linux-kernel - Re: [for-next][PATCH 4/6] scripts/sorttable: Zero out weak functions in mcount

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Message-ID: <20250224180805.GA1536711@ax162>
Date: Mon, 24 Feb 2025 10:08:05 -0800
From: Nathan Chancellor <nathan@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, Masami Hiramatsu <mhiramat@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	bpf <bpf@...r.kernel.org>, Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Masahiro Yamada <masahiroy@...nel.org>,
	Nicolas Schier <nicolas@...sle.eu>,
	Zheng Yejian <zhengyejian1@...wei.com>,
	Martin Kelly <martin.kelly@...wdstrike.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Vasily Gorbik <gor@...ux.ibm.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>
Subject: Re: [for-next][PATCH 4/6] scripts/sorttable: Zero out weak functions
 in mcount_loc table

Hi Steve,

On Wed, Feb 19, 2025 at 10:18:19AM -0500, Steven Rostedt wrote:
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 728ecda6e8d4..e3f89924f603 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -7004,6 +7004,7 @@ static int ftrace_process_locs(struct module *mod,
>  	unsigned long count;
>  	unsigned long *p;
>  	unsigned long addr;
> +	unsigned long kaslr;
>  	unsigned long flags = 0; /* Shut up gcc */
>  	int ret = -ENOMEM;
>  
> @@ -7052,6 +7053,9 @@ static int ftrace_process_locs(struct module *mod,
>  		ftrace_pages->next = start_pg;
>  	}
>  
> +	/* For zeroed locations that were shifted for core kernel */
> +	kaslr = !mod ? kaslr_offset() : 0;
> +
>  	p = start;
>  	pg = start_pg;
>  	while (p < end) {
> @@ -7063,7 +7067,7 @@ static int ftrace_process_locs(struct module *mod,
>  		 * object files to satisfy alignments.
>  		 * Skip any NULL pointers.
>  		 */
> -		if (!addr) {
> +		if (!addr || addr == kaslr) {
>  			skipped++;
>  			continue;
>  		}

Our CI and KernelCI reports that this change as commit ef378c3b8233
("scripts/sorttable: Zero out weak functions in mcount_loc table") in
next-20250224 breaks when an architecture does not have kaslr_offset()
defined:

  $ make -skj"$(nproc)" ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- mrproper allmodconfig kernel/trace/ftrace.o
  kernel/trace/ftrace.c: In function 'ftrace_process_locs':
  kernel/trace/ftrace.c:7074:24: error: implicit declaration of function 'kaslr_offset' [-Wimplicit-function-declaration]
   7074 |         kaslr = !mod ? kaslr_offset() : 0;
        |                        ^~~~~~~~~~~~

https://lore.kernel.org/CACo-S-0GeJjWWcrGvos_Avg2FwGU2tj2QZpgoHOvPT+YbyknSg@mail.gmail.com/

Cheers,
Nathan