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Subjectalpha/2.4.x: CPU misdetection, possible miscompilation
Hi,

trying to boot any 2.4.x kernel on a Tsunami DP264 alpha with dual EV67,
we found the following problems:

CPU misdetection:

On our machine the cpu->type field contains 0x80000000B
(= 2^35 + 11) instead of 0xB (= hwrpb.h: #define EV67_CPU 11).

The spurious high bit leads to false/default values for
on_chip_cache in smp.c:smp_tune_scheduling.

possible miscompilation of smp_tune_scheduling:

These versions of gcc

gcc version 2.95.3 20010111
gcc version 2.95.4 20010506

miscompile the 'switch (cpu->type)' in smp_tune_scheduling, which
leads to a reproducible oops on 2.4.4, 2.4.5pre2 and 2.4.5pre2aa1.

Please find a goofy gcc workaround and an attempted cpu->type fix below.

As a side note, the value of smp.c:smp_tune_scheduling:on_chip_cache is
not used in 2.4.5pre2 and 2.4.5pre2aa1.

Greetings, Mike


=== gcc workaround / goofy ===

Inserting an debug statement leads to correct compilation of
smp_tune_scheduling:


--- tmp/linux/arch/alpha/kernel/smp.c Wed May 16 17:24:28 2001
+++ linux-2.4.5pre2aa1/arch/alpha/kernel/smp.c Wed May 16 18:06:59 2001
@@ -36,7 +36,7 @@
#include "irq_impl.h"


-#define DEBUG_SMP 0
+#define DEBUG_SMP 1
#if DEBUG_SMP
#define DBGS(args) printk args
#else
@@ -239,6 +239,7 @@
break;

default:
+ DBGS(("cpu->type = %lx\n", cpu->type));
on_chip_cache = 8 + 8;
break;
}


=== Fix for cpu->type ===

Masking cpu->type seems to work for this machine, but limiting the
cpu->type seems rather arbitrary.


--- tmp/linux/arch/alpha/kernel/smp.c Wed May 16 17:24:28 2001
+++ linux-2.4.5pre2aa1/arch/alpha/kernel/smp.c Wed May 16 18:24:49 2001
@@ -35,6 +35,8 @@
#include "proto.h"
#include "irq_impl.h"

+/* mask for cpu->type (arbitrary assumption based on #define's in hwrpb.h) */
+#define CPU_TYPE_MASK 0xFFFFFF

#define DEBUG_SMP 0
#if DEBUG_SMP
@@ -218,7 +220,7 @@
unsigned long freq;

cpu = (struct percpu_struct*)((char*)hwrpb + hwrpb->processor_offset);
- switch (cpu->type)
+ switch (cpu->type & CPU_TYPE_MASK)
{
case EV45_CPU:
on_chip_cache = 16 + 16;

==== dmesg output begin ====
aboot: loading uncompressed vmlinux7...
aboot: segment 0, 2907516 bytes at 0xfffffc0000310000
aboot: zero-filling 1212636 bytes at fffffc00005d5d7c
aboot: starting kernel vmlinuz7 with arguments ro root=/dev/sda3
console=ttyS0
Linux version 2.4.5-pre2aa1 (mike@haring) (gcc version 2.95.4 20010506
(Debian prerelease)) #1 SMP Wed May 16 13:37:27 CEST 2001
Booting GENERIC on Tsunami variation DP264 using machine vector DP264 from
SRM
Command line: ro root=/dev/sda3 console=ttyS0
memcluster 0, usage 1, start 0, end 256
memcluster 1, usage 0, start 256, end 130979
memcluster 2, usage 1, start 130979, end 131072
memcluster 3, usage 0, start 131072, end 393212
memcluster 4, usage 1, start 393212, end 393216
freeing pages 256:384
freeing pages 897:130979
freeing pages 131072:393212
reserving pages 897:903
SMP: 2 CPUs probed -- cpu_present_mask = 3
On node 0 totalpages: 393212
zone(0): 393212 pages.
zone(1): 0 pages.
zone(2): 0 pages.
Kernel command line: ro root=/dev/sda3 console=ttyS0
Using epoch = 1900
Console: colour VGA+ 80x25
Calibrating delay loop... 1326.92 BogoMIPS
Memory: 3086216k/3145696k available (1817k kernel code, 56688k reserved,
583k data, 384k init)
Dentry-cache hash table entries: 262144 (order: 9, 4194304 bytes)
Buffer-cache hash table entries: 262144 (order: 8, 2097152 bytes)
Page-cache hash table entries: 524288 (order: 9, 4194304 bytes)
Inode-cache hash table entries: 262144 (order: 9, 4194304 bytes)
POSIX conformance testing by UNIFIX
Unable to handle kernel paging request at virtual address 0000000000000000
CPU 0 swapper(0): Oops 0
pc = [<fffffc00004e44e8>] ra = [<fffffc00004e4c54>] ps = 0000
v0 = fffffc0000564000 t0 = 0000000000000001 t1 = 0000000000000000
t2 = 0000000000000180 t3 = 000000000009e000 t4 = fffffc00005d53c8
t5 = 0000000000003ff0 t6 = fffffc000068d100 t7 = fffffc0000540000
s0 = fffffc000060b880 s1 = fffffc0000564000 s2 = fffffc000060b7f0
s3 = fffffc000068c880 s4 = 0000000120001f40 s5 = 0000000000000000
s6 = 0000000000000000
a0 = fffffc0000564000 a1 = 0000000000000000 a2 = 0000000000000000
a3 = fffffc0000000008 a4 = 0000000000000000 a5 = 0000000000000000
t8 = 0000000000003fff t9 = fffffc00005d6540 t10= fffffc00005d5de0
t11= fffffc00005e0260 pv = fffffc00004d06e0 at = fffffc00005d54c8
gp = fffffc00005ba400 sp = fffffc0000543f70
Code: b53e0008 stq s0,8(sp)
203f0001 lda t0,1(zero)
b55e0010 stq s1,16(sp)
20d13ff0 lda t5,16368(a1)
b75e0000 stq ra,0(sp)
47f0040a or zero,a0,s1
*a6e20000 ldq t9,0(t1)
48255721 sll t0,42,t0
Trace:31001c
Kernel panic: Attempted to kill the idle task!
In idle task - not syncing

=== ksymoops output begin ===

ksymoops 2.4.1 on alpha 2.2.19pre16-smp. Options used
-V (default)
-K (specified)
-l /proc/modules (default)
-o /lib/modules/2.4.5-pre2aa1 (specified)
-m /boot/System.map-2.4.5pre2aa1 (specified)

No modules in ksyms, skipping objects
No ksyms, skipping lsmod
Unable to handle kernel paging request at virtual address 0000000000000000
CPU 0 swapper(0): Oops 0
pc = [<fffffc00004e44e8>] ra = [<fffffc00004e4c54>] ps = 0000
Using defaults from ksymoops -t elf64-alpha -a alpha
v0 = fffffc0000564000 t0 = 0000000000000001 t1 = 0000000000000000
t2 = 0000000000000180 t3 = 000000000009e000 t4 = fffffc00005d53c8
t5 = 0000000000003ff0 t6 = fffffc000068d100 t7 = fffffc0000540000
s0 = fffffc000060b880 s1 = fffffc0000564000 s2 = fffffc000060b7f0
s3 = fffffc000068c880 s4 = 0000000120001f40 s5 = 0000000000000000
s6 = 0000000000000000
a0 = fffffc0000564000 a1 = 0000000000000000 a2 = 0000000000000000
a3 = fffffc0000000008 a4 = 0000000000000000 a5 = 0000000000000000
t8 = 0000000000003fff t9 = fffffc00005d6540 t10= fffffc00005d5de0
t11= fffffc00005e0260 pv = fffffc00004d06e0 at = fffffc00005d54c8
gp = fffffc00005ba400 sp = fffffc0000543f70
Code: b53e0008 stq s0,8(sp)
203f0001 lda t0,1(zero)
b55e0010 stq s1,16(sp)
20d13ff0 lda t5,16368(a1)
b75e0000 stq ra,0(sp)
47f0040a or zero,a0,s1
48255721 sll t0,42,t0
Trace:31001c
Kernel panic: Attempted to kill the idle task!
Warning (Oops_read): Code line not seen, dumping what data is available
>>PC; fffffc00004e44e8 <secondary_cpu_start+28/1a0> <=====
Trace; 0031001c Before first symbol


1 warning issued. Results may not be reliable.





$ cat /proc/cpuinfo
cpu : Alpha
cpu model : EV67
cpu variation : 7
cpu revision : 0
cpu serial number :
system type : Tsunami
system variation : DP264
system revision : 0
system serial number :
cycle frequency [Hz] : 666666666
timer frequency [Hz] : 1024.00
page size [bytes] : 8192
phys. address bits : 44
max. addr. space # : 255
BogoMIPS : 1334.16
kernel unaligned acc : 0 (pc=0,va=0)
user unaligned acc : 0 (pc=0,va=0)
platform string : AlphaPC 264DP 666 MHz
cpus detected : 2
cpus active : 2
cpu active mask : 0000000000000003

--
Don't feed. DI Michael Wildpaner
Don't provoke. Ph.D. Student
Don't enter the cage.





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