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From: Segher Boessenkool <segher@kernel.crashing.org>
To: David Laight <David.Laight@ACULAB.COM>
Cc: "'Daniel Axtens'" <dja@axtens.net>,
	Lakshmi Ramasubramanian <nramas@linux.microsoft.com>,
	"robh@kernel.org" <robh@kernel.org>,
	"dan.carpenter@oracle.com" <dan.carpenter@oracle.com>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	"kbuild-all@lists.01.org" <kbuild-all@lists.01.org>,
	"bauerman@linux.ibm.com" <bauerman@linux.ibm.com>,
	"lkp@intel.com" <lkp@intel.com>
Subject: Re: [PATCH] powerpc: Initialize local variable fdt to NULL in elf64_load()
Date: Thu, 22 Apr 2021 11:54:37 -0500	[thread overview]
Message-ID: <20210422165437.GA27473@gate.crashing.org> (raw)
In-Reply-To: <3e6b31d92d5042d982daeb989e49299e@AcuMS.aculab.com>

On Thu, Apr 22, 2021 at 08:05:27AM +0000, David Laight wrote:
> > (Does anyone - and by anyone I mean any large distro - compile with
> > local variables inited by the compiler?)
> 
> There are compilers that initialise locals to zero for 'debug' builds
> and leave the 'random' for optimised 'release' builds.
> Lets not test what we are releasing!

Yeah, that's the worst of all possible worlds.

> I also think there is a new option to gcc (or clang?) to initialise
> on-stack structures and arrays to ensure garbage isn't passed.
> That seems to be a horrid performance hit!
> Especially in userspace where large stack allocations are almost free.
> 
> Any auto-initialise ought to be with a semi-random value
> (especially not zero) so that it is never right and doesn't
> lead to lazy coding.

Many compilers did something like this, decades ago -- for debug builds.


Segher

WARNING: multiple messages have this Message-ID (diff)
From: Segher Boessenkool <segher@kernel.crashing.org>
To: David Laight <David.Laight@ACULAB.COM>
Cc: "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	"kbuild-all@lists.01.org" <kbuild-all@lists.01.org>,
	"lkp@intel.com" <lkp@intel.com>,
	"robh@kernel.org" <robh@kernel.org>,
	Lakshmi Ramasubramanian <nramas@linux.microsoft.com>,
	"bauerman@linux.ibm.com" <bauerman@linux.ibm.com>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	"dan.carpenter@oracle.com" <dan.carpenter@oracle.com>,
	'Daniel Axtens' <dja@axtens.net>
Subject: Re: [PATCH] powerpc: Initialize local variable fdt to NULL in elf64_load()
Date: Thu, 22 Apr 2021 11:54:37 -0500	[thread overview]
Message-ID: <20210422165437.GA27473@gate.crashing.org> (raw)
In-Reply-To: <3e6b31d92d5042d982daeb989e49299e@AcuMS.aculab.com>

On Thu, Apr 22, 2021 at 08:05:27AM +0000, David Laight wrote:
> > (Does anyone - and by anyone I mean any large distro - compile with
> > local variables inited by the compiler?)
> 
> There are compilers that initialise locals to zero for 'debug' builds
> and leave the 'random' for optimised 'release' builds.
> Lets not test what we are releasing!

Yeah, that's the worst of all possible worlds.

> I also think there is a new option to gcc (or clang?) to initialise
> on-stack structures and arrays to ensure garbage isn't passed.
> That seems to be a horrid performance hit!
> Especially in userspace where large stack allocations are almost free.
> 
> Any auto-initialise ought to be with a semi-random value
> (especially not zero) so that it is never right and doesn't
> lead to lazy coding.

Many compilers did something like this, decades ago -- for debug builds.


Segher

  parent reply	other threads:[~2021-04-22 17:00 UTC|newest]

Thread overview: 63+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-15 19:14 [PATCH] powerpc: Initialize local variable fdt to NULL in elf64_load() Lakshmi Ramasubramanian
2021-04-15 19:18 ` Lakshmi Ramasubramanian
2021-04-15 19:18   ` Lakshmi Ramasubramanian
2021-04-15 19:18   ` Lakshmi Ramasubramanian
2021-04-16  6:44   ` Daniel Axtens
2021-04-16  6:44     ` Daniel Axtens
2021-04-16  6:44     ` Daniel Axtens
2021-04-16  7:00     ` Christophe Leroy
2021-04-16  7:00       ` Christophe Leroy
2021-04-16  8:09       ` Dan Carpenter
2021-04-16  8:09         ` Dan Carpenter
2021-04-16  8:09         ` Dan Carpenter
2021-04-16 12:19         ` Michael Ellerman
2021-04-16 12:19           ` Michael Ellerman
2021-04-16  7:40     ` Dan Carpenter
2021-04-16  7:40       ` Dan Carpenter
2021-04-16  7:40       ` Dan Carpenter
2021-04-16  9:05     ` Michael Ellerman
2021-04-16  9:05       ` Michael Ellerman
2021-04-16 14:37       ` Lakshmi Ramasubramanian
2021-04-16 14:37         ` Lakshmi Ramasubramanian
2021-04-19 23:30         ` Michael Ellerman
2021-04-19 23:30           ` Michael Ellerman
2021-04-20  1:33           ` Lakshmi Ramasubramanian
2021-04-20  1:33             ` Lakshmi Ramasubramanian
2021-04-20  5:00           ` Dan Carpenter
2021-04-20  5:00             ` Dan Carpenter
2021-04-20  5:00             ` Dan Carpenter
2021-04-20  5:20             ` Lakshmi Ramasubramanian
2021-04-20  5:20               ` Lakshmi Ramasubramanian
2021-04-20  5:20               ` Lakshmi Ramasubramanian
2021-04-20 13:06               ` Rob Herring
2021-04-20 13:06                 ` Rob Herring
2021-04-20 13:06                 ` Rob Herring
2021-04-20 14:42                 ` Lakshmi Ramasubramanian
2021-04-20 14:42                   ` Lakshmi Ramasubramanian
2021-04-20 14:42                   ` Lakshmi Ramasubramanian
2021-04-20 15:04                   ` Lakshmi Ramasubramanian
2021-04-20 15:04                     ` Lakshmi Ramasubramanian
2021-04-20 15:04                     ` Lakshmi Ramasubramanian
2021-04-20 15:47                     ` Rob Herring
2021-04-20 15:47                       ` Rob Herring
2021-04-20 15:47                       ` Rob Herring
2021-04-20 15:55                       ` Lakshmi Ramasubramanian
2021-04-20 15:55                         ` Lakshmi Ramasubramanian
2021-04-20 15:55                         ` Lakshmi Ramasubramanian
2021-04-22  2:21     ` Daniel Axtens
2021-04-22  2:21       ` Daniel Axtens
2021-04-22  2:21       ` Daniel Axtens
2021-04-22  8:05       ` David Laight
2021-04-22  8:05         ` David Laight
2021-04-22  9:34         ` Dan Carpenter
2021-04-22  9:34           ` Dan Carpenter
2021-04-22  9:34           ` Dan Carpenter
2021-04-22 16:54         ` Segher Boessenkool [this message]
2021-04-22 16:54           ` Segher Boessenkool
2021-04-23 13:50       ` Michael Ellerman
2021-04-23 13:50         ` Michael Ellerman
2021-04-23 14:42         ` David Laight
2021-04-23 14:42           ` David Laight
2021-04-23 15:11           ` Rob Herring
2021-04-23 15:11             ` Rob Herring
2021-04-23 15:11             ` Rob Herring

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