Re: [RFC 00/31] objtool, livepatch: Livepatch module generation

[Joe Lawrence <joe.lawrence@redhat.com>]

On Fri, Sep 06, 2024 at 10:00:08AM -0700, Josh Poimboeuf wrote:
> On Fri, Sep 06, 2024 at 09:56:06AM -0400, Joe Lawrence wrote:
> > In the case of klp-diff.c, adding #include <string.h> will provide the
> > memmem prototype.  For both files, I needed to #define _GNU_SOURCE for
> > that prototype though.
> > 
> > For the other complaint, I just set struct instruction *dest_insn = NULL
> > at the top of the for loop, but perhaps the code could be refactored to
> > clarify the situation to the compiler if you prefer not to do that.
> 
> Thanks!  I'll get these fixed up.
> 

Also, with the workarounds mentioned above, the two you sent to Song,
and the same .config I attached in the first email, I get the following
error when trying to build the canonical /proc/cmdline example:

  $ cat cmdline-string.patch 
  diff --git a/fs/proc/cmdline.c b/fs/proc/cmdline.c
  index a6f76121955f..2bcaf9ec6f78 100644
  --- a/fs/proc/cmdline.c
  +++ b/fs/proc/cmdline.c
  @@ -7,8 +7,7 @@
   
   static int cmdline_proc_show(struct seq_file *m, void *v)
   {
  -       seq_puts(m, saved_command_line);
  -       seq_putc(m, '\n');
  +       seq_printf(m, "%s kpatch=1", saved_command_line);
          return 0;
   }


  $ ./scripts/livepatch/klp-build ./cmdline-string.patch 2>&1 | tee build2.out
  - klp-build: building original kernel
  vmlinux.o: warning: objtool: init_espfix_bsp+0xab: unreachable instruction
  vmlinux.o: warning: objtool: init_espfix_ap+0x50: unreachable instruction
  vmlinux.o: warning: objtool: syscall_init+0xca: unreachable instruction
  vmlinux.o: warning: objtool: sync_core_before_usermode+0xf: unreachable instruction
  vmlinux.o: warning: objtool: sync_core_before_usermode+0xf: unreachable instruction
  vmlinux.o: warning: objtool: tc_wrapper_init+0x16: unreachable instruction
  vmlinux.o: warning: objtool: pvh_start_xen+0x50: relocation to !ENDBR: pvh_start_xen+0x57
  - klp-build: building patched kernel
  vmlinux.o: warning: objtool: init_espfix_bsp+0xab: unreachable instruction
  vmlinux.o: warning: objtool: init_espfix_ap+0x50: unreachable instruction
  vmlinux.o: warning: objtool: syscall_init+0xca: unreachable instruction
  vmlinux.o: warning: objtool: sync_core_before_usermode+0xf: unreachable instruction
  vmlinux.o: warning: objtool: sync_core_before_usermode+0xf: unreachable instruction
  vmlinux.o: warning: objtool: tc_wrapper_init+0x16: unreachable instruction
  vmlinux.o: warning: objtool: pvh_start_xen+0x50: relocation to !ENDBR: pvh_start_xen+0x57
  - klp-build: diffing objects
  kvm.o: added: __UNIQUE_ID_nop_644
  kvm.o: added: __UNIQUE_ID_nop_645
  kvm.o: added: __UNIQUE_ID_nop_646
  kvm.o: added: __UNIQUE_ID_nop_647
  kvm.o: added: __UNIQUE_ID_nop_648
  kvm.o: added: __UNIQUE_ID_nop_649
  kvm.o: added: __UNIQUE_ID_nop_650
  kvm.o: added: __UNIQUE_ID_nop_651
  kvm.o: added: __UNIQUE_ID_nop_652
  vmlinux.o: changed: cmdline_proc_show
  - klp-build: building patch module
  make[2]: /bin/sh: Argument list too long
  make[2]: *** [scripts/Makefile.build:253: /home/jolawren/src/linux/klp-tmp/out/livepatch.mod] Error 127
  make[1]: *** [/home/jolawren/src/linux/Makefile:1943: /home/jolawren/src/linux/klp-tmp/out] Error 2
  make: *** [Makefile:240: __sub-make] Error 2
  klp-build: error: module build failed

I'm guessing that this happens because of the huge dependency line in
klp-tmp/out/Kbuild for livepatch-y, it includes over 2000 object files
(that I'm pretty sure didn't change :)

I can set this up on a live machine next week if you want to investigate
further.

--
Joe