From mboxrd@z Thu Jan 1 00:00:00 1970 From: Naveen N. Rao Date: Thu, 19 May 2022 14:58:20 +0530 Subject: [PATCH] kexec_file: Drop weak attribute from arch_kexec_apply_relocations[_add] In-Reply-To: References: <20220518181828.645877-1-naveen.n.rao@linux.vnet.ibm.com> <87ee0q7b92.fsf@email.froward.int.ebiederm.org> Message-ID: <1652951723.o9i6ngwfda.naveen@linux.ibm.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: kexec@lists.infradead.org Baoquan He wrote: > Hi Eric, > > On 05/18/22 at 04:59pm, Eric W. Biederman wrote: >> "Naveen N. Rao" writes: >> >> > Since commit d1bcae833b32f1 ("ELF: Don't generate unused section >> > symbols") [1], binutils (v2.36+) started dropping section symbols that >> > it thought were unused. This isn't an issue in general, but with >> > kexec_file.c, gcc is placing kexec_arch_apply_relocations[_add] into a >> > separate .text.unlikely section and the section symbol ".text.unlikely" >> > is being dropped. Due to this, recordmcount is unable to find a non-weak >> > symbol in .text.unlikely to generate a relocation record against. >> > >> > Address this by dropping the weak attribute from these functions: >> > - arch_kexec_apply_relocations() is not overridden by any architecture >> > today, so just drop the weak attribute. >> > - arch_kexec_apply_relocations_add() is only overridden by x86 and s390. >> > Retain the function prototype for those and move the weak >> > implementation into the header as a static inline for other >> > architectures. >> > >> > [1] https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=d1bcae833b32f1 >> >> Any chance you can also get machine_kexec_post_load, >> crash_free_reserved_phys_range, arch_kexec_protect_protect_crashkres, >> arch_kexec_unprotect_crashkres, arch_kexec_kernel_image_probe, >> arch_kexec_kernel_image_probe, arch_kimage_file_post_load_cleanup, >> arch_kexec_kernel_verify_sig, and arch_kexec_locate_mem_hole as well. I've posted a v2 that uses the approach suggested by Michael, and something that was in use in kexec already. If you are ok with that approach, I will take a stab at converting the rest of the functions that are marked __weak. >> >> That is everything in kexec that uses a __weak symbol. If we can't >> count on them working we might as well just get rid of the rest >> preemptively. > > Is there a new rule that __weak is not suggested in kernel any more? > Please help provide a pointer if yes, so that I can learn that. I'm not aware of a move away from __weak in the kernel, in general. Steven doesn't prefer it for ftrace, and other maintainers may have a preference. > > In my mind, __weak is very simple and clear as a mechanism to add > ARCH related functionality. Notwithstanding the ftrace issue, the other caveat with __weak functions are that they still make it into the final vmlinux even if they are overridden. That is, you will have instructions from both the __weak variant as well as from the overridden variant in the final vmlinux, which can add up if the weak variants are non-trivial. - Naveen