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Message-ID: <4723DDDD.8050900@zytor.com>
Date: Sat, 27 Oct 2007 17:54:53 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: linux-arch@...r.kernel.org
CC: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: struct user . u_ar0
I recently noticed that all architectures appear to have an entry n
struct user called u_ar0:
struct user_pt_regs * u_ar0; /* Used by gdb to help find the values
for */
/* the registers. */
In all cases, u_ar0 is a pointer type, although the type of pointer
varies with the architecture.
However, under no conditions does this field ever contain a pointer
value! It is set by the a.out code and its derivatives as an offset,
not a pointer value (there are a total of four references in the kernel,
in arch/{m68k,blackfin}/kernel/process.c, arch/x86/ia32/ia32_aout.c and
fs/binfmt_aout.c -- they are all functionally identical and write-only):
dump.u_ar0 = (void *)(((unsigned long)(&dump.regs)) - ((unsigned
long)(&dump)));
Any reason to *NOT* change this field to "unsigned long"? <asm/user.h>,
where struct user is defined, is not exported to userspace in any
architecture as far as I can tell, although <linux/user.h>, which just
contains #include <asm/user.h>, *is* exported (clearly a bug.)
-hpa
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