linux-kernel - Re: [PATCH] cris: arch-v10: kernel: kgdb: let is_dyn

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Date:	Fri, 10 Jul 2015 06:45:26 +0800
From:	Chen Gang <xili_gchen_5257@...mail.com>
To:	"Valdis.Kletnieks@...edu" <valdis.kletnieks@...edu>
CC:	"starvik@...s.com" <starvik@...s.com>,
	"jesper.nilsson@...s.com" <jesper.nilsson@...s.com>,
	"linux-cris-kernel@...s.com" <linux-cris-kernel@...s.com>,
	kernel mailing list <linux-kernel@...r.kernel.org>,
	Hans-Peter Nilsson <hans-peter.nilsson@...s.com>
Subject: Re: [PATCH] cris: arch-v10: kernel: kgdb: let is_dyn_brkp as extern
 variable

On 7/9/15 09:26, gchen gchen wrote:
> On 07/07/2015 06:28 AM, Chen Gang wrote:
>> On 7/6/15 18:31, Valdis.Kletnieks@...edu wrote:
>>> On Mon, 06 Jul 2015 15:49:20 +0800, Chen Gang said:
>>>> On 07/06/2015 02:25 AM, Valdis.Kletnieks@...edu wrote:
>>>>> On Sun, 05 Jul 2015 06:07:54 +0800, Chen Gang said:
>>>>>> For upstream cris toolchain (gcc is 6.0
>>>>>
>>>>> typo?
>>>>>
>>>>
>>>> Do you mean "toolchain" -> "tool chain"?
>>>
>>> No, I was wondering where a gcc 6.0 managed to escape when 5.1 just got
>>> released about 2 weeks ago....
>>>
>>

gcc 5.1 with the same fedora configuration also causes the same issue:

  [root@...alhost gcc]# /upstream/release-cris-fedora-conf/bin/cris-linux-gnu-gcc -v
  Using built-in specs.
  COLLECT_GCC=/upstream/release-cris-fedora-conf/bin/cris-linux-gnu-gcc
  COLLECT_LTO_WRAPPER=/upstream/release-cris-fedora-conf/libexec/gcc/cris-linux-gnu/5.1.0/lto-wrapper
  Target: cris-linux-gnu
  Configured with: ../gcc/configure --disable-nls --prefix=/upstream/release-cris-fedora-conf --disable-decimal-float --disable-dependency-tracking --disable-gold --disable-libgomp --disable-libmudflap --disable-libquadmath --disable-libssp --disable-nls --disable-plugin --disable-shared --disable-silent-rules --disable-sjlj-exceptions --disable-threads --enable-gnu-unique-object --enable-initfini-array --enable-languages=c --enable-linker-build-id --enable-nls --enable-obsolete --enable-targets=all --target=cris-linux-gnu --with-linker-hash-style=gnu --with-system-libunwind --with-system-zlib --without-headers
  Thread model: single
  gcc version 5.1.0 (GCC) 

So we need add 'volatile' for the static global variable which is used
between C code and assembly code. I shall send patch v2 for it within
this week (2015-07-12).

Welcome any members ideas, suggestions, and completions.

Thanks.

> 
> Oh, sorry, gcc 5.1 is the same, and at present, for me:
> 
>  - The new gcc have additional optimization for the static variables. It
>    should notice about the related c code when optimizing, but gcc has
>    no idea about assembly code (it should passes them to gas, directly).
> 
>  - If one want gcc skip the related optimization, it can use 'volatile'
>    for it (the static variable which may be used by both c code and
>    assembly code in one file).
> 
>  - So I guess, we need add 'volatile' to the related static variable, we
>    do not want to disable this optimization only because of this issue.
> 
> Welcome any additional ideas, suggestions and completions.
> 
>> OK, thanks. At present, gcc 6.0 is the latest in master branch.
>>
>> After check fedora released toolchain (gcc 4.9.1, binutils 2.25), it has
>> no issue (support static variable in our case). So this patch can be
>> dropped, and I shall try:
>>
>>  - Use the same configuration parameters of fedora released toolchain to
>>    build the upstream latest cross toolchain again, and try.
>>
>>  - If it still has issue (not support static variable), I shall try to
>>    fix it.
>>
>>
>> Thanks.
>>
> 
> --
> Chen Gang
> 
> Open, share, and attitude like air, water, and life which God blessed
>  		 	   		  
> 

-- 
Chen Gang

Open, share, and attitude like air, water, and life which God blessed
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