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SubjectRe: [PATCH 04/11] signal/parisc: Document a conflict with SI_USER with SIGFPE
* Eric W. Biederman <>:
> Setting si_code to 0 results in a userspace seeing an si_code of 0.
> This is the same si_code as SI_USER. Posix and common sense requires
> that SI_USER not be a signal specific si_code. As such this use of 0
> for the si_code is a pretty horribly broken ABI.
> Further use of si_code == 0 guaranteed that copy_siginfo_to_user saw a
> value of __SI_KILL and now sees a value of SIL_KILL with the result
> that uid and pid fields are copied and which might copying the si_addr
> field by accident but certainly not by design. Making this a very
> flakey implementation.
> Utilizing FPE_FIXME siginfo_layout will now return SIL_FAULT and the
> appropriate fields will reliably be copied.
> This bug is 13 years old and parsic machines are no longer being built
> so I don't know if it possible or worth fixing it. But it is at least
> worth documenting this so other architectures don't make the same
> mistake.

I think we should fix it, even if we now break the ABI.

It's about a "conditional trap" which needs to be handled by userspace.
I doubt there is any Linux code out which is utilizing this
parisc-specific trap.

I'd suggest to add a new FPE trap si_code (e.g. FPE_CONDTRAP).
While at it, maybe we should include the already existing FPE_MDAOVF
from the frv architecture, so that arch/frv/include/uapi/asm/siginfo.h
can go completely.

Suggested patch is below.

I'm willing to test the patch below on the parisc architecture for a few
weeks. And it will break arch/x86/kernel/signal_compat.c which needs
looking at then too.



[PATCH] parisc: Add FPE_CONDTRAP for conditional trap handling

Posix and common sense requires that SI_USER not be a signal specific
si_code. Thus add a new FPE_CONDTRAP si_code for conditional traps.

Signed-off-by: Helge Deller <>

diff --git a/arch/parisc/kernel/traps.c b/arch/parisc/kernel/traps.c
index 8453724b8009..13702f0f5ba1 100644
--- a/arch/parisc/kernel/traps.c
+++ b/arch/parisc/kernel/traps.c
@@ -627,9 +627,9 @@ void notrace handle_interruption(int code, struct pt_regs *regs)
on condition */
si.si_signo = SIGFPE;
- /* Set to zero, and let the userspace app figure it out from
- the insn pointed to by si_addr */
- si.si_code = 0;
+ /* Let userspace app figure out from the insn pointed
+ * to by si_addr */
+ si.si_code = FPE_CONDTRAP;
si.si_addr = (void __user *) regs->iaoq[0];
force_sig_info(SIGFPE, &si, current);
diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
index e447283b8f52..2b759fe42142 100644
--- a/include/uapi/asm-generic/siginfo.h
+++ b/include/uapi/asm-generic/siginfo.h
@@ -193,7 +193,9 @@ typedef struct siginfo {
#define FPE_FLTRES 6 /* floating point inexact result */
#define FPE_FLTINV 7 /* floating point invalid operation */
#define FPE_FLTSUB 8 /* subscript out of range */
-#define NSIGFPE 8
+#define FPE_MDAOVF 9 /* media overflow */
+#define FPE_CONDTRAP 10 /* trap on condition */
+#define NSIGFPE 10

* SIGSEGV si_codes
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