Hi Philippe,
Back at work. See inline replies below.
> > > > > - powerpc32 updates for 2.6.30. Mainly to merge the once experimental
> > > > > bits that prevent most alignment faults from triggering a secondary
> > > > > mode
> > > > > switch. Andreas told me this works like a charm on 83xx, and I did not
> > > > > see any issue on 52xx, 85xx or 86xx either.
> > > > >
> > > >
> > > > Can I get a version of that patch for testing? Is it in your git
> > > > repository?
> > >
> > > I just pushed this commit to my remote tree (ipipe-2.6.30-powerpc
> > > branch); it should appear in a few hours once mirrored (cron job).
> > >
> >
> > I finally had a chance to test the ipipe-2.6.30-powerpc version
> > from the git repository. Unfortunately, I noticed that our application
> > dies after some time and that this behaviour is related to that
> > alignment patch (if I take it out everything runs fine for > 2 days).
> >
> > Currently I'm investigating the reasons for that crash. It has
> > something to do with floating point registers not being restored
> > properly. Our alignment exceptions are mainly triggered by accesses
> > to unaligned floating point data.
>
> Does it work any better with this patch in?
I applied that patch but unfortunately our application still dies. I included
an application with with you (hopefully) can reproduce the problem
which we are seeing. Our system is a MPC8360 with 2.6.30, ipipe 2.7,
xenomai 2.4.9.1.
Here are the steps:
1) apply ipipe with alignment patch, recompile kernel
2) comile test1.c (attached) with:
gcc -Wall -O2 `xeno-config --xeno-cflags` \
`xeno-config --xeno-ldflags` \
-l native -l rtdk -o test1 test1.c
3) Start test1 in one shell
4) Open a second shell and start 'switchbench'
Just when 'switchbench' is running, I get the following
output from my test application:
...
Missmatch: 0xfff8000082064000
Missmatch: 0xfff8000082064000
Missmatch: 0xfff8000082064000
Missmatch: 0xfff8000082064000
...
It seems that test1 is interrupted right between
the lfd and stfd and the floating point regs aren't
restored properly.
Just a side note: I had to add assembly code to my
C program to force an alignment exception. gcc seems
to be smart enough to avoid unaligned access. g++
on the other hand (especially g++ 3.3.6 which we are
using) seems to generate assembly code which causes
alignment exceptions. So it seems that it's really g++'s
fault. We also discovered that our g++ generates buggy
floating point assembly code when compiling with the
-O2 or -Os option. Currently, we compile our application
with -msoft-float to avoid those issues which has the
nice side effect that we also don't get alignment exceptions
anymore.
Many thanks,
Andreas
> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index 32cc3df..a04a5e3 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -80,7 +80,9 @@ void flush_fp_to_thread(struct task_struct *tsk)
> * FPU, and then when we get scheduled again we would store
> * bogus values for the remaining FP registers.
> */
> - ipipe_preempt_disable(flags);
> + if (ipipe_root_domain_p)
> + preempt_disable();
> + local_irq_save_hw_cond(flags);
> if (tsk->thread.regs->msr & MSR_FP) {
> #ifdef CONFIG_SMP
> /*
> @@ -94,7 +96,9 @@ void flush_fp_to_thread(struct task_struct *tsk)
> #endif
> giveup_fpu(tsk);
> }
> - ipipe_preempt_enable(flags);
> + local_irq_restore_hw_cond(flags);
> + if (ipipe_root_domain_p)
> + preempt_enable();
> }
> }
/* vim: set ts = 4: */
#include <sys/mman.h>
#include <unistd.h>
#include <signal.h>
#include <string.h>
#include <stdarg.h>
#include <rtdk.h>
#include <native/task.h>
typedef struct msg {
unsigned char id;
union {
unsigned long long raw;
struct {
unsigned short val1;
unsigned long val2;
unsigned short val3;
} __attribute__((packed));
};
} __attribute__((packed)) msg_t;
static RT_TASK task;
static msg_t msg;
int main(void)
{
int err;
mlockall(MCL_CURRENT|MCL_FUTURE);
rt_print_auto_init(1);
err = rt_task_shadow(&task, "main", 3, 0);
if(!err) {
/* Fill the message */
msg.id = 0xFF;
msg.val1 = 0x1234;
msg.val2 = 0x56789ABC;
msg.val3 = 0xDEF0;
while(1) {
double save;
unsigned long long out = 0;
/* Force an alignment exception
by accessing unaligned floating
point data (lfd 0,1(%2)). */
__asm__ __volatile__(
"stfd 0,%0 # save contents of f0 \n\t"
"lfd 0,1(%2) # unaligned access \n\t"
"stfd 0,%1 # store data in 'out' \n\t"
"lfd 0,%0 # restore contents of f0 \n\t"
: "=m"(save), "=m"(out)
: "r"(&msg)
);
if( out != msg.raw )
rt_printf("Missmatch: 0x%llx\n", out);
rt_task_sleep(100000ULL);
}
}
return err;
}
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