linux-kernel - Re: [PATCH v8 04/28] x86/asm/entry: annotate THUNKs

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Date:   Thu, 15 Aug 2019 14:43:28 +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
Subject: Re: [PATCH v8 04/28] x86/asm/entry: annotate THUNKs

On Thu, Aug 08, 2019 at 12:38:30PM +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.
> 
> The common tail .L_restore is put inside SYM_CODE_START_LOCAL_NOALIGN
> and SYM_CODE_END too.

What is that needed for? It is a local label...

> The result:
>  Value  Size Type    Bind   Vis      Ndx Name
>   0000    28 FUNC    GLOBAL DEFAULT    1 trace_hardirqs_on_thunk
>   001c    28 FUNC    GLOBAL DEFAULT    1 trace_hardirqs_off_thunk
>   0038    24 FUNC    GLOBAL DEFAULT    1 lockdep_sys_exit_thunk
>   0050    24 FUNC    GLOBAL DEFAULT    1 ___preempt_schedule
>   0068    24 FUNC    GLOBAL DEFAULT    1 ___preempt_schedule_notra

No difference except alignment:

before:
 70545: ffffffff81001c20    28 FUNC    GLOBAL DEFAULT    1 trace_hardirqs_off_thunk
 78965: ffffffff81001c00    28 FUNC    GLOBAL DEFAULT    1 trace_hardirqs_on_thunk
 82545: ffffffff81001c80    24 FUNC    GLOBAL DEFAULT    1 ___preempt_schedule_notra
 86963: ffffffff81001c40    24 FUNC    GLOBAL DEFAULT    1 lockdep_sys_exit_thunk
 88045: ffffffff81001c60    24 FUNC    GLOBAL DEFAULT    1 ___preempt_schedule

after:
 70545: ffffffff81001c10    28 FUNC    GLOBAL DEFAULT    1 trace_hardirqs_off_thunk
 78965: ffffffff81001bf4    28 FUNC    GLOBAL DEFAULT    1 trace_hardirqs_on_thunk
 82545: ffffffff81001c5c    24 FUNC    GLOBAL DEFAULT    1 ___preempt_schedule_notra
 86963: ffffffff81001c2c    24 FUNC    GLOBAL DEFAULT    1 lockdep_sys_exit_thunk
 88045: ffffffff81001c44    24 FUNC    GLOBAL DEFAULT    1 ___preempt_schedule

-- 
Regards/Gruss,
    Boris.

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