Re: gnat compiler issues with a partial build

[rrr.eee.27@gmail.com]

On Thursday, June 4, 2015 at 1:12:27 PM UTC+2, jan.de...@gmail.com wrote:
> First the good news: I was able to load and unload a mixed C and Ada kernel module last night for the first time.
> 
> But I think I found a subtle problem in the compiler (gnat-gcc 4.7.4) while doing my Linux kernel module.
> 

> -------------------------------------
> jan@janDell:~/MMS/programs-KERNEL/ec-master/obj$ nm memory_copy.o
>                  U __gnat_rcheck_CE_Access_Check
> 0000000000000000 T memcpy
> 0000000000000000 D memory_copy_E
> -------------------------------------
> 
> They are all related to the Exception machinery and refer to about 4 or 5 symbols in "Ada.Exeptions" in the standard "x86 Linux" runtime.
> They are caused by any construct where the compiler suspects that there might be a runtime error under certain conditions. And they have to do with exception propagation I suspect, from looking at a disassembly.

> The bottom line is that, no-matter what I all switch off, the compiler sometimes emits random subroutine calls in its error detection section. Normally they don't bite you, because you would almost never hit them in a well constructed program. But a kernel module with those simply will not load; end.
> 
> The only vague reference to such a scenario might be in the "-gnatp" description in the gnat_ug.
> 
> So if any of the compiler theologians has any light on this: please feel welcome to comment.


The symbol shown (__gnat_rcheck_CE_*) is generated for language required run time checks. Here it is an access check. They typically are range checks.

These checks are generated if you don't suppress them via -gnatp regardless of the capabilities of the RTS. Your coding style and the compiler switches must match the RTS capabilities. You don't suppress the run time checks by a pragma Restriction only, you also have to set the command line option -gnatp.

In another post you said that you don't wanted to use -gnatp as that would be like coding in C. That is not my experience at all!  The compiler still does a fantastic job at compile time to ensure range and access properties. Gnat found quite some subtle errors in my code even with checks suppressed (-gnatp).

RE