linux-kernel - Re: Edited kexec_load(2) [kexec_file

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Message-ID: <CAKgNAkjBBRmcpu8DuaGCCRhvXP_AFotK5xrHx2HaR6g_8omULw@mail.gmail.com>
Date:	Thu, 29 Jan 2015 06:39:56 +0100
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Scot Doyle <lkml14@...tdoyle.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>,
	lkml <linux-kernel@...r.kernel.org>,
	"linux-man@...r.kernel.org" <linux-man@...r.kernel.org>,
	Kexec Mailing List <kexec@...ts.infradead.org>,
	Andy Lutomirski <luto@...capital.net>,
	Dave Young <dyoung@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: Edited kexec_load(2) [kexec_file_load()] man page for review

On 29 January 2015 at 02:27, Scot Doyle <lkml14@...tdoyle.com> wrote:
> On Wed, 28 Jan 2015, Vivek Goyal wrote:
>> On Wed, Jan 28, 2015 at 10:10:59PM +0000, Scot Doyle wrote:
>> > On Wed, 28 Jan 2015, Vivek Goyal wrote:
>> > > On Wed, Jan 28, 2015 at 09:14:03PM +0000, Scot Doyle wrote:
>> > > > When I tested, kexec_file_load required CONFIG_RELOCATABLE. Is the same
>> > > > true for kexec_load? Would it make sense to note this in the man pages
>> > > > along with the need for CONFIG_KEXEC_FILE, etc? Or as an error message?
>> > >
>> > > Hmm.., I can't see an explicity dependency between RELOCATABLE and
>> > > KEXEC. Both KEXEC and KEXEC_FILE should be able to load a kernel
>> > > even if it had RELOCATABLE=n.
>> > >
>> > > Just that kernel will run from the address it has been built for.
>> > >
>> > > Thanks
>> > > Vivek
>> >
>> > Confusing, right? kexec_file_load returns -ENOEXEC and dmesg says
>> > "kexec-bzImage64: XLF_CAN_BE_LOADED_ABOVE_4G is not set." which leads to
>> > arch/x86/boot/header.S line 396:
>> >
>> > #if defined(CONFIG_RELOCATABLE) && defined(CONFIG_X86_64)
>> >    /* kernel/boot_param/ramdisk could be loaded above 4g */
>> > # define XLF1 XLF_CAN_BE_LOADED_ABOVE_4G
>> > #else
>> > # define XLF1 0
>> > #endif
>>
>> Ah, this one. Actually generic kexec file loading implementation does not
>> impose this restriction. It is the image specific loader part which
>> decides what kind of bzImage it can load.
>>
>> Current implementation (kexec-bzimage64.c), is only supporting loading
>> bzImages which are 64bit and can be loaded above 4G. This simplifies
>> the implementation of loader.
>>
>> But there is nothing which prevents one from implementing other image
>> loaders.
>>
>> So instead of saying that kexec_file_load() depends on CONFIG_RELOCATABLE,
>> it might be better to say in man page that currently this system call
>> supports only loading a bzImage which is 64bit and which can be loaded
>> above 4G too.
>>
>> Thanks
>> Vivek
>
> Thanks, I agree, and think it would make sense to list them as part of the
> page's ENOEXEC error.

Scott, could you then phras a couple of sentences that capture thge
details, so I can add it to the ENOEXEC error?

Thanks,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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