linux-kernel - Re: [PATCH v2 04/10] powerpc/traps: Use REG_FMT in show_signal

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Message-ID: <26f07092cdde378ebb42c1034badde1b56521c36.camel@perches.com>
Date:   Fri, 27 Jul 2018 10:18:08 -0700
From:   Joe Perches <joe@...ches.com>
To:     LEROY Christophe <christophe.leroy@....fr>,
        Murilo Opsfelder Araujo <muriloo@...ux.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, "Tobin C . Harding" <me@...in.cc>,
        Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
        Simon Guo <wei.guo.simon@...il.com>,
        Paul Mackerras <paulus@...ba.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Michael Neuling <mikey@...ling.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Cyril Bur <cyrilbur@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Balbir Singh <bsingharora@...il.com>,
        Andrew Donnellan <andrew.donnellan@....ibm.com>,
        Alastair D'Silva <alastair@...ilva.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 04/10] powerpc/traps: Use REG_FMT in show_signal_msg()

On Fri, 2018-07-27 at 18:40 +0200, LEROY Christophe wrote:
> Murilo Opsfelder Araujo <muriloo@...ux.ibm.com> a écrit :
> 
> > Simplify the message format by using REG_FMT as the register format.  This
> > avoids having two different formats and avoids checking for MSR_64BIT.
> 
> Are you sure it is what we want ?
> 
> Won't it change the behaviour for a 32 bits app running on a 64bits kernel ?

[]

> > diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
[]
> > @@ -311,17 +311,13 @@ static bool show_unhandled_signals_ratelimited(void)
> >  static void show_signal_msg(int signr, struct pt_regs *regs, int code,
> >  			    unsigned long addr)
> >  {
> > -	const char fmt32[] = KERN_INFO "%s[%d]: unhandled signal %d " \
> > -		"at %08lx nip %08lx lr %08lx code %x\n";
> > -	const char fmt64[] = KERN_INFO "%s[%d]: unhandled signal %d " \
> > -		"at %016lx nip %016lx lr %016lx code %x\n";
> > -
> >  	if (!unhandled_signal(current, signr))
> >  		return;
> > 
> > -	printk(regs->msr & MSR_64BIT ? fmt64 : fmt32,
> > -	       current->comm, current->pid, signr,
> > -	       addr, regs->nip, regs->link, code);
> > +	pr_info("%s[%d]: unhandled signal %d at "REG_FMT \

I think it better to use a space after the close "
and also the line continuation is unnecessary.

> > +		" nip "REG_FMT" lr "REG_FMT" code %x\n",

And spaces before the open quotes too.

I'd also prefer the format on a single line:

	pr_info("%s[%d]: unhandled signal %d at " REG_FMT " nip " REG_FMT " lr " REG_FMT " code %x\n",

> > +		current->comm, current->pid, signr, addr,
> > +		regs->nip, regs->link, code);

Seeing as these are all unsigned long, a better way to do
this is to use %p and cast to pointer.

This might be better anyway as this output exposes pointer
addresses and instead would now use pointer hashed output.

	pr_info("%s[%d]: unhandled signal %d at %p nip %p lr %p code %x\n",
		current->comm, current->pid, signr,
		(void *)addr, (void *)regs->nip, (void *)regs->link, code);

Use %px if you _really_ need to emit unhashed addresses.

see: Documentation/core-api/printk-formats.rst