Serious Bug All Targets -- Please Read

Ralf Corsepius ralf.corsepius at
Tue Mar 3 08:26:58 UTC 2009

Till Straumann wrote:
> Ralf Corsepius wrote:
>> 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
> That's what the new PPC framework does.
>> w/ inline asm. This isn't always possible, but is possible on many 
>> occasions, even when  stack is not available.
> w/o stack I'm not sure...
You can do something like this (Pseudo-C code):

extern bool var;

int _foo_stub(....)
   asm( ENTRY_SYMBOL(foo) );
   asm( PROCESS(var) );

   asm( RETURN );

I.e. to use a C-function wrapper/stub and insert asm-functions inside of 
this function. It's a dirty hack, but it works quite well.

A real world example based on this approach in RTEMS can be found in 

>> 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"
> Well - that's what I originally proposed (int32_t actually).
> IMO changing the type of these critical variables from bool -> int32_t
> is least intrusive and probably the best solution for a 4.9.2
> release.
The problem with this is: Some rtems < 4.9 targets have used short 
(16bit) booleans.


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