* David Miller (davem@xxxxxxxxxxxxx) wrote: > From: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> > Date: Wed, 19 Jan 2011 00:08:45 -0500 > > > The following works fine for me now. Comments are welcome. > > Thanks for doing this work Mathieu. > > > - No aligned() type attribute nor variable attribute. I get a crash on x86_64 > > (NULL pointer exception when executing __trace_add_event_call, the 5th call). > > __alignof__(struct ftrace_event_call) is worth 8. > > This is really bizarre. Does it only happen on x86_64? Sadly, my ppc32 test machine is currently broken, so I could not check on other than x86 archs. > I'm wondering if GCC does something bizarre like work with different > default alignments based upon the section or something like that. > > If so, maybe adding the section attribute to the array definition will > "fix" things? Well, I thought about it in my sleep, and it looks like gcc is within its rights to align these statically declared structures on a larger alignment: gcc has no clue that we're going to do tricks with the linker to access the structures as an array, so aligning on a larger alignment *should* be fine for the compiler, but we suffer because we're doing something non-standard. > > > On 32-bit architectures, we really want a aligned(4), and on 64-bit > > architectures, aligned(8). Represent this by creating: > > > > #define __long_aligned __attribute__((__aligned__(__alignof__(long)))) > > Do any of these datastructures have, or will have, "u64" or "long > long" types in them? If so, then we will need to use "8" > unconditionally or "__alignof__(long long)". If my memory serves me correctly, I think "long long" is aligned on 4 bytes on ppc32, but on 8 bytes on x86_32 (yeah, that's weird). How about we create a #define __long_long_aligned __attribute__((__aligned__(__alignof__(long long)))) ? Thanks, Mathieu > > I'll see if I can work out why using no align directive explodes > on x86-64. -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
