On 03/03/2021 17:04, Gedare Bloom wrote:
+#if CPU_STACK_ALIGNMENT > CPU_HEAP_ALIGNMENT
+ stack_align = CPU_STACK_ALIGNMENT;
+ stack_begin = (char *) RTEMS_ALIGN_UP( (uintptr_t) stack_begin, stack_align
);
+ stack_end = (char *) RTEMS_ALIGN_DOWN( (uintptr_t) stack_end, stack_align );
Why align down here? Why align the end at all?
Most stacks grow down, so the alignment of the end address is important.
Is there a requirement
for the stack area to be a multiple of the stack alignment? I guess we
can lose some bytes and return less than config->stack_size as a
result of this?
The CPU_STACK_ALIGNMENT should be set to the stack alignment required by
the ABI (in SMP configurations, it should be probably at least cache
aligned, but this is another topic). In this case all stack frames will
be on such a boundary and you can't use these extra bytes. Independent
of this, you should probably not calculate your stack size so that you
actually use the last byte of your stack.
Also the changed _Stack_Extend_size() includes the alignment overhead.
Shouldn't we better do...
#if CPU_STACK_ALIGNMENT > CPU_HEAP_ALIGNMENT
+ stack_align = CPU_STACK_ALIGNMENT;
+ stack_begin = (char *) RTEMS_ALIGN_UP( (uintptr_t) config->stack_area,
stack_align );
#else
stack_begin = config->stack_area;
No, I think the code in the patch is fine, however, I will add an assert
after the block to ensure that begin and end are aligned.
#endif
stack_end = stack_begin + config->stack_size;
So we always return the requested stack size?
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