Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH v3 04/23] linux/net.h: use unique identifier for each
 struct _ddebug
To:     Joe Perches <joe@perches.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jason Baron <jbaron@akamai.com>
Cc:     linux-kernel@vger.kernel.org, netdev@vger.kernel.org
References: <20181009112013.14238-1-linux@rasmusvillemoes.dk>
 <20181109231021.11658-1-linux@rasmusvillemoes.dk>
 <20181109231021.11658-5-linux@rasmusvillemoes.dk>
 <2358250f27022be9eb5c4e6a3d95ee869c3af45f.camel@perches.com>
From:   Rasmus Villemoes <linux@rasmusvillemoes.dk>
Message-ID: <e35f20ed-d93b-89ca-4123-a088c65df902@rasmusvillemoes.dk>
Date:   Sat, 10 Nov 2018 00:31:47 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.2.1
MIME-Version: 1.0
In-Reply-To: <2358250f27022be9eb5c4e6a3d95ee869c3af45f.camel@perches.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 10/11/2018 00.22, Joe Perches wrote:
> On Sat, 2018-11-10 at 00:10 +0100, Rasmus Villemoes wrote:
>> Changes on x86-64 later in this series require that all struct _ddebug
>> descriptors in a translation unit uses distinct identifiers. Realize
>> that for net_dbg_ratelimited by generating such an identifier via
>> __UNIQUE_ID and pass that to an extra level of macros.
>>
>> No functional change.
> 
> Why does this require an extra indirection _<macro>?
> 

Because the identifier used in the

>>  	DEFINE_DYNAMIC_DEBUG_METADATA(descriptor, fmt);

line must be the same as the one in the

>>  	if (DYNAMIC_DEBUG_BRANCH(descriptor) &&	

line. That identifier used to be simply "descriptor", with C scope rules
making that ok. But because of the asm games I'm playing later, I need
to generate a fresh identifier for each instance. That identifier must
be referenced in two places in the C source - hence the need to use an
extra level of macros to have the __UNIQUE_ID() expanded before
_net_dbg_ratelimited gets expanded.

More or less every use of __UNIQUE_ID requires such an extra level
(because one very rarely needs to use an identifier exactly once - the
point of giving stuff a name is to refer to it again.)

Rasmus