Greetings, and thanks so much for this and the kernel fix!
I've committed a little test which hopefully will enable trapping
these signals when the kernel fix is in place:
--- o/sgbc.c 1 Oct 2010 19:15:40 -0000 1.9.4.1.2.12.6.1.2.1.6.4
+++ o/sgbc.c 25 Oct 2010 19:46:35 -0000
@@ -1146,10 +1146,6 @@
memset(b1,32,2*p);
memset(b2,0,p);
memprotect_test_address=(void *)(((unsigned long)b1+p-1) & ~(p-1));
- if (mprotect(memprotect_test_address,p,PROT_READ_EXEC)) {
- memprotect_result=memprotect_cannot_protect;
- return -1;
- }
sa.sa_sigaction=(void *)memprotect_handler_test;
sa.sa_flags=MPROTECT_ACTION_FLAGS;
if (sigaction(SIGSEGV,&sa,&sao)) {
@@ -1161,6 +1157,29 @@
memprotect_result=memprotect_sigaction;
return -1;
}
+ { /* mips kernel bug test -- SIGBUS with no faddr when floating point is emulated. */
+ float *f1=(void *)memprotect_test_address,*f2=(void *)b2;
+
+ if (mprotect(memprotect_test_address,p,PROT_READ_EXEC)) {
+ memprotect_result=memprotect_cannot_protect;
+ return -1;
+ }
+ memprotect_result=memprotect_bad_return;
+ *f1=*f2;
+ if (memprotect_result==memprotect_bad_return)
+ memprotect_result=memprotect_no_signal;
+ if (memprotect_result!=memprotect_none) {
+ sigaction(SIGSEGV,&sao,NULL);
+ sigaction(SIGBUS,&saob,NULL);
+ return -1;
+ }
+ memprotect_handler_invocations=0;
+
+ }
+ if (mprotect(memprotect_test_address,p,PROT_READ_EXEC)) {
+ memprotect_result=memprotect_cannot_protect;
+ return -1;
+ }
memprotect_result=memprotect_bad_return;
memset(memprotect_test_address,0,p);
if (memprotect_result==memprotect_bad_return)
This seems to work, but if you see any shortcomings, please let me
know.
Thanks so much again!
David Daney <ddaney@xxxxxxxxxxxxxxxxxx> writes:
> On 10/21/2010 09:19 AM, David Daney wrote:
>> On 10/20/2010 02:31 PM, Camm Maguire wrote:
>>> Greetings!
>>>
>>> Does this suffice?
>>>
>>> (sid)camm@gabrielli:~/maxima-5.22.1/tests$ uname -a
>>> Linux gabrielli 2.6.35.4-dsa-octeon #1 SMP Fri Sep 17 21:15:34 UTC
>>> 2010 mips64 GNU/Linux
>>> (sid)camm@gabrielli:~/maxima-5.22.1/tests$ cat /proc/cpuinfo
>>> system type : CUST_WSX16 (CN3860p3.X-500-EXP)
>>> processor : 0
>>> cpu model : Cavium Octeon V0.3
>> [...]
>>
>> Hah! I have those things piled up all around me.
>>
>> No guarantees, but I will try to reproduce it. If I can reproduce it, it
>> should be easy to fix.
>>
>
> Definitely a kernel bug. Consider this program:
>
> ------------8<--------sigbus.c-------
> #include <stdio.h>
> #include <stdlib.h>
> #include <unistd.h>
>
> #include <sys/mman.h>
>
> int main(int argc, char *argv[])
> {
> int pgsize;
> float *p1;
> float *p2;
> int r;
>
> pgsize = getpagesize();
>
> p1 = mmap(NULL, pgsize, PROT_READ | PROT_WRITE,
> MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>
> if (p1 == MAP_FAILED) {
> perror("mmap p1 failed");
> exit(1);
> }
>
> p2 = mmap(NULL, pgsize, PROT_READ | PROT_WRITE,
> MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>
> if (p2 == MAP_FAILED) {
> perror("mmap p2 failed");
> exit(1);
> }
>
> *p1 = 2.5;
> *p2 = 3.5;
>
> r = mprotect(p1, pgsize, PROT_READ);
> if (r) {
> perror("mprotect p1 failed");
> exit(1);
> }
>
> r = mprotect(p2, pgsize, PROT_READ);
> if (r) {
> perror("mprotect p2 failed");
> exit(1);
> }
>
> *p2 = *p1;
>
> asm volatile("" ::: "memory");
>
> puts("All done!");
>
> exit(0);
> }
> ------------8<-----------------------
>
> $ mips64-octeon-linux-gnu-gcc -Wall -mhard-float -march=mips64 -O3 -o
> sigbus sigbus.c
> $ mips64-octeon-linux-gnu-objdump -d sigbus > sigbus.dis
>
> The float copy '*p2 = *p1;' dissassembles as:
>
> 120000b30: c6400000 lwc1 $f0,0(s2)
> 120000b34: e6000000 swc1 $f0,0(s0)
>
> When run on an FPU-less system I get:
>
> ~ # ./sigbus
> Bus error
>
> When run on my x86_64 workstation:
>
> $ ./sigbus
> Segmentation fault (core dumped)
>
> I will fix this kernel bug.
>
> David Daney
>
>
>
>
--
Camm Maguire camm@xxxxxxxxxxxxxxxxx
==========================================================================
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