-bit app on a 32-bit OS, this works
perfectly.

For a 32-bit on a 64-bit OS, there is a problem, the 32-bit app must be compiled
with the following definition instead:
struct foo {
unsigned long long bar;
int dummy;
};

to share the struct with the 64-bit OS. An application compile with the above
struct, would not work when run on a 32-bit OS.

So I think that we need to replace all unsigned long, size_t, void * by uint64_t
to make sure this works either way. It is overkill on pure 32-bit but ensures
that the application can be migrated over to a 64-bit OS without the need for
special recompilation.

--
-Stephane
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