linux-kernel - Re: [PATCH] ftrace: x86: Fix a compile error about get_kernel

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Message-ID: <20250213100836.GC28068@noisy.programming.kicks-ass.net>
Date: Thu, 13 Feb 2025 11:08:36 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Steven Rostedt <rostedt@...dmis.org>,
	"Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
	Gabriel de Perthuis <g2p.code@...il.com>,
	Haiyue Wang <haiyuewa@....com>, Mark Rutland <mark.rutland@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-trace-kernel@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ftrace: x86: Fix a compile error about
 get_kernel_nofault()

On Wed, Feb 12, 2025 at 08:52:27AM -0800, Sami Tolvanen wrote:
> On Tue, Feb 11, 2025 at 7:49 AM Steven Rostedt <rostedt@...dmis.org> wrote:
> >
> > On Tue, 11 Feb 2025 11:09:14 +0100
> > Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > > I was aiming my patch for x86/core, but if there's a reason to expedite
> > > them, I can stick it in x86/urgent I suppose.
> > >
> > > Just need a reason -- what's this compile error nonsense about, my
> > > kernels build just fine?
> >
> > Masami,
> >
> > Do you have a config that fails to build without this fix? If so, can you
> > please reply with it, and then this can go in as a quick fix.
> 
> x86 builds with both CONFIG_GENDWARFKSYMS and CONFIG_FUNCTION_TRACER
> are broken without this fix. Here's how to reproduce:
> 
> $ make defconfig
> $ ./scripts/config -e DEBUG_INFO -e DEBUG_INFO_DWARF5 -e MODVERSIONS
> -e GENDWARFKSYMS -e FUNCTION_TRACER
> $ make olddefconfig && make -j
> ...
> In file included from ./arch/x86/include/asm/asm-prototypes.h:2,
>                  from <stdin>:3:
> ./arch/x86/include/asm/ftrace.h: In function ‘arch_ftrace_get_symaddr’:
> ./arch/x86/include/asm/ftrace.h:46:21: error: implicit declaration of
> function ‘get_kernel_nofault’ [-Wimplicit-function-declaration]
>    46 |                 if (get_kernel_nofault(instr, (u32
> *)(fentry_ip - ENDBR_INSN_SIZE)))
> ...

It breaks much sooner, complaining about not having dwarf.h.. let me go
figure out what package provides that :/

Anyway, thanks, I'll go see if my patch helps here.