Re: [PATCHv5 08/12] kexec: Factor out routine to find a symbol in ELF

[Philipp Rudo <prudo@redhat.com>]

On Tue, 19 Aug 2025 09:24:24 +0800
Pingfan Liu <piliu@redhat.com> wrote:

> The routine to search a symbol in ELF can be shared, so split it out.
> 
> Signed-off-by: Pingfan Liu <piliu@redhat.com>
> Cc: Baoquan He <bhe@redhat.com>
> Cc: Dave Young <dyoung@redhat.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Philipp Rudo <prudo@redhat.com>
> To: kexec@lists.infradead.org
> ---
>  include/linux/kexec.h |  8 ++++
>  kernel/kexec_file.c   | 86 +++++++++++++++++++++++--------------------
>  2 files changed, 54 insertions(+), 40 deletions(-)
> 
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index 8f7322c932fb5..2998d8da09d86 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -23,6 +23,10 @@
>  #include <uapi/linux/kexec.h>
>  #include <linux/verification.h>
>  
> +#if defined(CONFIG_ARCH_SUPPORTS_KEXEC_PURGATORY) || defined(CONFIG_KEXEC_PE_IMAGE)
> +#include <linux/module.h>
> +#endif
> +

What is linux/module.h used for? Plus module.h already gets included a
little below, when CONFIG_KEXEC_CORE is set, which should always be the
case for those two configs.

Thanks
Philipp

>  extern note_buf_t __percpu *crash_notes;
>  
>  #ifdef CONFIG_CRASH_DUMP
> @@ -550,6 +554,10 @@ void set_kexec_sig_enforced(void);
>  static inline void set_kexec_sig_enforced(void) {}
>  #endif
>  
> +#if defined(CONFIG_ARCH_SUPPORTS_KEXEC_PURGATORY) || defined(CONFIG_KEXEC_PE_IMAGE)
> +const Elf_Sym *elf_find_symbol(const Elf_Ehdr *ehdr, const char *name);
> +#endif
> +
>  #endif /* !defined(__ASSEBMLY__) */
>  
>  #endif /* LINUX_KEXEC_H */
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index 4780d8aae24e7..137049e7e2410 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -880,6 +880,51 @@ static int kexec_calculate_store_digests(struct kimage *image)
>  	return ret;
>  }
>  
> +#if defined(CONFIG_ARCH_SUPPORTS_KEXEC_PURGATORY) || defined(CONFIG_KEXEC_PE_IMAGE)
> +const Elf_Sym *elf_find_symbol(const Elf_Ehdr *ehdr, const char *name)
> +{
> +	const Elf_Shdr *sechdrs;
> +	const Elf_Sym *syms;
> +	const char *strtab;
> +	int i, k;
> +
> +	sechdrs = (void *)ehdr + ehdr->e_shoff;
> +
> +	for (i = 0; i < ehdr->e_shnum; i++) {
> +		if (sechdrs[i].sh_type != SHT_SYMTAB)
> +			continue;
> +
> +		if (sechdrs[i].sh_link >= ehdr->e_shnum)
> +			/* Invalid strtab section number */
> +			continue;
> +		strtab = (void *)ehdr + sechdrs[sechdrs[i].sh_link].sh_offset;
> +		syms = (void *)ehdr + sechdrs[i].sh_offset;
> +
> +		/* Go through symbols for a match */
> +		for (k = 0; k < sechdrs[i].sh_size/sizeof(Elf_Sym); k++) {
> +			if (ELF_ST_BIND(syms[k].st_info) != STB_GLOBAL)
> +				continue;
> +
> +			if (strcmp(strtab + syms[k].st_name, name) != 0)
> +				continue;
> +
> +			if (syms[k].st_shndx == SHN_UNDEF ||
> +			    syms[k].st_shndx >= ehdr->e_shnum) {
> +				pr_debug("Symbol: %s has bad section index %d.\n",
> +						name, syms[k].st_shndx);
> +				return NULL;
> +			}
> +
> +			/* Found the symbol we are looking for */
> +			return &syms[k];
> +		}
> +	}
> +
> +	return NULL;
> +}
> +
> +#endif
> +
>  #ifdef CONFIG_ARCH_SUPPORTS_KEXEC_PURGATORY
>  /*
>   * kexec_purgatory_setup_kbuf - prepare buffer to load purgatory.
> @@ -1137,49 +1182,10 @@ int kexec_load_purgatory(struct kimage *image, struct kexec_buf *kbuf)
>  static const Elf_Sym *kexec_purgatory_find_symbol(struct purgatory_info *pi,
>  						  const char *name)
>  {
> -	const Elf_Shdr *sechdrs;
> -	const Elf_Ehdr *ehdr;
> -	const Elf_Sym *syms;
> -	const char *strtab;
> -	int i, k;
> -
>  	if (!pi->ehdr)
>  		return NULL;
>  
> -	ehdr = pi->ehdr;
> -	sechdrs = (void *)ehdr + ehdr->e_shoff;
> -
> -	for (i = 0; i < ehdr->e_shnum; i++) {
> -		if (sechdrs[i].sh_type != SHT_SYMTAB)
> -			continue;
> -
> -		if (sechdrs[i].sh_link >= ehdr->e_shnum)
> -			/* Invalid strtab section number */
> -			continue;
> -		strtab = (void *)ehdr + sechdrs[sechdrs[i].sh_link].sh_offset;
> -		syms = (void *)ehdr + sechdrs[i].sh_offset;
> -
> -		/* Go through symbols for a match */
> -		for (k = 0; k < sechdrs[i].sh_size/sizeof(Elf_Sym); k++) {
> -			if (ELF_ST_BIND(syms[k].st_info) != STB_GLOBAL)
> -				continue;
> -
> -			if (strcmp(strtab + syms[k].st_name, name) != 0)
> -				continue;
> -
> -			if (syms[k].st_shndx == SHN_UNDEF ||
> -			    syms[k].st_shndx >= ehdr->e_shnum) {
> -				pr_debug("Symbol: %s has bad section index %d.\n",
> -						name, syms[k].st_shndx);
> -				return NULL;
> -			}
> -
> -			/* Found the symbol we are looking for */
> -			return &syms[k];
> -		}
> -	}
> -
> -	return NULL;
> +	return elf_find_symbol(pi->ehdr, name);
>  }
>  
>  void *kexec_purgatory_get_symbol_addr(struct kimage *image, const char *name)