On Thu, Jan 28, 2021 at 01:45:51PM -0800, Linus Torvalds wrote: > On Thu, Jan 28, 2021 at 1:34 PM Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote: > > > > On Thu, Jan 28, 2021 at 01:23:11PM -0800, Linus Torvalds wrote: > > > THAT workaround is long gone, but I didn't check what other ones we > > > might have now. But the gcc version checks we _do_ have are not > > > necessarily about major versions at all (ie I trivially found checks > > > for 4.9, 4.9.2, 5.1, 7.2 and 9.1). > > > > Then maybe the check should be same major.minor? > > Well, how many of them are actually about things that generate > incompatible object code? > > The main one I can think of is the KASAN ABI version checks, but > honestly, I think that's irrelevant. I really hope no distros enable > KASAN in user kernels. > > Another version check I looked at was the one that just checks whether > the compiler natively supports __builtin_mul_overflow() or not - it > doesn't generate incompatible object code, it just takes advantage of > a compiler feature if one exists. You can mix and match those kinds of > things well enough. > > So I'd really like to hear actual hard technical reasons with > examples, for why you'd want to add this test in the first place. Unfortunately I don't have technical reasons beyond what we've already discussed, found from code inspection. This patch was born from a discussion where wildly different opinions were expressed about whether such a mismatch scenario (or even external modules in general!) would be supported at all. So I guess the goal is to clarify (in the code base) to what extent compiler mismatches are supported/allowed/encouraged. Because they definitely happen in the real world, but a lot of people seem to be sticking their head in the sand about it. If we decide it's not a cut-and-dry makefile check, then the policy should at least be documented. I'd prefer the warning though, since nobody's going to read the docs. > No hand-waving "different compiler versions don't work together". > Because that's simply not true. > > > And convert it to a strongly worded warning/disclaimer? > > A warning might be better for the simple reason that it wouldn't cause > people to just fix it with "make oldconfig". > > Maybe you haven't looked at people who compile external modules, but > they always have various "this is how to work around issues with > version XYZ". That "make oldconfig" would simply just become the > workaround for any build errors. > > And a warning might be more palatable even if different compiler > version work fine together. Just a heads up on "it looks like you > might be mixing compiler versions" is a valid note, and isn't > necessarily wrong. Even when they work well together, maybe you want > to have people at least _aware_ of it. Sounds reasonable. -- Josh
