[cfe-dev] crash fix, need help

Sean Middleditch sean at awesomeplay.com
Sun Dec 9 13:14:25 PST 2007

Worked on tracking down the crash I have with my small test app, a.k.a.

The crash is actually a failed assertion at
RecordOrganizer::addPaddingFields, due to the RequiredBits not being a
multiple of 8.

The struct in question is struct _win_st from ncurses.h, and the field
causing this is _clear, which is of type _Bool, and immediately followed
another _Bool, _notimeout.  These are the first two _Bool types in the

The alignment is off by a single bit.  I'm figuring what is happening is
that the first _Bool is being added as a single bit field to the struct,
and then the second _Bool is trying to add padding and failing because
the addPaddingFields method can only add padding with bits in multiples
of 8.

What I'm wondering is what the proper fix is.  Either _Bool should be an
8-bit type, or addPaddingFields needs to be able to pad by arbitrary
bits _and_ two (or more) consecutive _Bool types should not be forcing
extra padding.  (It seems that _Bool wants 32-bit alignment, for that
matter, or I'm just failing to understand the meaning of the
AlignmentInBits calculated in addLLVMField.)

Once that's figured out, of course, I need to determine how to actually
do either of those.  :)

By the way, I must say, given its size and the complexity of its subject
material, the clang code is really quite readable.  In my line of work,
I run into small 30 line barely-functional scripts that are harder to
grok than clang.  This is great work!

- Sean

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