From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: [PATCH 6 of 8] Xen: remove run_in_exception_handler() and recode its only caller Date: Mon, 07 Mar 2011 15:44:51 +0000 Message-ID: References: <20110307153841.GA28479@whitby.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20110307153841.GA28479@whitby.uk.xensource.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Tim Deegan Cc: "xen-devel@lists.xensource.com" List-Id: xen-devel@lists.xenproject.org On 07/03/2011 15:38, "Tim Deegan" wrote: > At 15:15 +0000 on 07 Mar (1299510944), Keir Fraser wrote: >> On 07/03/2011 15:05, "Keir Fraser" wrote: >> >>> On 07/03/2011 11:26, "Tim Deegan" wrote: >>> >>>> (dump_execution_state()) as its own bug-trap. >>>> >>>> This is needed to compile xen with clang, which can't handle using a >>>> function name in an asm immediate. >>> >>> Actually run_in_exception_handler() does have another user, in ns16550.c. >>> Although non-essential, it makes the 'd' debug key much more useful when >>> running the UART in polled mode. >>> >>> So I suggest we keep run_in_exception_handler but modify it to pass the >>> function pointer in (say) rAX. >> >> Like the attached patch (against latest tip). > > Sorry, I had missed that other user. I'll see if I can find a way to > make clang use the function address directly; if not, I'd be inclined to > have dump_execution_state have its own ID anyway, to keep %rax valid(er) > in BUG()s. But actually dump_execution_state() isn't used for BUGs and WARNs and ASSERTs. In fact it's practically dead on x86 -- it's used in one rather unlikely ACPI error function, and also in __bug/__warn which are never used on x86. And that's it. Actually the user of run_in_exception_handler() in ns16550.c is really the only one we care about! -- Keir > Tim. > >>> I think we won't easily be able to use >>> BUG_STR() logic but r_i_e_h is only used (directly or indirectly) in a few >>> places so the BUG_STR optimisation is unimportant. The only other >>> disadvantage is that rAX is less interesting in the state dump, but any >>> value the function pointer displaces can still be found in the stack dump, >>> albeit with likely a little extra effort. >>> >>> Sound good? >>> >>> -- Keir >>> >>>> Signed-off-by: Tim Deegan >>>> >>>> >>>> _______________________________________________ >>>> Xen-devel mailing list >>>> Xen-devel@lists.xensource.com >>>> http://lists.xensource.com/xen-devel >>> >>> >> > >