From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [PATCH] Extract initrd free logic from arch-specific code. References: <20180325221853.10839-1-shea@shealevy.com> <20180328152714.6103-1-shea@shealevy.com> <05620fee-e8b5-0668-77b8-da073dc78c40@landley.net> <20180328164813.GA3888@n2100.armlinux.org.uk> <20180328221401.GA14084@n2100.armlinux.org.uk> From: Rob Landley Message-ID: Date: Thu, 29 Mar 2018 11:39:24 -0500 MIME-Version: 1.0 In-Reply-To: <20180328221401.GA14084@n2100.armlinux.org.uk> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit To: Russell King - ARM Linux Cc: Shea Levy , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, Christoph Hellwig , Richard Henderson , Ivan Kokshaysky , Matt Turner , Vineet Gupta , Catalin Marinas , Will Deacon , Mark Salter , Aurelien Jacquiot , Mikael Starvik , Jesper Nilsson , Yoshinori Sato , Richard Kuo , Tony Luck , Fenghua Yu , Geert Uytterhoeven , James Hogan , Michal Simek , Ralf Baechle , David Howells , Ley Foon Tan , Jonas Bonn , Stefan Kristiansson , Stafford Horne , "James E.J. Bottomley" , Helge Deller , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Palmer Dabbelt , Albert Ou , Martin Schwidefsky , Heiko Carstens , Chen Liqin , Lennox Wu , Rich Felker , "David S. Miller" , Jeff Dike , Richard Weinberger , Guan Xuetao , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, Chris Zankel , Max Filippov , Kate Stewart , Greg Kroah-Hartman , Philippe Ombredanne , Eugeniy Paltsev , Al Viro , Vladimir Murzin , Linus Walleij , Michal Hocko , Andrew Morton , Sudip Mukherjee , Marc Zyngier , Rob Herring , Kees Cook , Vlastimil Babka , Balbir Singh , Christophe Leroy , Joe Perches , Oliver O'Halloran , Dan Williams , Wei Yang , =?UTF-8?Q?Christian_K=c3=b6nig?= , Arnd Bergmann , Deepa Dinamani , Daniel Thompson , Florian Fainelli , linux-alpha@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, adi-buildroot-devel@lists.sourceforge.net, linux-c6x-dev@linux-c6x.org, linux-cris-kernel@axis.com, uclinux-h8-devel@lists.sourceforge.jp, linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-metag@vger.kernel.org, linux-mips@linux-mips.org, linux-am33-list@redhat.com, nios2-dev@lists.rocketboards.org, openrisc@lists.librecores.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, user-mode-linux-devel@lists.sourceforge.net, user-mode-linux-user@lists.sourceforge.net, linux-xtensa@linux-xtensa.org List-ID: On 03/28/2018 05:14 PM, Russell King - ARM Linux wrote: > On Wed, Mar 28, 2018 at 02:04:22PM -0500, Rob Landley wrote: >> >> >> On 03/28/2018 11:48 AM, Russell King - ARM Linux wrote: >>> On Wed, Mar 28, 2018 at 10:58:51AM -0500, Rob Landley wrote: >>>> On 03/28/2018 10:26 AM, Shea Levy wrote: >>>>> Now only those architectures that have custom initrd free requirements >>>>> need to define free_initrd_mem. >>>> ... >>>>> --- a/arch/arc/mm/init.c >>>>> +++ b/arch/arc/mm/init.c >>>>> @@ -229,10 +229,3 @@ void __ref free_initmem(void) >>>>> { >>>>> free_initmem_default(-1); >>>>> } >>>>> - >>>>> -#ifdef CONFIG_BLK_DEV_INITRD >>>>> -void __init free_initrd_mem(unsigned long start, unsigned long end) >>>>> -{ >>>>> - free_reserved_area((void *)start, (void *)end, -1, "initrd"); >>>>> -} >>>>> -#endif >>>>> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig >>>>> index 3f972e83909b..19d1c5594e2d 100644 >>>>> --- a/arch/arm/Kconfig >>>>> +++ b/arch/arm/Kconfig >>>>> @@ -47,6 +47,7 @@ config ARM >>>>> select HARDIRQS_SW_RESEND >>>>> select HAVE_ARCH_AUDITSYSCALL if (AEABI && !OABI_COMPAT) >>>>> select HAVE_ARCH_BITREVERSE if (CPU_32v7M || CPU_32v7) && !CPU_32v6 >>>>> + select HAVE_ARCH_FREE_INITRD_MEM >>>>> select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL && !CPU_ENDIAN_BE32 && MMU >>>>> select HAVE_ARCH_KGDB if !CPU_ENDIAN_BE32 && MMU >>>>> select HAVE_ARCH_MMAP_RND_BITS if MMU >>>> >>>> Isn't this why weak symbols were invented? >>> >>> Weak symbols means that we end up with both the weakly-referenced code >>> and the arch code in the kernel image. That's fine if the weak code >>> is small. >> >> The kernel's been able to build with link time garbage collection since 2016: >> >> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b67067f1176d >> >> Wouldn't that remove the unused one? > > Probably, if anyone bothered to use that, which they don't. > > LD_DEAD_CODE_DATA_ELIMINATION is a symbol without a prompt, and from > what I can see, nothing selects it. Therefore, the symbol is always > disabled, and so the feature never gets used in mainline kernels. It looks like there are per-architecture linker scripts that need to be updated? So if an architecture supports it, it's always done (well, it probes for the toolchain supporting the flag). And if the architecture doesn't support it, the linker script needs to be updated to mark sections with "I know nothing seems to reference this at the ELF level but keep it anyway, we're pulling an assembly trick". > Brings up the obvious question - why is it there if it's completely > unused? (Maybe to cause confusion, and allowing a justification > for __weak ?) Presumably it will become the default on architectures as their linker scripts are converted. Once they're all converted the config symbol can go away. (Given the move to requiring gcc 4.7 or whatever it is, there can't be an architecture depending on a toolchain that _doesn't_ support it after that point. I doubt you can pair gcc 4.7 with a >12 year old binutils and expect good things...) Rob