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[MSP430] Fix passing C structs and unions as function arguments

Authored by atrosinenko on Aug 13 2020, 11:12 AM.



Pass structures, classes and unions by reference on MSP430, according to Section 3.5 of MSP430 EABI. The callee is responsible for leaving the underlying data intact.

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atrosinenko created this revision.Aug 13 2020, 11:12 AM
Herald added a project: Restricted Project. · View Herald TranscriptAug 13 2020, 11:12 AM
atrosinenko requested review of this revision.Aug 13 2020, 11:13 AM

Restore test formatting.

Harbormaster completed remote builds in B68299: Diff 285436.

Update with implicit pointers being passed through.

rjmccall accepted this revision.Aug 17 2020, 1:36 PM



Oh wow, the ABI really is indirect aliased:

To pass a structure or union by reference, the caller places its address
in the appropriate location: either in a register or on the stack, according
to its position in the argument list. To preserve pass-by-value semantics
(required for C and C++), the callee may need to make its own copy of the
pointed-to object. In some cases, the callee need not make a copy, such
as if the callee is a leaf and it does not modify the pointed-to object.

I didn't realize any actual ABIs did this.

This revision is now accepted and ready to land.Aug 17 2020, 1:36 PM