linux-kernel - Re: [PATCH v9 04/28] x86/asm/entry: Annotate THUNKs

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Date:   Mon, 14 Oct 2019 15:38:43 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Jiri Slaby <jslaby@...e.cz>
Cc:     tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        x86@...nel.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v9 04/28] x86/asm/entry: Annotate THUNKs

On Fri, Oct 11, 2019 at 01:50:44PM +0200, Jiri Slaby wrote:
> Place SYM_*_START_NOALIGN and SYM_*_END around the THUNK macro body.
> Preserve @function by FUNC (64bit) and CODE (32bit). Given it was not
> marked as aligned, use NOALIGN.

Yeah, I guess the NOALIGN is causing some relaxing of alignment because
the symbols all "move up", from looking at the addresses:

before:
$ readelf -a vmlinux | grep -E "\W(trace_hardirqs_o(n|ff)_thunk|lockdep_sys_exit_thunk|___preempt_schedule)"
 70007: ffffffff81001c60    28 FUNC    GLOBAL DEFAULT    1 trace_hardirqs_off_thunk
 78467: ffffffff81001c40    28 FUNC    GLOBAL DEFAULT    1 trace_hardirqs_on_thunk
 82067: ffffffff81001cc0    24 FUNC    GLOBAL DEFAULT    1 ___preempt_schedule_notra
 86509: ffffffff81001c80    24 FUNC    GLOBAL DEFAULT    1 lockdep_sys_exit_thunk
 87594: ffffffff81001ca0    24 FUNC    GLOBAL DEFAULT    1 ___preempt_schedule

after:
$ readelf -a vmlinux | grep -E "\W(trace_hardirqs_o(n|ff)_thunk|lockdep_sys_exit_thunk|___preempt_schedule)"
 70007: ffffffff81001c50    28 FUNC    GLOBAL DEFAULT    1 trace_hardirqs_off_thunk
 78467: ffffffff81001c34    28 FUNC    GLOBAL DEFAULT    1 trace_hardirqs_on_thunk
 82067: ffffffff81001c9c    24 FUNC    GLOBAL DEFAULT    1 ___preempt_schedule_notra
 86509: ffffffff81001c6c    24 FUNC    GLOBAL DEFAULT    1 lockdep_sys_exit_thunk
 87594: ffffffff81001c84    24 FUNC    GLOBAL DEFAULT    1 ___preempt_schedule

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette