linux-kernel - Re: [patch V4 part 5 13/31] x86/irq: Convey vector as argument and not in ptregs

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Message-ID: <87v9l25yk7.fsf@nanos.tec.linutronix.de>
Date:   Mon, 11 May 2020 16:35:52 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Lai Jiangshan <jiangshanlai+lkml@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [patch V4 part 5 13/31] x86/irq: Convey vector as argument and not in ptregs

Lai,

Lai Jiangshan <jiangshanlai+lkml@...il.com> writes:
> On Tue, May 5, 2020 at 10:23 PM Thomas Gleixner <tglx@...utronix.de> wrote:
>> +SYM_CODE_START(irq_entries_start)
>> +    vector=FIRST_EXTERNAL_VECTOR
>> +    .rept (FIRST_SYSTEM_VECTOR - FIRST_EXTERNAL_VECTOR)
>> +       UNWIND_HINT_IRET_REGS
>> +       .byte   0x6a, vector
>> +       jmp     common_interrupt
>> +       .align  8
>> +    vector=vector+1
>> +    .endr
>> +SYM_CODE_END(irq_entries_start)
>
> Using ".byte   0x6a, vector" is somewhat ugly.
>
> I hope it should be " pushq $(s8_to_s64(vector))", which can also
> help to reduce bunches of comments about ".byte   0x6a, vector".
>
> However, I don't know how to implement s8_to_s64() here.

Neither do I.

> But at least the following code works (generates the same two-byte
> machine code as ".byte 0x6a, vector" does):
>
>         .if vector < 128
>         pushq $(vector)
>         .else
>         pushq $(0xffffffffffffff00+vector)
>         .endif

Only slightly less ugly and needs as much commentry as the above.

Thanks,

        tglx