linux-kernel - Re: [PATCH] samples: ftrace: replace bti assembly with hint for older compiler

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Date:   Mon, 21 Aug 2023 17:41:21 +0200
From:   Florent Revest <revest@...omium.org>
To:     "GONG, Ruiqi" <gongruiqi@...weicloud.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        gongruiqi1@...wei.com
Subject: Re: [PATCH] samples: ftrace: replace bti assembly with hint for older compiler

On Sun, Aug 20, 2023 at 1:10 PM GONG, Ruiqi <gongruiqi@...weicloud.com> wrote:
>
> When cross-building the arm64 kernel with allmodconfig using GCC 9.4,
> the following error occurs on multiple files under samples/ftrace/:
>
> /tmp/ccPC1ODs.s: Assembler messages:
> /tmp/ccPC1ODs.s:8: Error: selected processor does not support `bti c'
>
> Fix this issue by replacing `bti c` with `hint 34`, which is compatible
> for the older compiler.

I see this hint is already used in
tools/testing/selftests/arm64/fp/rdvl.S but I'm curious why it isn't
used in other parts of the kernel like
arch/arm64/kernel/entry-ftrace.S or
tools/testing/selftests/arm64/bti/syscall.S