[coLinux-users] A fix for the SIGFPE problem (>20040622)

[Dan A. <da...@co...>]

Hello,

Thanks to Joe I was able to reproduce the problem locally and worked
on a fix which makes the problem disappear.

For the technical aspect: Since until now none of the code in 
arch/i386/kernel/head.S actually runs when coLinux starts I've suspected
that there could be some initialization problem - if the kernel is not 
precisely aware of the CPU's capabilities and decides not to save the 
MMX registers between context switches it can indeed cause a problem. In 
a multi-process scenario (such as the one with gdb and Joe's program) the 
problem was indeed triggered before.

I've already commited the patch into the monotone server. If you can
check that firefox / xdvi aren't crashing anymore I'd be glad.



diff -u b/arch/i386/kernel/cooperative.c b/arch/i386/kernel/cooperative.c
--- b/arch/i386/kernel/cooperative.c
+++ b/arch/i386/kernel/cooperative.c
@@ -85,6 +85,15 @@
 	__asm__ __volatile__("movl %%cr4, %0" : "=r" (mmu_cr4_features));
 }
 
+asm(
+	""
+	".section .text\n"
+	".globl co_arch_start_kernel\n"
+	"co_arch_start_kernel:\n"
+	"       call co_startup_entry\n"
+	".previous\n"
+	"");
+
 void co_start_arch(void)
 {
 	co_early_cpu_init();
diff -u b/arch/i386/kernel/head.S b/arch/i386/kernel/head.S
--- b/arch/i386/kernel/head.S
+++ b/arch/i386/kernel/head.S
@@ -238,6 +238,7 @@
 	rep
 	movsl
 1:
+ENTRY(co_startup_entry)
 checkCPUtype:
 
 	movl $-1,X86_CPUID		#  -1 for no CPUID initially
diff -u b/include/linux/cooperative_internal.h b/include/linux/cooperative_internal.h
--- b/include/linux/cooperative_internal.h
+++ b/include/linux/cooperative_internal.h
@@ -28,6 +28,7 @@
 extern void co_idle_processor(void);
 extern void co_terminate(co_termination_reason_t reason);
 extern void co_start_kernel(void);
+extern void co_arch_start_kernel(void);
 extern void co_handle_jiffies(long count);
 
 extern void co_send_message(co_module_t from, 
diff -u b/kernel/cooperative.c b/kernel/cooperative.c
--- b/kernel/cooperative.c
+++ b/kernel/cooperative.c
@@ -48,8 +48,9 @@
         memcpy(co_boot_parameters, &co_passage_page->params[10], 
                sizeof(co_boot_parameters));
 
-	start_kernel();
+	co_arch_start_kernel();
 
+	/* should never be reached */
 	co_terminate(CO_TERMINATE_END);
 }
 



-- 
Dan Aloni
da...@co...