On 06-12-2012 19:28, Timo Sintonen wrote:
I have some memory mapped hardware in my arm controller. I define struct regs to describe the registers and __gshared regs* p to point to the actual address. I have a loop like: while (p.status==0) {...}The body of the loop does not touch status and so gdc optimizer does not evaluate status again, resulting to an endless loop. Gcc does the same, unless the variable is defined as volatile. This is ok in tls variables, but gshared variables are not thread safe. Actually I can see from assembler code that this occurs in all shared variables, like: __gshared int a=0; while (a==0) {} with nothing in the body generates just a jump to itself and the program stops. Another thread, interrupt or hardware can change a __gshared variable any time, so I think that the evalution should not be optimized away.
Yes, the compiler *must* assume that anything __gshared is implicitly volatile in the C sense.
Please file an issue: http://gdcproject.org/bugzilla/
Another related question: is there a way to make the pointer p immutable but leave the data mutable? The pointer is always set to the fixed address of the hardware, but making the pointer const makes also the data immutable.
Not with D's type system, since type qualifiers are transitive. -- Alex Rønne Petersen a...@lycus.org http://lycus.org
