I recently had some problems dchar[] arr = [ ‘ ‘, TAB, CR, LF … ];
and I got errors from the compiler which led to me having to count the elements in the initialiser and declare the array with an explicit size. I don’t want the array to be mutable so I later added immutable to it, but that didn’t help matters. At one point, because the array was quite long, I got the arr[ n_elements ] number wrong, it was too small and the remainder of the array was full of 0xffs (or something), which was good, helped me spot the bug.
Is there any way to get the compiler to count the number of elements in the initialiser and set the array to that size ? And it’s immutable.
The only reason that I’m giving it a name is that I want the object to be used in several places and I don’t want multiple copies of it in the code/readonly initialised data segment.
Another couple of unrelated questions: is there such a thing as a no-execute initialised readonly data segment? I’m seeing immutables going into the code segment, I think, with x86 LDC at least, can’t remember about GDC. Anyway on x86-64 immutables are addressed as [rip + displ] which is very pleasing as it’s vastly more efficient than accessing statics in TLS which seems to be a nightmare in Linux at least.
In MS Windows, isn’t TLS dealt with using FS: ( or GS: ?) prefixes? Shame this doesn’t seem to be exploited in Linux, or am I wrong?
I’d like to deal with the overhead of retrieving the static base address all the time in the Linux situation (if I have got the right end of the stick) but having an ‘application object’ which contains all the statics in a struct in an alloc cell or something, and passing a pointer to this static base app object everywhere seems a nightmare too as it eats a register and worse eats one of the limited number of precious function argument registers which are in short supply in eg x86-64, where there are less than half a dozen argument registers allowed. I realise that one can deal with that limited number by rolling some passed arguments up into a passed struct, but that’s introducing a level of indirection and other overhead, that or just live with the fact that the extra args are going into the stack, which isn’t the worst thing in the world. I wonder what others do about statics in TLS?
