Re: print_ubacktrace() and ppc 32

[Lukas Berk <lberk@redhat.com>]

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Hey,

> On Mon, 2013-06-17 at 16:24 +0200, Holger Brunck wrote:
> > I am using systemtap userspace probes on a 32-Bit powerpc architecture. I do
> > crosscompile the probes on a 64-Bit x86 host.
> > 
> > The version I use is:
> > Systemtap translator/driver (version 2.3/0.152, non-git sources)
> > 
> > If I use print_ubacktrace() in my stap script it won't compile. I am getting two
> > main error messages and I ask myself which one tells me the real reason for the
> > error:
> > 
> > backtraces for 32bit programs on 64bit kernels don't work.
> 
> Yes, if your powerpc kernel is 64bit, but the user program is 32bit
> (same for 32bit user space on x86_64) then you will get that warning
> during stap translation time (the stap script should still run, but
> won't produce a user backtrace for the 32bit module/library/process).
> This is bug: http://sourceware.org/bugzilla/show_bug.cgi?id=10272
> "backtraces fail with 32-on-64 executables"
> 
> > systemtap-2.3-32645/share/systemtap/runtime/stack.c:85:2: error: #error
> > "Unsupported architecture"
> 
> This might be caused by the cross compiling, maybe something got
> confused about the architecture. You get that when:
> #ifndef STP_USE_DWARF_UNWINDER
> powerpc (and x86_64) both should use the DWARF_UNWINDER. So you might
> want to look at why that doesn't get defined in your case.

Unfortunately I believe this is because we don't actually support
powerpc32 (only ppc64.h is defined in unwind.h).  So while the first
error you're getting is being worked on (I'm currently working on
PR10272[1] so hopefully it'll be resloved soon), the second error will
be the show stopper here.  

Thanks,

Lukas

[1] - http://sourceware.org/bugzilla/show_bug.cgi?id=10272

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