Re: [PATCH] kexec: derive purgatory entry from symbol

[Li Chen <me@linux.beauty>]

Hi Baoquan,

 > Hi Li Chen,
 > 
 > On 01/20/26 at 08:40pm, Li Chen wrote:
 > > kexec_load_purgatory() derives image->start by locating e_entry inside an
 > > SHF_EXECINSTR section. If the purgatory object contains multiple executable
 > > sections with overlapping sh_addr, the entrypoint check can match more than
 > > once and trigger a WARN.
 > > 
 > > Derive the entry section from the purgatory_start symbol when present and
 > > compute image->start from its final placement. Keep the existing e_entry
 > > fallback for purgatories that do not expose the symbol.
 > > 
 > > WARNING: kernel/kexec_file.c:1009 at kexec_load_purgatory+0x395/0x3c0, CPU#10: kexec/1784
 > > Call Trace:
 > >  <TASK>
 > >  bzImage64_load+0x133/0xa00
 > >  __do_sys_kexec_file_load+0x2b3/0x5c0
 > >  do_syscall_64+0x81/0x610
 > >  entry_SYSCALL_64_after_hwframe+0x76/0x7e
 > > 
 > > Fixes: 8652d44f466a ("kexec: support purgatories with .text.hot sections")
 > > Signed-off-by: Li Chen <me@linux.beauty>
 > 
 > Thanks for fixing the issue. Could you tell how we can trigger this
 > issue so that I can reproduce it?
 > 
 > > ---
 > >  kernel/kexec_file.c | 24 ++++++++++++++++++++++--
 > >  1 file changed, 22 insertions(+), 2 deletions(-)
 > > 
 > > diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
 > > index 3f1d6c4e8ff2..d3c68c6b4bbc 100644
 > > --- a/kernel/kexec_file.c
 > > +++ b/kernel/kexec_file.c
 > > @@ -880,6 +880,8 @@ static int kexec_calculate_store_digests(struct kimage *image)
 > >  }
 > >  
 > >  #ifdef CONFIG_ARCH_SUPPORTS_KEXEC_PURGATORY
 > > +static const Elf_Sym * kexec_purgatory_find_symbol(struct purgatory_info *pi,
 > > +                  const char *name);
 > 
 > Here, is it better to move the whole function body of
 > kexec_purgatory_find_symbol() here so that kexec_purgatory_setup_sechdrs()
 > can see it too?
 > 
 > Other than the concerns about how to reproducing and above one, this
 > patch looks good to me.

Thanks for the review.

For reference, I observed this WARN on x86_64 with linux-next tag
next-20260106 and the savedefconfig included below. Toolchain was GCC
15.2.1 and binutils 2.45.1.

The WARN is triggered in the kexec_file_load path (kexec -s -l), during
purgatory load/relocation. No kexec -e is required.

command I used:

  sudo kexec -s -l /boot/vmlinuz-$(uname -r) \
    --initrd=/boot/initramfs-$(uname -r).img \
    --append="$(cat /proc/cmdline | sed -E \"s/(^| )BOOT_IMAGE=[^ ]+//g\")"

Regarding kexec_purgatory_find_symbol(), agreed; I will move the helper
body above kexec_purgatory_setup_sechdrs() in v2 to avoid the forward
declaration.

kernel config:
https://gist.github.com/FirstLoveLife/b0e7c7da7146f1ba63167b76cb10683a

Regards,
Li​