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SubjectRe: [PATCH 00/10] ftrace: Add register_ftrace_direct()
On Fri, 8 Nov 2019 16:51:00 -0600
Josh Poimboeuf <jpoimboe@redhat.com> wrote:

> Here's the fix for the objtool warning:

Thanks, I applied it (will push it soon).

-- Steve

>
> From: Josh Poimboeuf <jpoimboe@redhat.com>
> Subject: [PATCH] ftrace/x86: Tell objtool to ignore nondeterministic ftrace stack layout
>
> Objtool complains about the new ftrace direct trampoline code:
>
> arch/x86/kernel/ftrace_64.o: warning: objtool: ftrace_regs_caller()+0x190: stack state mismatch: cfa1=7+16 cfa2=7+24
>
> Typically, code has a deterministic stack layout, such that at a given
> instruction address, the stack frame size is always the same.
>
> That's not the case for the new ftrace_regs_caller() code after it
> adjusts the stack for the direct case. Just plead ignorance and assume
> it's always the non-direct path. Note this creates a tiny window for
> ORC to get confused.
>
> Reported-by: Steven Rostedt <rostedt@goodmis.org>
> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> ---
> arch/x86/include/asm/unwind_hints.h | 8 ++++++++
> arch/x86/kernel/ftrace_64.S | 12 +++++++++++-
> 2 files changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/unwind_hints.h b/arch/x86/include/asm/unwind_hints.h
> index 0bcdb1279361..f5e2eb12cb71 100644
> --- a/arch/x86/include/asm/unwind_hints.h
> +++ b/arch/x86/include/asm/unwind_hints.h
> @@ -86,6 +86,14 @@
> UNWIND_HINT sp_offset=\sp_offset
> .endm
>
> +.macro UNWIND_HINT_SAVE
> + UNWIND_HINT type=UNWIND_HINT_TYPE_SAVE
> +.endm
> +
> +.macro UNWIND_HINT_RESTORE
> + UNWIND_HINT type=UNWIND_HINT_TYPE_RESTORE
> +.endm
> +
> #else /* !__ASSEMBLY__ */
>
> #define UNWIND_HINT(sp_reg, sp_offset, type, end) \
> diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
> index 5d946ab40b52..1c79624a36b2 100644
> --- a/arch/x86/kernel/ftrace_64.S
> +++ b/arch/x86/kernel/ftrace_64.S
> @@ -175,6 +175,8 @@ ENTRY(ftrace_regs_caller)
> /* Save the current flags before any operations that can change them */
> pushfq
>
> + UNWIND_HINT_SAVE
> +
> /* added 8 bytes to save flags */
> save_mcount_regs 8
> /* save_mcount_regs fills in first two parameters */
> @@ -249,8 +251,16 @@ GLOBAL(ftrace_regs_call)
> 1: restore_mcount_regs
>
>
> +2:
> + /*
> + * The stack layout is nondetermistic here, depending on which path was
> + * taken. This confuses objtool and ORC, rightfully so. For now,
> + * pretend the stack always looks like the non-direct case.
> + */
> + UNWIND_HINT_RESTORE
> +
> /* Restore flags */
> -2: popfq
> + popfq
>
> /*
> * As this jmp to ftrace_epilogue can be a short jump

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