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

[Pingfan Liu <piliu@redhat.com>]

On Mon, Sep 01, 2025 at 04:31:07PM +0200, Philipp Rudo wrote:
> 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.
> 

Yes, it should be dropped. Once I placed the declaration of
elf_find_symbol() here, and later moved it behind.


Thanks,

Pingfan

> 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)
>