From mboxrd@z Thu Jan  1 00:00:00 1970
From: Helge Deller <deller-Mmb7MZpHnFY@public.gmane.org>
Subject: Re: [PATCH 1/8] signal/alpha: Document a conflict with SI_USER for
	SIGTRAP
Date: Sun, 2 Jul 2017 16:13:20 +0200
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To: "Eric W. Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
Cc: Andrei Vagin <avagin-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org>, Greg KH <greg-U8xfFu+wG4EAvxtiuMwx3w@public.gmane.org>, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Pavel Emelyanov <xemul-5HdwGun5lf+gSpxsJD1C4w@public.gmane.org>, linux-arch-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Matt Turner <mattst88-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Ivan Kokshaysky <ink-biIs/Y0ymYJMZLIVYojuPNP0rXTJTi09@public.gmane.org>, Al Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>, Andy Lutomirski <luto-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Cyrill Gorcunov <gorcunov-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>, Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>, Richard Henderson <rth-hL46jP5Bxq7R7s880joybQ@public.gmane.org>, Andrey Vagin <avagin-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Linux Containers <containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>, Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, linux-alpha-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Linus Torvalds <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Willy Tarreau <w@1wt.eu>
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* Eric W. Biederman <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>:
> Setting si_code to __SI_FAULT 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.
> 
> Given that alpha is on it's last legs I don't know that it is worth
> fixing this, but it is worth documenting what is going on so that
> no one decides to copy this bad decision.

The ABI was already broken, so IMHO I think it's better to somehow "fix"
it instead. Agreed, alpha and some other architectures are already aged,
but nevertheless most of them build in debian-ports.  Below is a
suggested fix which reuses/misuses other existing trap codes instead.

Helge

Signed-off-by: Helge Deller <deller-Mmb7MZpHnFY@public.gmane.org>

diff --git a/arch/alpha/kernel/traps.c b/arch/alpha/kernel/traps.c
index 65bb102..2ed37dd 100644
--- a/arch/alpha/kernel/traps.c
+++ b/arch/alpha/kernel/traps.c
@@ -278,7 +278,7 @@ do_entIF(unsigned long type, struct pt_regs *regs)
 	      case 1: /* bugcheck */
 		info.si_signo = SIGTRAP;
 		info.si_errno = 0;
-		info.si_code = __SI_FAULT;
+		info.si_code = TRAP_HWBKPT;
 		info.si_addr = (void __user *) regs->pc;
 		info.si_trapno = 0;
 		send_sig_info(SIGTRAP, &info, current);
@@ -318,7 +318,7 @@ do_entIF(unsigned long type, struct pt_regs *regs)
 			break;
 		case GEN_ROPRAND:
 			signo = SIGFPE;
-			code = __SI_FAULT;
+			code = FPE_FLTSUB;
 			break;
 
 		case GEN_DECOVF:
@@ -340,7 +340,7 @@ do_entIF(unsigned long type, struct pt_regs *regs)
 		case GEN_SUBRNG7:
 		default:
 			signo = SIGTRAP;
-			code = __SI_FAULT;
+			code = TRAP_HWBKPT;
 			break;
 		}