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

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Message-ID: <CABCJKudwf11wAbv9NdKh_FN-Z+pLaupMHJxNGtRKK1-1D94hCQ@mail.gmail.com>
Date: Wed, 12 Feb 2025 08:52:27 -0800
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Peter Zijlstra <peterz@...radead.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 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)))
...

Sami