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Re: [PATCH 0/3] Support for x86 segments as address classes
- From: Richard Henderson <rth at redhat dot com>
- To: Pedro Alves <palves at redhat dot com>, gdb-patches at gcc dot gnu dot org
- Date: Thu, 5 Nov 2015 15:15:09 +0100
- Subject: Re: [PATCH 0/3] Support for x86 segments as address classes
- Authentication-results: sourceware.org; auth=none
- References: <1446558190-13482-1-git-send-email-rth at redhat dot com> <563B3BA3 dot 3070402 at redhat dot com>
On 11/05/2015 12:21 PM, Pedro Alves wrote:
On 11/03/2015 01:43 PM, Richard Henderson wrote:
Which begs the question of whether I've simply missed
something in how to get hold of the current regcache?
get_current_frame / get_current_regcache ? If you can pass it down
through a couple layers, it's of course better.
Duh, get_current_regcache, of course. Thanks.
Which makes for a relatively easy patch to finish the support.
However, IMO the results aren't ideal. Consider:
int __seg_fs *f = (int __seg_fs *)16;
int __seg_gs *g = (int __seg_gs *)16;
return *f + *g;
Now, this really isn't a proper executable testcase, because I haven't set up
gs_base, but since libc.so set up fs_base for the thread pointer, it's good
enough to step into test() and examine some variables.
Breakpoint 2, test () at z.c:10
10 return *f + *g;
(gdb) ptype f
type = int * @__seg_fs
(gdb) ptype g
type = int * @__seg_gs
(gdb) info loc
f = 0x7ffff7fd9710
g = 0x10
It seems to me that the "real" value of both f and g are 0x10. Instead, we
display the converted value, displaying f with a surprising value.
It seems to me that it would be better to do the conversion when we want to
dereference, such as "print *f", but not otherwise. However, I'm not really
sure how that would interact with the other users of address classes throughout