On Tue, Jan 15, 2019 at 11:06:17AM -0800, Sean Christopherson wrote: > > I can see there are five options to solve it. > > > > 1) always inline vmx_vcpu_run() > > 2) always noinline vmx_vcpu_run() > > 3) add -fdiable-ipa-fnsplit option to Makefile for vmx.o > > 4) let STACK_FRAME_NON_STANDARD support part.* syntax. > > 5) trim-down vmx_vcpu_run() even more to not causing splitting by GCC. > > > > Option 1) and 2) seems give away the decision for user with > > CONFIG_CC_OPTIMIZE_FOR_(PERFORMANCE/SIZE). > > > > Option 3) prevents other functions there for splitting for optimization. > > > > Option 4) and 5) seems tricky to implement. > > > > I am not more leaning to 3) as only other fuction will miss splitting is > > vmx_segment_access_rights(). > > Option 4) is the most correct, but "tricky" is an understatement. Unless > Josh is willing to pick up the task it'll likely have to wait. > > There's actually a few more options: > > 6) Replace "pop %rbp" in the vmx_vmenter() asm blob with an open-coded > equivalent, e.g. "mov [%rsp], %rbp; add $8, %rsp". This runs an end- > around on objtool since objtool explicitly keys off "pop %rbp" and NOT > "mov ..., %rbp" (which is probably an objtool checking flaw?"). > > 7) Move the vmx_vmenter() asm blob and a few other lines of code into a > separate helper, e.g. __vmx_vcpu_run(), and mark that as having a > non-standard stack frame.
Do you mean moving the asm blob to a .S file instead of inline asm? If so, I think that's definitely a good idea. It would be a nice cleanup, regardless of the objtool false positive. That would allow vmx_vcpu_run() to be a "normal" C function which objtool can validate (and also create ORC data for). It would also prevent future nasty GCC optimizations (which was why the __noclone was needed in the first place). And also, I *think* objtool would no longer warn in that case, because there would no longer be any calls in the function after popping %rbp. Though if I'm wrong about that, I'd be glad to help fix the warning one way or another. -- Josh
