On 03/09/2010 06:54 PM, Thomas Martitz wrote:
> 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.
Yeah, it's a bug. Mind you, it's pretty bizarre code: I'm not surprised
we never came across this before.
Why are you doing this, anyway? I would have expected
char __attribute__((aligned(8))) *member;
for a pointer to an 8-aligned buffer...
Andrew.
