Hi, sir_richard wrote: > * We really have to get a good DS/ES first before touching any data. > * > * These two reads will either go in a register (with optimizations ON) or > * a stack variable (which is on SS:ESP, guaranteed to be good/valid). > * > * Because the assembly is marked volatile, the order of instructions is > * as-is, otherwise the optimizer could simply get rid of our DS/ES.
Timo Kreuzer wrote: > 2.) Segements should be fixed up before entering C code, as not doing so > may introduce possible compiler dependend breakages. It's also much > cleaner and there's no reason to do the same stuff later in inline assembly > instead of direcly in the asm entry point. Ros Arm wrote: > Regarding #2, I unfortunately do not see the need to add more assembly > when it is not needed. There are no subtle compiler breakages involved, > since it is impossible for the compiler to add a DS/ES access for no reason > at all (can you come up with an example?), this is part of the contract the > compiler has to make (if compilers did this, it would break a whole class of > embedded and real-mode software). Because the stack is safe, I think it's > worth avoiding the extra lines of assembly. The C inlines will produce > exactly the same code anyway. Not as a guide to action, simply to note — there is no guarantee that volatile asm statements (and code around them) will never be reordered. As only two registers are needed to keep Ds and Es, it seems to work there. But in a general case, GCC does not hesitate to rearrange such stuff… _______________________________________________ Ros-dev mailing list Ros-dev@reactos.org http://www.reactos.org/mailman/listinfo/ros-dev
