In order to fix issue #9401 the compiler was changed to add a padding
byte to any non-empty Go struct that ends in a zero-sized field. That
causes the Go version of such a C struct to have a different size than
the C struct, which can considerable confusion. Change cgo so that it
discards any such zero-sized fields, so that the Go and C structs are
the same size.
This is a change from previous releases, in that it used to be
possible to refer to a zero-sized trailing field (by taking its
address), and with this change it no longer is. That is unfortunate,
but something has to change. It seems better to visibly break
programs that do this rather than to silently break programs that rely
on the struct sizes being the same.
Update #9401.
Fixes#11925.
Change-Id: I3fba3f02f11265b3c41d68616f79dedb05b81225
Reviewed-on: https://go-review.googlesource.com/12864
Reviewed-by: Russ Cox <rsc@golang.org>
Clang 3.2 and older (as shipped with OS X Mountain Lion and older)
outputs ambiguous DWARF debug info that makes it impossible for us to
reconstruct accurate type information as required for this test.
Fixes#8611.
LGTM=rsc
R=r, rsc, minux
CC=golang-codereviews
https://golang.org/cl/135990043
In cgo, now that recursive calls to typeConv.Type() always work,
we can more robustly calculate the array sizes based on the size
of our element type.
Also, in debug/dwarf, the decision to call zeroType is made
based on a type's usage within a particular struct, but dwarf.Type
values are cached in typeCache, so the modification might affect
uses of the type in other structs. Current compilers don't appear
to share DWARF type entries for "[]foo" and "[0]foo", but they also
don't consistently share type entries in other cases. Arguably
modifying the types is an improvement in some cases, but varying
translated types according to compiler whims seems like a bad idea.
Lastly, also in debug/dwarf, zeroType only needs to rewrite the
top-level dimension, and only if the rest of the array size is
non-zero.
Fixes#8428.
LGTM=iant
R=iant
CC=golang-codereviews
https://golang.org/cl/127980043
