Re: Problems migrating to gcc 4.4.3&eabi - apparently a gcc bug

[Thomas Martitz <thomas.martitz@student.HTW-Berlin.de>]

Am 09.03.2010 19:36, schrieb Andrew Haley:
> That does not surprise me.  I think you're seeing a problem that is
> caused by something elsewhere in your program.  I'm guessing that
> there may be a bad prototype or somesuch.
>
> I think you need to strip down your sources until you find something.
>
> Maybe you should try -save-temps and have a look at the actual
> preprocessd source.  Maybe some bastard has done
>
> #define int long
>
> or something evil like that!
>
> Andrew.
>    

No, I know our codebase pretty well. This is not the problem. Not that 
int or long matters, anyway.

In the mean time we found a test case:

----
void foo(int last, char * block);

void bar(void)
{
     struct {
         char * __attribute__((aligned(8))) member;
     } s;

     foo(0,s.member);
}
----

compiled with arm-elf-eabi-gcc -c test.c

This example exposes the problem.

We found the problem is related to struct addressing and the aligned 
attribute.

- normal stack variables work
- struct members work with __attribute__((aligned(4)))
- struct members with __attribute__((aligned(X))) where X >= 8 *do not* 
work.

Look at the assembly output for this very example. block is passed in 
r2, while it's supposed to be passed in r1.

Our temporary "fix" is to make it "void foo(int last, volatile char * 
block);" [notice the volatile keyword] and it works as well (block 
passed in r1).

This is definitely a gcc bug. The generated call is dependent on the 
parameter passed. The callee can't know about this. And it also happens 
with -O0.


Best regards.