signal/powerpc: Replace TRAP_FIXME with TRAP_UNK

Using an si_code of 0 that aliases with SI_USER is clearly the wrong
thing todo, and causes problems in interesting ways.

For use in unknown_exception the recently defined TRAP_UNK
semantically is a perfect fit. For use in RunModeException it looks
like something more specific than TRAP_UNK could be used. No one has
bothered to find a better fit than the broken si_code of 0 in all of
these years and I don't see an obvious better fit so TRAP_UNK is
switching RunModeException to return TRAP_UNK is clearly an
improvement.

Recent history suggests no actually cares about crazy corner
cases of the kernel behavior like this so I don't expect any
regressions from changing this. However if something does
happen this change is easy to revert.

Though I wonder if SIGKILL might not be a better fit.

Cc: Paul Mackerras <[e-mail]>
Cc: Kumar Gala <[e-mail]>
Cc: Michael Ellerman <[e-mail]>
Cc: Benjamin Herrenschmidt <[e-mail]>
Cc: [e-mail]
Fixes: 9bad068c24d7 ("[PATCH] ppc32: support for e500 and 85xx")
Fixes: 0ed70f6105ef ("PPC32: Provide proper siginfo information on various exceptions.")
History Tree: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
Signed-off-by: "Eric W. Biederman" <[e-mail]>

arch/powerpc/include/uapi/asm/siginfo.h

···
 
 #include <asm-generic/siginfo.h>
 
-/*
- * SIGTRAP si_codes
- */
-#ifdef __KERNEL__
-#define TRAP_FIXME	0	/* Broken dup of SI_USER */
-#endif /* __KERNEL__ */
-
-
 #endif	/* _ASM_POWERPC_SIGINFO_H */

arch/powerpc/kernel/traps.c

···
 	printk("Bad trap at PC: %lx, SR: %lx, vector=%lx\n",
 	       regs->nip, regs->msr, regs->trap);
 
-	_exception(SIGTRAP, regs, TRAP_FIXME, 0);
+	_exception(SIGTRAP, regs, TRAP_UNK, 0);
 
 	exception_exit(prev_state);
 }
···
 
 void RunModeException(struct pt_regs *regs)
 {
-	_exception(SIGTRAP, regs, TRAP_FIXME, 0);
+	_exception(SIGTRAP, regs, TRAP_UNK, 0);
 }
 
 void single_step_exception(struct pt_regs *regs)