linux-kernel - Re: [patch V6 19/37] x86/irq: Convey vector as argument and not in ptregs

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Message-ID: <20200522192615.5asnbnanfdiofaj6@treble>
Date:   Fri, 22 May 2020 14:26:15 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "Paul E. McKenney" <paulmck@...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>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Will Deacon <will@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Wei Liu <wei.liu@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Jason Chen CJ <jason.cj.chen@...el.com>,
        Zhao Yakui <yakui.zhao@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [patch V6 19/37] x86/irq: Convey vector as argument and not in
 ptregs

On Fri, May 22, 2020 at 02:48:53PM -0400, Boris Ostrovsky wrote:
> > Yes. They just make objtool very unhappy:
> >
> > arch/x86/entry/entry_64.o: warning: objtool: .entry.text+0xfd0: special:
> > can't find orig instruction
> >
> > Peter suggested to use:
> >
> >       .pos = .
> >       .byte..
> >       jmp
> >       .nops (pos + 8) - .
> 
> 
> Unfortunately this (.nops directive) only works for newer assemblers
> (2.31, per
> https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob_plain;f=gas/NEWS;h=9a3f352108e439754688e19e63a6235b38801182;hb=5eb617a71463fa6810cd14f57adfe7a1efc93a96)
> 
> 
> I have 2.27 and things don't go well.

A single nop should be fine, since gas will complain if it tries to move
the IP backwards.  (Also I'd vote for normal indentation instead of the
"assembler magic at 4 spaces" thing.)

.align 8
SYM_CODE_START(irq_entries_start)
	vector = FIRST_EXTERNAL_VECTOR
	.rept (FIRST_SYSTEM_VECTOR - FIRST_EXTERNAL_VECTOR)
		pos = .
		UNWIND_HINT_IRET_REGS
		.byte	0x6a, vector
		jmp	asm_common_interrupt
		nop
		.  = pos + 8
		vector = vector + 1
	.endr
SYM_CODE_END(irq_entries_start)

-- 
Josh