[ECOS] Main stack alignment

[Jonathan Larmour]

Daniel Lidsten wrote:
> Hi,
> 
> When i allocate two structures in the main loop then they will be place
> with an 8 bytes alignment in the main_stack. Why is that?
> 
> The stack is declared as:
> static cyg_uint8 cyg_libc_main_stack[
> CYGNUM_LIBC_MAIN_DEFAULT_STACK_SIZE ] in mainthread.cxx;
> 
> ...and placed in the .bss section by the linker script.
> 
> The odd thing is that if i declare my structures as static or make them
> global, then they are 2-byte aligned. How come? I want my structures to
> be 2 byte aligned even when i declare them inside main.

IIRC GCC often takes a pessimistic view of stack alignment and assumes it 
may not be well aligned and so aligns it itself.

For static/global stuff, the linker puts it at a well defined address and 
can therefore be sure of its address.

You may be able to override GCC's behaviour on the command line depending 
on your architecture.

Jifl
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