Serious Bug All Targets -- Please Read

Ralf Corsepius ralf.corsepius at
Tue Mar 3 03:09:01 UTC 2009

Till Straumann wrote:
> Ralf Corsepius wrote:
>> Till Straumann wrote:
>>> Hmm - AFAIK, c99 doesn't specify the exact representation
>>> of 'bool' / '_Bool'. It only says that
>>> "An object declared as type _Bool is large enough to store the 
>>> values 0 and 1"
>>> Hence, there is no really safe way to access such
>>> an object from assembly code.
>> Exactly.
>>> I wonder if it wouldn't be better to change the
>>> type of _Context_Switch_necessary & friends
>>> to a type of known width.
>> IMO, no.
>> We should change to code into something which doesn't need to know 
>> the size of a type, rsp. automatically gets it right.
> So how would you do that given the requirement
> that these variables need to be available to
> assembly code, maybe w/o a stack available?
E.g. by rewriting the code in question in C w/ inline asm. This isn't 
always possible, but is possible on many occasions, even when  stack is 
not available. It also somewhat (not always) helps to catch such size 
mismatches early.

Another possibility would be not to use _Bool for them (Which is the 
type GCC interally uses), but to use an "int" or a dedicated typedef to 
another size-expansion compatible type (I.e. any other ordinal type - 
_Bool is an ordinal type).


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