On 03/13/2012 09:37 PM, Linus Torvalds wrote: > On Tue, Mar 13, 2012 at 8:44 PM, Boaz Harrosh <bharrosh@xxxxxxxxxxx> wrote: >> Since then any use of "variable length arrays" has become blasphemous. >> Even in perfectly good, beautiful, perfectly safe code like the one >> below where the variable length arrays are only used as a sizeof() >> parameter, for type-safe dynamic structure allocations. GCC is not >> executing any stack allocation code. > > If it's a compile-time constant, just make it one. Stop the whining. > No VLA's required. You could, for example, make a trivial wrapper > macro that just declares that array as a constant array in the caller, > and it really *is* a constant sized array with no questions asked. > You have not read the code. I do not have a "constant sized array" I have a function that receives num_entries as parameter. In turn, the function declares an array *type* of variable size, just a type, not an actual array. Then uses that type as a sizeof() parameter to take the size and call kalloc for actual object allocation. So all I'm doing is using the compiler generated math to multiply the record size by num_entries. No other code is generated. The reason I like them a lot is because I'm now not doing any *casting* like I do with the new code. After I did the wrong math and stumped all over Kernel memory a couple of times I like the compiler to check me out. > Instead, you waste more time and effort *whining* than doing that > technical solution. > Well I also did the change which is not that bad. So since I sent in a fix, I'm entitled to a *whine*. Specially in light of the assembly proof I sent. Which you did not quote. > You do realize that VLA's have caused real problems, since you even > quote some of the background. Not to mention all the problems they > cause for semantics analysis and static checkers. > Sure, that's true > VLA's really aren't a very good thing in the kernel. And the > work-around I suggest above is actually *simpler* than using them and > then spednign the effort explaining "but they are actually constants > at compile time after all, and aren't the bad kinds of VLAs". > Again, I am actually using real VLAs but only as a type definition not as an object declaration. And that part works very well. (Again see assembler attached) > Just don't do them. They are a mistake. > Yes! So I've sent in a patch. Assembler wise it's identical. static checkers should now be happy. So here it is. Just that I don't have to like it or agree with you. > Linus Thanks for your reply, always a pleasure Boaz -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
