Hi. 2018-07-10 11:29 GMT+09:00 Josh Poimboeuf <jpoimboe@xxxxxxxxxx>: > On Tue, Jul 10, 2018 at 10:35:16AM +0900, Masahiro Yamada wrote: >> Currently, users are allowed to enable STACK_VALIDATION regardless >> of the compiler capability. The top-level Makefile warns or breaks >> the build if it turns out that the host compiler cannot link libelf. >> >> Move the libelf test to Kconfig so that users can enable the feature >> only when the host compiler can build the objtool. The ugly check >> in the Makefile will go away. >> >> Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> >> Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> > > Actually, looking at this again, I want to rescind my ack. > > This patches changes the behavior in a subtle (but important) way. > > Before, if I did "make defconfig", it would *always* choose the ORC > unwinder. Then, if I didn't have libelf-devel, the build would fail and > it would tell me what I need to install. > > But now with this patch, if I do "make defconfig", the generated config > actually changes based on what I happen to have installed on my build > system. If I don't have libelf-devel, then it silently chooses the > non-default unwinder (frame pointer). > > This is a subtle difference, but IMO it's dangerous, because it will > silently enable the frame pointer unwinder for the majority of new > systems, even though it's not the default. > > I strongly prefer the original behavior, because we really want to > encourage people to use the ORC unwinder, even if that means they have > to install a package to build it. > > Also -- in general -- I suspect that silently changing the defaults like > this will create a lot of bad surprises. The output of "make defconfig" > should be predictable and not dependent on what RPMs I happen to have > installed. Actually, we had similar discussion for stack protector. First, Kees liked to let the build fail instead of disabling the stack protector silently: https://lkml.org/lkml/2018/2/9/697 Linus said: But yes, I also reacted to your earlier " It can't silently rewrite it to _REGULAR because the compiler support for _STRONG regressed." Because it damn well can. If the compiler doesn't support -fstack-protector-strong, we can just fall back on -fstack-protector. Silently. No extra crazy complex logic for that either. (https://lkml.org/lkml/2018/2/10/281) I hope this is the same pattern. -- Best Regards Masahiro Yamada -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
