On Mon, 16 May, at 01:05:45PM, Linus Torvalds wrote: > > So that whole 8-vs-16 offset confusion depends on the frame pointer! > If frame pointers were enabled, it will be 16. If they weren't, it > will be 8. That patch that changes it from 8 to 16 will just move the > bug around. Before, it was correct when frame pointers were disabled > and buggy otherwise. Now, it's correct if frame pointers are enabled, > and buggy otherwise. Urgh, right.
We didn't always use frame pointers in efi_call(), they were introduced in commit 779c433b8ea5c ("x86/asm/efi: Create a stack frame in efi_call()") earlier this year to stop objtool complaining. I admit I totally missed the part about pulling arguments off the stack when I reviewed that patch. > I may be missing something, but I think that commit is pure garbage. You're correct. > I think the right fix is to just get rid of that silly conditional > frame pointer thing, and always use frame pointers in this stub > function. And then we don't need that (odd) load to get the old stack > pointer into %rax - we can just use the frame pointer. > > Something like the attached completely untested patch. Looks good to me, but I haven't tested it. Now I'm wondering whether other users of FRAME_BEGIN/FRAME_END make this same mistake. Coccinelle might be able to detect it perhaps.