[Linux-ia64] fpswa logging redux

[Linux-ia64] fpswa logging redux

[Jesse Barnes]

I've recently had some requests from people running apps on our ia64
boxes for more detailed fpswa fault information.  Currently, the ia64
kernel will print up to a certain number of fpswa fault messages per
tick, with ip information about where the fault came from.  The user can
also choose to be notified of faults via a SIGFPE signal, but the
si_info field of the siginfo structure doesn't contain enough
information about the fault to be useful.

I'd like to fully decode the information in the isr about what type of
fault occured (whether it be a software assist fault, some sort of IEEE
filter fault, etc.) and print it along with the ip when faults occur.
While I'm at it, I may as well the proper SIGFPE subcode into si_info in
case of signal delivery is selected.

Comments?  David & Bjorn, do you think this would be useful enough to
get into the tree?

Thanks,
Jesse

Re: [Linux-ia64] fpswa logging redux

[Keith Owens]

On Wed, 11 Dec 2002 14:25:14 -0800, 
Jesse Barnes <jbarnes@sgi.com> wrote:
>I've recently had some requests from people running apps on our ia64
>boxes for more detailed fpswa fault information.  Currently, the ia64
>kernel will print up to a certain number of fpswa fault messages per
>tick, with ip information about where the fault came from.  The user can
>also choose to be notified of faults via a SIGFPE signal, but the
>si_info field of the siginfo structure doesn't contain enough
>information about the fault to be useful.
>
>I'd like to fully decode the information in the isr about what type of
>fault occured (whether it be a software assist fault, some sort of IEEE
>filter fault, etc.) and print it along with the ip when faults occur.
>While I'm at it, I may as well the proper SIGFPE subcode into si_info in
>case of signal delivery is selected.

I have a couple of Perl scripts for decoding isr and psr.  They read
hex values (with or without the leading 0x) from stdin and pretty print
the result.

--- ia64_isr ---

#!/usr/bin/perl -w
use strict;
use integer;

my @fields = (
	[ 0, 16, "Code" ],
	[ 16, 8, "Vector" ],
	[ 24, 8, "rv" ],
	[ 32, 1, "x" ],
	[ 33, 1, "w" ],
	[ 34, 1, "r" ],
	[ 35, 1, "na" ],
	[ 36, 1, "sp" ],
	[ 37, 1, "rs" ],
	[ 39, 1, "ni" ],
	[ 40, 1, "so" ],
	[ 41, 2, "ei" ],
	[ 43, 1, "ed" ],
	[ 44, 20, "rv" ],
	);

while (defined($_ = <STDIN>)) {
	chomp();
	s/^0[xX]//;
	my $w0 = hex(substr($_, 0, -8));
	my $w1 = hex(substr($_, -8));
	printf("isr %s\n", $_);
	&ia64_isr($w1, 0, 32);
	&ia64_isr($w0, 32, 64);
}

sub ia64_isr()
{
	my ($w, $s, $e) = @_;
	my $v;
	foreach (@fields) {
		next if ($_->[0] >= $e || $_->[0] < $s);
		# use integer implies signed shift, I want unsigned
		no integer;
		$v = ($w >> ($_->[0] - $s)) & (~0 >> (32 - $_->[1]));
		printf("%2d %2d %12s %x\n", $_->[0], $_->[1], $_->[2], $v);
	}
}

--- ia64_psr ---

#!/usr/bin/perl -w
use strict;
use integer;

my @fields = (
	[ 0, 6, "User mask" ],
	[ 0, 1, "rv" ],
	[ 1, 1, "be" ],
	[ 2, 1, "up" ],
	[ 3, 1, "ac" ],
	[ 4, 1, "mfl" ],
	[ 5, 1, "mfh" ],
	[ 0, 24, "System mask" ],
	[ 6, 6, "rv" ],
	[ 13, 1, "ic" ],
	[ 14, 1, "i" ],
	[ 15, 1, "pk" ],
	[ 16, 1, "rv" ],
	[ 17, 1, "dt" ],
	[ 18, 1, "dfl" ],
	[ 19, 1, "dfh" ],
	[ 20, 1, "sp" ],
	[ 21, 1, "pp" ],
	[ 22, 1, "di" ],
	[ 23, 1, "si" ],
	[ 24, 1, "db" ],
	[ 25, 1, "lp" ],
	[ 26, 1, "tb" ],
	[ 27, 1, "rt" ],
	[ 28, 4, "rv" ],
	[ 32, 2, "cpl" ],
	[ 34, 1, "is" ],
	[ 35, 1, "mc" ],
	[ 36, 1, "it" ],
	[ 37, 1, "id" ],
	[ 38, 1, "da" ],
	[ 39, 1, "dd" ],
	[ 40, 1, "ss" ],
	[ 41, 2, "ri" ],
	[ 43, 1, "ed" ],
	[ 44, 1, "bn" ],
	[ 45, 1, "ia" ],
	[ 46, 18, "rv" ]
	);

while (defined($_ = <STDIN>)) {
	chomp();
	s/^0[xX]//;
	my $w0 = hex(substr($_, 0, -8));
	my $w1 = hex(substr($_, -8));
	printf("psr %s\n", $_);
	&ia64_psr($w1, 0, 32);
	&ia64_psr($w0, 32, 64);
}

sub ia64_psr()
{
	my ($w, $s, $e) = @_;
	my $v;
	foreach (@fields) {
		next if ($_->[0] >= $e || $_->[0] < $s);
		# use integer implies signed shift, I want unsigned
		no integer;
		$v = ($w >> ($_->[0] - $s)) & (~0 >> (32 - $_->[1]));
		printf("%2d %2d %12s %x\n", $_->[0], $_->[1], $_->[2], $v);
	}
}

Re: [Linux-ia64] fpswa logging redux

[Jesse Barnes]

On Thu, Dec 12, 2002 at 10:07:57AM +1100, Keith Owens wrote:
> I have a couple of Perl scripts for decoding isr and psr.  They read
> hex values (with or without the leading 0x) from stdin and pretty print
> the result.

It's the isr code field I'm particularly interested in.  For fp faults
and traps, I'd like to decode what type of fault/trap occured and add it
to the printk, e.g.
Dec 11 17:11:05 morale kernel: a.out(1901): floating-point assist trap : ip@00000000000752
Dec 11 17:11:05 morale kernel: a.out(1901): floating-point assist fault : software assist ip@00000000000c01

Jesse

Re: [Linux-ia64] fpswa logging redux

[Keith Owens]

On Wed, 11 Dec 2002 15:12:18 -0800, 
Jesse Barnes <jbarnes@sgi.com> wrote:
>On Thu, Dec 12, 2002 at 10:07:57AM +1100, Keith Owens wrote:
>> I have a couple of Perl scripts for decoding isr and psr.  They read
>> hex values (with or without the leading 0x) from stdin and pretty print
>> the result.
>
>It's the isr code field I'm particularly interested in.  For fp faults
>and traps, I'd like to decode what type of fault/trap occured and add it
>to the printk, e.g.
>Dec 11 17:11:05 morale kernel: a.out(1901): floating-point assist trap : ip@00000000000752
>Dec 11 17:11:05 morale kernel: a.out(1901): floating-point assist fault : software assist ip@00000000000c01

The general approach is that the kernel prints raw values and user
space decodes them, unless there is some overriding reason to do it in
kernel.  IOW, print the isr in the kernel but decode it using the
scripts or equivalent.

Re: [Linux-ia64] fpswa logging redux

[Jesse Barnes]

On Thu, Dec 12, 2002 at 10:17:20AM +1100, Keith Owens wrote:
> On Wed, 11 Dec 2002 15:12:18 -0800, 
> Jesse Barnes <jbarnes@sgi.com> wrote:
> >On Thu, Dec 12, 2002 at 10:07:57AM +1100, Keith Owens wrote:
> >> I have a couple of Perl scripts for decoding isr and psr.  They read
> >> hex values (with or without the leading 0x) from stdin and pretty print
> >> the result.
> >
> >It's the isr code field I'm particularly interested in.  For fp faults
> >and traps, I'd like to decode what type of fault/trap occured and add it
> >to the printk, e.g.
> >Dec 11 17:11:05 morale kernel: a.out(1901): floating-point assist trap : ip@00000000000752
> >Dec 11 17:11:05 morale kernel: a.out(1901): floating-point assist fault : software assist ip@00000000000c01
> 
> The general approach is that the kernel prints raw values and user
> space decodes them, unless there is some overriding reason to do it in
> kernel.  IOW, print the isr in the kernel but decode it using the
> scripts or equivalent.

But if we do that the si_code field of siginfo won't have useful
information.  My thought was that if we decode isr in enough detail to
fill in si_code correctly, we may as well make the printks more useful
as well.  I think all this stuff would be in arch/ia64/kernel/traps.c,
with the possible exception of another SIGFPE code for software assist
faults (and maybe denormal/unnormal).

Thanks,
Jesse

Re: [Linux-ia64] fpswa logging redux

[David Mosberger]

>>>>> On Wed, 11 Dec 2002 14:25:14 -0800, Jesse Barnes <jbarnes@sgi.com> said:

  Jesse> I'd like to fully decode the information in the isr about
  Jesse> what type of fault occured (whether it be a software assist
  Jesse> fault, some sort of IEEE filter fault, etc.) and print it
  Jesse> along with the ip when faults occur.  While I'm at it, I may
  Jesse> as well the proper SIGFPE subcode into si_info in case of
  Jesse> signal delivery is selected.

Like Keith, I'd like to keep the amount of decoding in the kernel as
minimal as possible.  We already have si_isr in the siginfo structure,
so apps/libraries can decode things themselves.  Having said that, we
ought to decode things sufficiently so that si_code can be set to the
correct value (where this makes sense).  Hopefully, that won't add
tons of code and it would help application portability.

	--david

Re: [Linux-ia64] fpswa logging redux

[Jesse Barnes]

[-- Attachment #1: Type: text/plain, Size: 1183 bytes --]

On Wed, Dec 11, 2002 at 03:42:52PM -0800, David Mosberger wrote:
> >>>>> On Wed, 11 Dec 2002 14:25:14 -0800, Jesse Barnes <jbarnes@sgi.com> said:
> 
>   Jesse> I'd like to fully decode the information in the isr about
>   Jesse> what type of fault occured (whether it be a software assist
>   Jesse> fault, some sort of IEEE filter fault, etc.) and print it
>   Jesse> along with the ip when faults occur.  While I'm at it, I may
>   Jesse> as well the proper SIGFPE subcode into si_info in case of
>   Jesse> signal delivery is selected.
> 
> Like Keith, I'd like to keep the amount of decoding in the kernel as
> minimal as possible.  We already have si_isr in the siginfo structure,
> so apps/libraries can decode things themselves.  Having said that, we
> ought to decode things sufficiently so that si_code can be set to the
> correct value (where this makes sense).  Hopefully, that won't add
> tons of code and it would help application portability.

How about something like this then?  It just prints out the isr in
addition to the ip for the case of printk, and decodes the right si_code
for signals.  If this approach looks ok, I can add trap decoding too.

Thanks,
Jesse

[-- Attachment #2: fpswa-si_code-decode-2.4.19-ia64.patch --]
[-- Type: text/plain, Size: 3059 bytes --]

diff -Naur -X /home/jbarnes/dontdiff linux-2.4.19-ia64/arch/ia64/kernel/traps.c linux-2.4.19-ia64-fpswa/arch/ia64/kernel/traps.c
--- linux-2.4.19-ia64/arch/ia64/kernel/traps.c	Thu Dec 12 10:15:57 2002
+++ linux-2.4.19-ia64-fpswa/arch/ia64/kernel/traps.c	Thu Dec 12 10:23:25 2002
@@ -45,6 +45,34 @@
 
 static fpswa_interface_t *fpswa_interface;
 
+/*
+ * fp fault isr.code <-> siginfo.si_code mapping
+ */
+struct fp_fault_info fp_fault_info[] = {
+	{ 1<<0, FPE_FLTINV },
+	{ 1<<1, FPE_DENORM },
+	{ 1<<2, FPE_FLTDIV },
+	{ 1<<3, FPE_SWASST },
+	{ 1<<4, FPE_FLTINV },
+	{ 1<<5, FPE_DENORM },
+	{ 1<<6, FPE_FLTDIV },
+	{ 1<<7, FPE_SWASST },
+};
+
+static inline int
+fp_fault_si_code(__u64 isr)
+{
+	int i, ret = 0;
+	int nr_entries;
+	nr_entries = sizeof(fp_fault_info)/sizeof(struct fp_fault_info);
+	
+	for (i = 0; i < nr_entries; i++) {
+		if (isr & fp_fault_info[i].isr_code_bit)
+			ret |= fp_fault_info[i].si_code;
+	}
+	return ret;
+}
+
 void __init
 trap_init (void)
 {
@@ -336,8 +364,9 @@
 		fpu_swa_count = 0;
 	if ((++fpu_swa_count < 5) && !(current->thread.flags & IA64_THREAD_FPEMU_NOPRINT)) {
 		last_time = jiffies;
-		printk(KERN_WARNING "%s(%d): floating-point assist fault at ip %016lx\n",
-		       current->comm, current->pid, regs->cr_iip + ia64_psr(regs)->ri);
+		printk(KERN_WARNING "%s(%d): floating-point assist %s ",
+		       current->comm, current->pid, fp_fault ? "fault:" : "trap");
+		printk("ip=%016lx, isr=%16lx\n", regs->cr_iip + ia64_psr(regs)->ri, isr);
 	}
 
 	exception = fp_emulate(fp_fault, bundle, &regs->cr_ipsr, &regs->ar_fpsr, &isr, &regs->pr,
@@ -556,6 +585,8 @@
 			siginfo.si_signo = SIGFPE;
 			siginfo.si_errno = 0;
 			siginfo.si_code = FPE_FLTINV;
+			if (vector == 32) /* decode fault into si_code */
+				siginfo.si_code = fp_fault_si_code(isr);
 			siginfo.si_addr = (void *) (regs->cr_iip + ia64_psr(regs)->ri);
 			siginfo.si_flags = __ISR_VALID;
 			siginfo.si_isr = isr;
diff -Naur -X /home/jbarnes/dontdiff linux-2.4.19-ia64/include/asm-ia64/fpu.h linux-2.4.19-ia64-fpswa/include/asm-ia64/fpu.h
--- linux-2.4.19-ia64/include/asm-ia64/fpu.h	Sun Feb  6 18:42:40 2000
+++ linux-2.4.19-ia64-fpswa/include/asm-ia64/fpu.h	Thu Dec 12 10:11:45 2002
@@ -54,6 +54,11 @@
 
 # ifndef __ASSEMBLY__
 
+struct fp_fault_info {
+	unsigned long isr_code_bit;
+	int si_code; /* SIGFPE si_code */
+};
+
 struct ia64_fpreg {
 	union {
 		unsigned long bits[2];
diff -Naur -X /home/jbarnes/dontdiff linux-2.4.19-ia64/include/asm-ia64/siginfo.h linux-2.4.19-ia64-fpswa/include/asm-ia64/siginfo.h
--- linux-2.4.19-ia64/include/asm-ia64/siginfo.h	Thu Dec 12 10:15:59 2002
+++ linux-2.4.19-ia64-fpswa/include/asm-ia64/siginfo.h	Thu Dec 12 10:19:47 2002
@@ -172,6 +172,8 @@
 #define __FPE_DECERR	(__SI_FAULT|11)	/* packed decimal error */
 #define __FPE_INVASC	(__SI_FAULT|12)	/* invalid ASCII digit */
 #define __FPE_INVDEC	(__SI_FAULT|13)	/* invalid decimal digit */
+#define FPE_SWASST	(__SI_FAULT|14) /* software assist fault */
+#define FPE_DENORM	(__SI_FAULT|15) /* denormal/unnormal operand */
 #define NSIGFPE		13
 
 /*

Re: [Linux-ia64] fpswa logging redux

[David Mosberger]

  Jesse> How about something like this then?  It just prints out the
  Jesse> isr in addition to the ip for the case of printk, and decodes
  Jesse> the right si_code for signals.  If this approach looks ok, I
  Jesse> can add trap decoding too.

Basically OK with me, however:

 o What's the point of declaring fp_fault_info in a header file?  It's
   used only in one place.

 o si_code is NOT a bitmask; it makes no sense at all for
   fp_fault_si_code() to OR multiple values together; this makes me
   highly suspicious that there is a misunderstanding somewhere...

 o Who defined FP_SWASST and FPE_DENORM?  I don't recall seeing them
   in the ia64 psABI and they definitely look ia64-specific, so their
   names should at least be prefixed by a double-underscore
   (siginfo.h).

 o If you add stuff to asm/siginfo.h, don't forget to update glibc (in
   sysdeps/unix/sysv/linux/ia64/bits/siginfo.h).

	--david