Hello,
I'm running Linux on a LEON3 SparcV8 without floating point unit
present (the PSR_EF bit is hardwired to 0).
I noticed that I can easily cause a kernel panic by running a
user-mode application with an FPU instruction in it.
The FPU instruction traps to do_fpd_trap().
The kernel then tries to enable the FPU by setting PSR_EF and performs
an FPU context switch. During the FPU context switch, the kernel itself
executes an FPU instruction, which jumps to do_fpd_trap() and then the
system dies.
I prepared a patch which modifies do_fpd_trap() to be more graceful
on machines that can not enable PSR_EF.
Tested on Linux 3.7.1 and Linux 3.8-rc4.
Can anyone here decide if this is the right approach and help me to
get this fixed in the kernel?
Thanks, Joris.
diff -U 5 -urN linux-3.7.1/arch/sparc/kernel/traps_32.c linux-3.7.1-sparcfp/arch/sparc/kernel/traps_32.c
--- linux-3.7.1/arch/sparc/kernel/traps_32.c 2012-12-17 20:14:54.000000000 +0100
+++ linux-3.7.1-sparcfp/arch/sparc/kernel/traps_32.c 2013-01-20 19:38:02.616017770 +0100
@@ -183,10 +183,24 @@
/* Sanity check... */
if(psr & PSR_PS)
die_if_kernel("Kernel gets FloatingPenguinUnit disabled trap", regs);
put_psr(get_psr() | PSR_EF); /* Allow FPU ops. */
+
+ if ((get_psr() & PSR_EF) == 0) {
+ /* No FPU present. Do not kill the kernel in this case. */
+ siginfo_t info;
+ printk(KERN_INFO "%s[%d]: no FPU present PC=%08lx\n", current->comm, task_pid_nr(current), pc);
+ info.si_signo = SIGFPE;
+ info.si_errno = 0;
+ info.si_addr = (void __user *)pc;
+ info.si_trapno = 0;
+ info.si_code = __SI_FAULT;
+ force_sig_info(SIGFPE, &info, current);
+ return;
+ }
+
regs->psr |= PSR_EF;
#ifndef CONFIG_SMP
if(last_task_used_math == current)
return;
if(last_task_used_math) {
--
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