To: linux-kernel@vger.kernel.org
Cc: gcc@gcc.gnu.org, linuxppc-dev@lists.linuxppc.org
Subject: [PATCH] C undefined behavior fix
From: Momchil Velikov <velco@fadata.bg>
Date: 02 Jan 2002 01:03:25 +0200
Message-ID: <87g05py8qq.fsf@fadata.bg>
Lines: 36
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Sender: linux-kernel-owner@vger.kernel.org

[Cc: to gcc list, in case someone wants to argue about standards]

The appended patch fix incorrect code, which interferes badly with
optimizations in GCC 3.0.4 and GCC 3.1.

The GCC tries to replace the strcpy from a constant string source with
a memcpy, since the length is know at compile time.

Thus 
   strcpy (dst, "abcdef" + 2)
gives
   memcpy (dst, "abcdef" + 2, 5)

However, GCC does not handle the case, when the above offset (2) is
not within the bounds of the string, which result in undefined
behavior according to ANSI/ISO C99.

The error is that
   strcpy (namep, "linux,phandle" + 0xc0000000);
gets emitted as
   memcpy (namep, "linux,phandle" + 0xc0000000, 14 - 0xc0000000);

Regards,
-velco

--- 1.3/arch/ppc/kernel/prom.c	Wed Dec 26 18:27:54 2001
+++ edited/arch/ppc/kernel/prom.c	Tue Jan  1 22:53:23 2002
@@ -997,7 +997,7 @@
 		prev_propp = &pp->next;
 		namep = (char *) (pp + 1);
 		pp->name = PTRUNRELOC(namep);
-		strcpy(namep, RELOC("linux,phandle"));
+		memcpy (namep, RELOC("linux,phandle"), sizeof("linux,phandle"));
 		mem_start = ALIGN((unsigned long)namep + strlen(namep) + 1);
 		pp->value = (unsigned char *) PTRUNRELOC(&np->node);
 		pp->length = sizeof(np->node);
-
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