linux-kernel - Re: [PATCH v15 1/7] crash: move crash_prepare_elf64

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Date:   Mon, 9 Jan 2023 10:35:46 +0530
From:   Sourabh Jain <sourabhjain@...ux.ibm.com>
To:     Eric DeVolder <eric.devolder@...cle.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        kexec@...ts.infradead.org, ebiederm@...ssion.com,
        dyoung@...hat.com, bhe@...hat.com, vgoyal@...hat.com
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com,
        nramas@...ux.microsoft.com, thomas.lendacky@....com,
        robh@...nel.org, efault@....de, rppt@...nel.org, david@...hat.com,
        konrad.wilk@...cle.com, boris.ostrovsky@...cle.com
Subject: Re: [PATCH v15 1/7] crash: move crash_prepare_elf64_headers()


On 09/12/22 21:06, Eric DeVolder wrote:
> At the outcome of this patch set, the crash_prepare_elf64_headers()
> is utilized on both the kexec_file_load() and kexec_load() paths. As
> such, need to move this function out of kexec_file.c and into a
> common location crash_core.c.
>
> No functionality change.
>
> Signed-off-by: Eric DeVolder <eric.devolder@...cle.com>
> Acked-by: Baoquan He <bhe@...hat.com>
> ---
>   kernel/crash_core.c | 100 ++++++++++++++++++++++++++++++++++++++++++++
>   kernel/kexec_file.c |  99 -------------------------------------------
>   2 files changed, 100 insertions(+), 99 deletions(-)
>
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index a0eb4d5cf557..46c160d14045 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -10,6 +10,7 @@
>   #include <linux/utsname.h>
>   #include <linux/vmalloc.h>
>   #include <linux/sizes.h>
> +#include <linux/kexec.h>
>   
>   #include <asm/page.h>
>   #include <asm/sections.h>
> @@ -314,6 +315,105 @@ static int __init parse_crashkernel_dummy(char *arg)
>   }
>   early_param("crashkernel", parse_crashkernel_dummy);
>   
> +int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
> +			  void **addr, unsigned long *sz)
> +{
> +	Elf64_Ehdr *ehdr;
> +	Elf64_Phdr *phdr;
> +	unsigned long nr_cpus = num_possible_cpus(), nr_phdr, elf_sz;
> +	unsigned char *buf;
> +	unsigned int cpu, i;
> +	unsigned long long notes_addr;
> +	unsigned long mstart, mend;
> +
> +	/* extra phdr for vmcoreinfo ELF note */
> +	nr_phdr = nr_cpus + 1;
> +	nr_phdr += mem->nr_ranges;
> +
> +	/*
> +	 * kexec-tools creates an extra PT_LOAD phdr for kernel text mapping
> +	 * area (for example, ffffffff80000000 - ffffffffa0000000 on x86_64).
> +	 * I think this is required by tools like gdb. So same physical
> +	 * memory will be mapped in two ELF headers. One will contain kernel
> +	 * text virtual addresses and other will have __va(physical) addresses.
> +	 */
> +
> +	nr_phdr++;
> +	elf_sz = sizeof(Elf64_Ehdr) + nr_phdr * sizeof(Elf64_Phdr);
> +	elf_sz = ALIGN(elf_sz, ELF_CORE_HEADER_ALIGN);
Seems like above function is out of CONFIG_KEXEC_FILE but some of the
structure/attributes like crash_mem and ELF_CORE_HEADER_ALIGN are
still defined under CONFIG_KEXEC_FILE (look for include/linux/kexec.h).

This leads to kernel build issue when CONFIG_KEXEC_FILE is disabled.

Thanks,
Sourabh Jain