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From: Jan Beulich <jbeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: "Stefano Stabellini" <sstabellini@kernel.org>,
	"Julien Grall" <julien@xen.org>, "Wei Liu" <wl@xen.org>,
	"Konrad Rzeszutek Wilk" <konrad.wilk@oracle.com>,
	"George Dunlap" <George.Dunlap@eu.citrix.com>,
	"Ian Jackson" <ian.jackson@eu.citrix.com>,
	"Anthony PERARD" <anthony.perard@citrix.com>,
	xen-devel@lists.xenproject.org,
	"Volodymyr Babchuk" <Volodymyr_Babchuk@epam.com>,
	"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [Xen-devel] [XEN PATCH 8/8] xen: Move GCC_HAS_VISIBILITY_ATTRIBUTE to Kconfig and common
Date: Fri, 13 Dec 2019 12:27:09 +0100	[thread overview]
Message-ID: <e7e4c191-1f6c-616d-98b9-3f1fbd0dcb42@suse.com> (raw)
In-Reply-To: <dfebae5a-90a6-e898-5f49-701d6e2aa7fd@citrix.com>

On 12.12.2019 20:04, Andrew Cooper wrote:
> On 12/12/2019 18:27, Anthony PERARD wrote:
>> diff --git a/xen/include/xen/compiler.h b/xen/include/xen/compiler.h
>> index ff6c0f5cdd18..8c846261d241 100644
>> --- a/xen/include/xen/compiler.h
>> +++ b/xen/include/xen/compiler.h
>> @@ -78,7 +78,7 @@
>>  #define __must_be_array(a) \
>>    BUILD_BUG_ON_ZERO(__builtin_types_compatible_p(typeof(a), typeof(&a[0])))
>>  
>> -#ifdef GCC_HAS_VISIBILITY_ATTRIBUTE
>> +#ifdef CONFIG_CC_HAS_VISIBILITY_ATTRIBUTE
>>  /* Results in more efficient PIC code (no indirections through GOT or PLT). */
>>  #pragma GCC visibility push(hidden)
> 
> (I realise we are getting into archaeology, but) Why do we have this as
> a pragma gcc?
> 
> Surely it would be simpler to just feed -fvisibility=hidden into CFLAGS?

No, as per the (admittedly not very explicit) commit message of the
change introducing it. Quoting gcc documentation for making it more
obvious:

"extern declarations are not affected by ‘-fvisibility’, so a lot of code
 can be recompiled with ‘-fvisibility=hidden’ with no modifications.
 However, this means that calls to extern functions with no explicit
 visibility use the PLT, so it is more effective to use
 __attribute ((visibility)) and/or #pragma GCC visibility to tell the
 compiler which extern declarations should be treated as hidden."

Jan

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      reply	other threads:[~2019-12-13 21:02 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-12 18:27 [Xen-devel] [XEN PATCH 0/8] xen: Kconfig update with few extra Anthony PERARD
2019-12-12 18:27 ` [Xen-devel] [XEN PATCH 1/8] Config.mk: Remove unused setvar_dir macro Anthony PERARD
2019-12-12 18:30   ` Andrew Cooper
2019-12-13 14:51     ` Anthony PERARD
2019-12-12 18:27 ` [Xen-devel] [XEN PATCH 2/8] Config.mk: Remove stray comment Anthony PERARD
2019-12-12 18:32   ` Andrew Cooper
2019-12-13 15:16     ` Anthony PERARD
2019-12-12 18:27 ` [Xen-devel] [XEN PATCH 3/8] xen: Update Kconfig to Linux v5.4 Anthony PERARD
2019-12-12 18:45   ` Andrew Cooper
2019-12-13 15:31     ` Anthony PERARD
2019-12-13 11:05   ` Jan Beulich
2019-12-13 15:49     ` Anthony PERARD
2019-12-13 16:59       ` Jan Beulich
2019-12-13 19:17         ` Andrew Cooper
2019-12-16 10:16           ` Jan Beulich
2019-12-16 14:01             ` Anthony PERARD
2019-12-16 15:55               ` Jan Beulich
2019-12-16 16:34                 ` Anthony PERARD
2019-12-12 18:27 ` [Xen-devel] [XEN PATCH 4/8] xen: Have Kconfig check $(CC)'s version Anthony PERARD
2019-12-12 18:56   ` Andrew Cooper
2019-12-13 16:08     ` Anthony PERARD
2019-12-12 18:27 ` [Xen-devel] [XEN PATCH 5/8] xen: Import cc-ifversion from Kbuild Anthony PERARD
2019-12-12 18:56   ` Andrew Cooper
2019-12-12 18:27 ` [Xen-devel] [XEN PATCH 6/8] xen: Move CONFIG_INDIRECT_THUNK to Kconfig Anthony PERARD
2019-12-12 18:58   ` Andrew Cooper
2019-12-13 11:13   ` Jan Beulich
2019-12-13 12:18     ` Anthony PERARD
2019-12-13 12:27       ` Jan Beulich
2020-02-18 16:43       ` Jan Beulich
2020-02-18 17:13         ` Anthony PERARD
2020-02-19  7:55           ` Jan Beulich
2019-12-12 18:27 ` [Xen-devel] [XEN PATCH 7/8] xen: Use $(CONFIG_CC_IS_CLANG) instead of $(clang) in Makefile Anthony PERARD
2019-12-12 19:00   ` Andrew Cooper
2019-12-13 14:37     ` Anthony PERARD
2019-12-12 18:27 ` [Xen-devel] [XEN PATCH 8/8] xen: Move GCC_HAS_VISIBILITY_ATTRIBUTE to Kconfig and common Anthony PERARD
2019-12-12 19:04   ` Andrew Cooper
2019-12-13 11:27     ` Jan Beulich [this message]

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