From: Chen Gang <xili_gchen_5257@hotmail.com>
To: Bernd Schmidt <bschmidt@redhat.com>, Mike Stump <mikestump@comcast.net>
Cc: Jeff Law <law@redhat.com>, Richard Henderson <rth@redhat.com>,
"Joseph S. Myers" <joseph@codesourcery.com>,
gcc-patches List <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH] gcc/ira.c: Check !HAVE_FP_INSTEAD_INSNS when frame pointer is needed and as global register
Date: Tue, 13 Oct 2015 15:10:00 -0000 [thread overview]
Message-ID: <BLU436-SMTP237194271F36D4F69C08BFAB9300@phx.gbl> (raw)
In-Reply-To: <561D1B80.8050706@redhat.com>
On 10/13/15 22:56, Bernd Schmidt wrote:
> On 10/13/2015 04:50 PM, Chen Gang wrote:
>> OK, under the bugzilla, the maintainer treated it as expected behavior
>> (not a bug). For me, we need more explanation for it (why we treat it
>> as expected behavior).
>
> A global register is under control of the user. If the compiler uses it as a frame pointer, it will get clobbered outside the user's control, which is unexpected behaviour. Therefore, the code Mike quoted detects that case and issues an error, indicating that you must use -fomit-frame-pointer if you expect to use the frame pointer register for other purposes.
>
OK, thanks.
> If you want an address on the stack there's __builtin_frame_address which may or may not do what was intended. The code quoted in the bugzilla is just invalid.
>
OK, thank you very much, I shall send related kernel fix patch to kernel
mailing list.
Thanks.
--
Chen Gang (陈刚)
Open, share, and attitude like air, water, and life which God blessed
prev parent reply other threads:[~2015-10-13 15:10 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <561A7D5C.40409@hotmail.com>
2015-10-11 15:16 ` Chen Gang
2015-10-12 10:49 ` Bernd Schmidt
2015-10-12 22:30 ` Chen Gang
2015-10-12 23:03 ` Mike Stump
2015-10-13 14:48 ` Chen Gang
2015-10-13 14:56 ` Bernd Schmidt
2015-10-13 15:10 ` Chen Gang [this message]
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