Re: CYG_HAL_TABLE_END alignment

[Peter Korsgaard <jacmet at sunsite dot dk>]

>>>>> "Bart" == Bart Veer <bartv@ecoscentric.com> writes:

 Bart>     struct fred { 
 Bart>      cyg_uint32 a; 
 Bart>      cyg_uint8 b[3];
 Bart>     }

 Bart> On most architectures the compiler and linker will arrange for
 Bart> the start of this structure to be aligned to a 4-byte boundary,
 Bart> i.e. a byte of padding gets inserted. When the compiler
 Bart> iterates through the table it thinks it has a fred[] array with
 Bart> each entry properly aligned. The linker does not see an array,
 Bart> it gets a number of individual variables, but it will align
 Bart> each one's start to the appropriate boundary. So no problems so
 Bart> far.

Yes, but the padding byte is "inside" the structure,
E.G. sizeof(struct fred) == 8 - isn't it?

 Bart> Linker alignment only applies to the start of a structure, not
 Bart> the end. Therefore when the linker places the end of the table
 Bart> label this would appear immediately after the last entry,
 Bart> without the padding.  That is a bad idea so the end is
 Bart> explicitly aligned in the code.

But immediately after the last entry is correct, as that is where the
next element would be placed.

To me the alignment directive should simply be removed from the
CYG_HAL_TABLE_END macro - or am I missing something?

 Bart> P.S. I'll take a look at your I2C patches when I get a chance,
 Bart> probably this weekend.

Thanks!

-- 
Bye, Peter Korsgaard