Re: [PATCH 03/11] objtool: Convert ANNOTATE_RETPOLINE_SAFE to ANNOTATE

James Houghton
2024-09-13T20:47:13Z

Hi Peter,

On Wed, 6 Dec 2023, Sean Christopherson wrote:
> On Mon, Dec 04, 2023, Peter Zijlstra wrote:
> >
> > --- a/arch/x86/include/asm/nospec-branch.h
> > +++ b/arch/x86/include/asm/nospec-branch.h
> > @@ -193,12 +193,7 @@
> > * objtool the subsequent indirect jump/call is vouched safe for retpoline
> > * builds.
> > */
> > -.macro ANNOTATE_RETPOLINE_SAFE
> > -.Lhere_\@:
> > - .pushsection .discard.retpoline_safe
> > - .long .Lhere_\@
> > - .popsection
> > -.endm
> > +#define ANNOTATE_RETPOLINE_SAFE ANNOTATE type=ANNOTYPE_RETPOLINE_SAFE
> >
> > /*
> > * (ab)use RETPOLINE_SAFE on RET to annotate away 'bare' RET instructions
> > @@ -317,11 +312,7 @@
> >
> > #else /* __ASSEMBLY__ */
> >
> > -#define ANNOTATE_RETPOLINE_SAFE \
> > - "999:\n\t" \
> > - ".pushsection .discard.retpoline_safe\n\t" \
> > - ".long 999b\n\t" \
> > - ".popsection\n\t"
> > +#define ANNOTATE_RETPOLINE_SAFE ASM_ANNOTATE(ANNOTYPE_RETPOLINE_SAFE)
>
> 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'

Sean pointed me at this series recently. It seems like these compile errors
(and some others) go away with the following diff:

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 0bebdcad7ba1..036ab199859a 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -489,7 +489,7 @@ static inline void call_depth_return_thunk(void) {}
" .align 16\n" \
"903: lea 4(%%esp), %%esp;\n" \
" pushl %[thunk_target];\n" \
- " ret;\n" \
+ " ret;\n", \
X86_FEATURE_RETPOLINE, \
"lfence;\n" \
ANNOTATE_RETPOLINE_SAFE \
diff --git a/include/linux/objtool.h b/include/linux/objtool.h
index f6f80bfefe3b..e811b2ff3a9c 100644
--- a/include/linux/objtool.h
+++ b/include/linux/objtool.h
@@ -159,6 +159,7 @@
#define STACK_FRAME_NON_STANDARD_FP(func)
#define ANNOTATE_NOENDBR
#define ASM_REACHABLE
+#define ASM_ANNOTATE(x)
#else
#define ANNOTATE_INTRA_FUNCTION_CALL
.macro UNWIND_HINT type:req sp_reg=0 sp_offset=0 signal=0
@@ -169,7 +170,7 @@
.endm
.macro REACHABLE
.endm
-.macro ANNOTATE
+.macro ANNOTATE type:req
.endm
#endif

This series applies on top of the latest kvm-x86/next with only a few trivial
conflicts, so I hope you are able to send a new version.

I could send one for you, but I have no idea how to properly test it.