GNU bug report logs - #30820
Chunked store references in compiled code break grafting (again)

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Message #33 received at 30820 <at> debbugs.gnu.org (full text, mbox):

From: ludo <at> gnu.org (Ludovic Courtès)
To: Danny Milosavljevic <dannym <at> scratchpost.org>
Cc: 30820 <at> debbugs.gnu.org
Subject: Re: bug#30820: Chunked store references in compiled code break
 grafting (again)
Date: Mon, 19 Mar 2018 23:29:10 +0100

Heya,

Danny Milosavljevic <dannym <at> scratchpost.org> skribis:

>> The second issue is that the patch only ever worked with literal
>> strings.  It does not “see” strings in constant arrays like the ‘str’
>> array in the example above.
>> 
>> The gconv-module file name mentioned in the first message in this bug
>> report is an example of a string assigned to a static array, in
>> iconv/gconv_conf.c:
>> 
>>   /* This is the default path where we look for module lists.  */
>>   static const char default_gconv_path[] = GCONV_PATH;
>
> I don't understand why this is a problem.  Grafting would just
> mutate default_gconv_path, right?  Who cares how the runtime memcpy
> works (if there's no literal as source)?

At compile-time, GCC finds out that ‘default_gconv_path’ is used only
in one place, in an strcpy call.  Thus, it chooses to use the movabs
optimization, and as a consequence, to split ‘default_gconv_path’ in
8-byte chunks.  It can do so because it’s ‘static’.

Ludo’.

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