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Date: Fri, 8 Nov 2019 20:00:37 -0500 From: Steven Rostedt <rostedt@...dmis.org> To: Josh Poimboeuf <jpoimboe@...hat.com> Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, X86 ML <x86@...nel.org>, Nadav Amit <nadav.amit@...il.com>, Andy Lutomirski <luto@...nel.org>, Dave Hansen <dave.hansen@...ux.intel.com>, Song Liu <songliubraving@...com>, Masami Hiramatsu <mhiramat@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Daniel Bristot de Oliveira <bristot@...hat.com>, Alexei Starovoitov <alexei.starovoitov@...il.com> Subject: Re: [PATCH 00/10] ftrace: Add register_ftrace_direct() On Fri, 8 Nov 2019 16:51:00 -0600 Josh Poimboeuf <jpoimboe@...hat.com> wrote: > Here's the fix for the objtool warning: Thanks, I applied it (will push it soon). -- Steve > > From: Josh Poimboeuf <jpoimboe@...hat.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@...dmis.org> > Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.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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