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