linux-kernel - Re: [PATCH] export.h: reduce __ksymtab_strings string duplication by using "MS" section flags

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Message-ID: <b280c412-432b-ff54-acbd-a6bcc74b6e72@rasmusvillemoes.dk>
Date:   Mon, 25 Nov 2019 10:29:30 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Jessica Yu <jeyu@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Matthias Maennich <maennich@...gle.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        "binutils@...rceware.org" <binutils@...rceware.org>
Subject: Re: [PATCH] export.h: reduce __ksymtab_strings string duplication by
 using "MS" section flags

cc += binutils ML

[on @progbits v %progbits in generic (data only) assembly code]

On 22/11/2019 12.44, Masahiro Yamada wrote:
> On Fri, Nov 22, 2019 at 1:09 AM Jessica Yu <jeyu@...nel.org> wrote:
>>

>> I think this would work, and it feels like the more correct solution
>> especially if arm isn't the only one with the odd progbits char. It
>> might be overkill if it's just arm that's affected though. I leave it
>> to Masahiro to see what he prefers.
>>
> 
> 
> BTW, is there any reason why
> not use %progbits all the time?
> 
> 
> include/linux/init.h hard-codes %progbits
> 
>    #define __INITDATA .section ".init.data","aw",%progbits
>    #define __INITRODATA .section ".init.rodata","a",%progbits
> 
> 
> So, my understanding is '%' works for all architectures,
> but it is better to ask 0-day bot to test it.

It seems that you're absolutely right. The binutils source has code like

+             if (*input_line_pointer == '@' || *input_line_pointer == '%')
+               {
+                 ++input_line_pointer;
+                 if (strncmp (input_line_pointer, "progbits",
+                              sizeof "progbits" - 1) == 0)
+                   {
+                     type = SHT_PROGBITS;
+                     input_line_pointer += sizeof "progbits" - 1;
+                   }
+                 else if (strncmp (input_line_pointer, "nobits",
+                                   sizeof "nobits" - 1) == 0)
+                   {
+                     type = SHT_NOBITS;
+                     input_line_pointer += sizeof "nobits" - 1;
+                   }


all the way back from

commit 252b5132c753830d5fd56823373aed85f2a0db63 (tag: binu_ss_19990502)
Author: Richard Henderson <rth@...hat.com>
Date:   Mon May 3 07:29:11 1999 +0000

    19990502 sourceware import

So yes, let's just try unconditionally using %progbits, that makes
everything much simpler.

The only reason I thought one needed to do it differently on ARM is this
from the gas docs:

===
   The optional TYPE argument may contain one of the following
constants:

'@...gbits'
     section contains data
...
   Note on targets where the '@' character is the start of a comment (eg
ARM) then another character is used instead.  For example the ARM port
uses the '%' character.
===

That doesn't suggest the possibility that % or some other character
might work on all architectures.

Jessica, can you resend using just %progbits to let kbuild chew on that?
Please include a comment about the misleading gas documentation.

Rasmus