From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marek Vasut Date: Tue, 20 Mar 2012 10:09:43 +0100 Subject: [U-Boot] [PATCH V2] i.MX28: Drop __naked function from spl_mem_init In-Reply-To: <20120320083929.94A98202A50@gemini.denx.de> References: <4F683862.4030709@denx.de> <20120320083929.94A98202A50@gemini.denx.de> Message-ID: <201203201009.43717.marex@denx.de> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de Dear Wolfgang Denk, > Dear Stefano, > > In message <4F683862.4030709@denx.de> you wrote: > > > + /* The following is "subs pc, r14, #4", used as return from DABT. */ > > > + const uint32_t data_abort_memdetect_handler = 0xe25ef004; > > ... > > > Are we maybe becoming warning addicted ? I know the reason for this (GCC > > raises a warning "-fstack-usage not supported for this target"), you > > have already asked the gcc people about this issue, and I do not have an > > idea how to fix this warning in a different way as you did. This is a > > sort of self-modifying code. > > In which way is this self-modifying code? I don't think so. Because it rewrites piece of RAM, which is then called in the Data abort context. > > > However, the original code is quite easy to understand - I cannot say > > the same after the patch, we rely on the comment to understand something. > > That's what comments are made for :-) > > > Should we really fix such as warnings even if we generate some obscured > > code ? Wolfgang, what do you think about ? > > Yes, we should fix warnings. If you run a MAKEALL and can be sure > that any message printed is a new problem you will not miss it, and > act as needed. If youy know that a build will pop up a number or > warnings, it's all too easy to miss if there is a new one - and > checking takes much more concentration. This is to be avoided. > > On the other hand, I agree that we should avoid obscure code as > well. But then, to me the assembler code "subs pc, r14, #4" is > already obscure enough - I have to admit that I don't really grok it, > nor why this needs to be a __naked function. What it does: return from abort mode back from where it was aborted, one instruction further. Why is it naked: Because you don't want to generate prelude etc. only the real contents of the function. That gives exactly 4 bytes. And that's what is used to rewrite the DABT handler. > > My understanding is that to avoid the warning we can either use this > "pre-compiled constant instruction" trick, or we would have to create > a new assembler source file for this single instruction function. Or put it into start.S > > When Marek and I discussed this, the constant seemed to be the > simplest approach (not the nicest, though). Ack > > If you don't like it, then we I think we will end up with a new tiny > assembler source file. Would that be preferred by you? > > Best regards, > > Wolfgang Denk Best regards, Marek Vasut