Re: [tip:x86/alternatives 14/14] arch/x86/kvm/kvm.o: warning: objtool: .altinstr_replacement+0xc5: call without frame pointer save/setup

Sean Christopherson
2024-06-18T14:24:51Z

On Tue, Jun 18, 2024, Peter Zijlstra wrote:
> On Fri, Jun 14, 2024 at 05:22:28PM +0200, Borislav Petkov wrote:
> > On Fri, Jun 14, 2024 at 04:15:14PM +0800, kernel test robot wrote:
> You sure? Afaict the thing is:
>
> $ OBJTOOL_ARGS="--verbose" make O=tmp-build/ arch/x86/kvm/
> ...
> arch/x86/kvm/kvm.o: warning: objtool: .altinstr_replacement+0xc5: call without frame pointer save/setup
> arch/x86/kvm/kvm.o: warning: objtool: em_loop.part.0+0x29: (alt)
> arch/x86/kvm/kvm.o: warning: objtool: em_loop.part.0+0x0: <=== (sym)
> 0000 0000000000028220 <em_loop.part.0>:
> 0000 28220: 0f b6 47 61 movzbl 0x61(%rdi),%eax
> 0004 28224: 3c e2 cmp $0xe2,%al
> 0006 28226: 74 2c je 28254 <em_loop.part.0+0x34>
> 0008 28228: 48 8b 57 10 mov 0x10(%rdi),%rdx
> 000c 2822c: 83 f0 05 xor $0x5,%eax
> 000f 2822f: 48 c1 e0 04 shl $0x4,%rax
> 0013 28233: 25 f0 00 00 00 and $0xf0,%eax
> 0018 28238: 81 e2 d5 08 00 00 and $0x8d5,%edx
> 001e 2823e: 80 ce 02 or $0x2,%dh
> 0021 28241: 48 05 00 00 00 00 add $0x0,%rax 28243: R_X86_64_32S em_setcc
> 0027 28247: 52 push %rdx
> 0028 28248: 9d popf
> 0029 28249: ff d0 call *%rax
> 002b 2824b: 90 nop
> 002c 2824c: 90 nop
> 002d 2824d: 90 nop
> 002e 2824e: 31 d2 xor %edx,%edx
> 0030 28250: 84 c0 test %al,%al
> 0032 28252: 74 1d je 28271 <em_loop.part.0+0x51>
> 0034 28254: 55 push %rbp
> 0035 28255: 48 63 b7 d0 00 00 00 movslq 0xd0(%rdi),%rsi
> 003c 2825c: 48 03 b7 90 00 00 00 add 0x90(%rdi),%rsi
> 0043 28263: 48 89 e5 mov %rsp,%rbp
> 0046 28266: e8 05 fe ff ff call 28070 <assign_eip>
> 004b 2826b: 5d pop %rbp
> 004c 2826c: e9 00 00 00 00 jmp 28271 <em_loop.part.0+0x51> 2826d: R_X86_64_PLT32 __x86_return_thunk-0x4
> 0051 28271: 89 d0 mov %edx,%eax
> 0053 28273: e9 00 00 00 00 jmp 28278 <em_loop.part.0+0x58> 28274: R_X86_64_PLT32 __x86_return_thunk-0x4
> 0058 28278: 0f 1f 84 00 00 00 00 00 nopl 0x0(%rax,%rax,1)
>
> Which is in fact test_cc() from em_loop().
>
> Now, that .config is a FRAME_POINTER build, and the fast-call thing
> don't do frames, so it is right to complain. Big question is why it
> didn't complain previously I suppose.
>
> Also, notably, this patch:
>
> https://lkml.kernel.org/r/20231204093732.323101886@infradead.org
>
> cures things.

Speaking of that series, do you need/want any help pushing it along? I ran into
build issues[*] and didn't have the cycles to fully figure things out at the time.

This fails for some of my builds that end up with CONFIG_OBJTOOl=n. Adding a
stub for ASM_ANNOTATE() gets me past that:

@@ -156,6 +171,7 @@
#define STACK_FRAME_NON_STANDARD(func)
#define STACK_FRAME_NON_STANDARD_FP(func)
#define ANNOTATE_NOENDBR
+#define ASM_ANNOTATE(x)
#define ASM_REACHABLE
#else
#define ANNOTATE_INTRA_FUNCTION_CALL

but then I run into other issues:

arch/x86/kernel/relocate_kernel_32.S: Assembler messages:
arch/x86/kernel/relocate_kernel_32.S:96: Error: Parameter named `type' does not exist for macro `annotate'
arch/x86/kernel/relocate_kernel_32.S:166: Error: Parameter named `type' does not exist for macro `annotate'
arch/x86/kernel/relocate_kernel_32.S:174: Error: Parameter named `type' does not exist for macro `annotate'
arch/x86/kernel/relocate_kernel_32.S:200: Error: Parameter named `type' does not exist for macro `annotate'
arch/x86/kernel/relocate_kernel_32.S:220: Error: Parameter named `type' does not exist for macro `annotate'
arch/x86/kernel/relocate_kernel_32.S:285: Error: Parameter named `type' does not exist for macro `annotate'

[*] https://lore.kernel.org/all/ZXEEbrI7K6XGr2dN@google.com