Re: [PATCH][gdb] Fix fbsd core matching

[Alan Modra <amodra@gmail.com>]

On Thu, Jun 09, 2022 at 08:59:37AM -0700, John Baldwin wrote:
> On 6/9/22 1:58 AM, Tom de Vries via Gdb-patches wrote:
> > Hi,
> > 
> > With an --enable-targets=all build and target board unix/-m32 I run into a
> > FAIL in test-case gdb.base/corefile.exp:
> > ...
> > (gdb) file outputs/gdb.base/corefile/corefile^M
> > Reading symbols from outputs/gdb.base/corefile/corefile...^M
> > (gdb) core-file outputs/gdb.base/corefile/corefile.core^M
> > warning: core file may not match specified executable file.^M
> > [New LWP 12011]^M
> > Core was generated by `outputs/gdb.base/corefile/co'.^M
> > Program terminated with signal SIGABRT, Aborted.^M
> > (gdb) FAIL: gdb.base/corefile.exp: core-file warning-free
> > ...
> > 
> > The warning is there because of this mismatch between core and exec:
> > ...
> > (gdb) p core_bfd->xvec
> > $3 = (const struct bfd_target *) 0x20112a0 <i386_elf32_fbsd_vec>
> > (gdb) p exec_bfd->xvec
> > $4 = (const struct bfd_target *) 0x2010b00 <i386_elf32_vec>
> > ...
> > 
> > In the exec case, the detected architecture is i386_elf32_vec because this bit
> > of code in elfcode.h:elf_object_p():
> > ...
> >    if (ebd->elf_machine_code != EM_NONE
> >        && i_ehdrp->e_ident[EI_OSABI] != ebd->elf_osabi
> >        && ebd->elf_osabi != ELFOSABI_NONE)
> >      goto got_wrong_format_error;
> > ...
> > prevents i386_elf32_fbsd from matching.
> > 
> > Fix the core matching by copying that code to elfcore.h:elf_core_file_p().
> > 
> > Tested on x86_64-linux.
> > 
> > Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29227
> > 
> > Any comments?

Looks good.

> Looking at elfcore.h, it seems to have not gotten changes made to elfcode.h over
> time and is a bit rotted.  I suspect that all of changes made in commit 0aabe54e6222
> that added these lines in elfcode.h (along with several other changes) need to
> be applied to this function in elfcore.h, not just adding these lines.

Yes, the commit 0aabe54e6222 changes likely should go in too.  I'm a
little wary of adding all the sanity checks to elf_core_file_p since
that might result in some core files not being recognised at all.  For
example, despite the FIXME I'd guess leaving out the EI_VERSION check
was deliberate.  The following seems reasonable to me.  Please test.

diff --git a/bfd/elfcore.h b/bfd/elfcore.h
index 809f6711aed..59b73bd57de 100644
--- a/bfd/elfcore.h
+++ b/bfd/elfcore.h
@@ -149,37 +149,14 @@ elf_core_file_p (bfd *abfd)
       && (ebd->elf_machine_alt1 == 0
 	  || i_ehdrp->e_machine != ebd->elf_machine_alt1)
       && (ebd->elf_machine_alt2 == 0
-	  || i_ehdrp->e_machine != ebd->elf_machine_alt2))
-    {
-      const bfd_target * const *target_ptr;
-
-      if (ebd->elf_machine_code != EM_NONE)
-	goto wrong;
-
-      /* This is the generic ELF target.  Let it match any ELF target
-	 for which we do not have a specific backend.  */
+	  || i_ehdrp->e_machine != ebd->elf_machine_alt2)
+      && ebd->elf_machine_code != EM_NONE)
+    goto wrong;
 
-      for (target_ptr = bfd_target_vector; *target_ptr != NULL; target_ptr++)
-	{
-	  const struct elf_backend_data *back;
-
-	  if ((*target_ptr)->flavour != bfd_target_elf_flavour)
-	    continue;
-	  back = xvec_get_elf_backend_data (*target_ptr);
-	  if (back->s->arch_size != ARCH_SIZE)
-	    continue;
-	  if (back->elf_machine_code == i_ehdrp->e_machine
-	      || (back->elf_machine_alt1 != 0
-		  && i_ehdrp->e_machine == back->elf_machine_alt1)
-	      || (back->elf_machine_alt2 != 0
-		  && i_ehdrp->e_machine == back->elf_machine_alt2))
-	    {
-	      /* target_ptr is an ELF backend which matches this
-		 object file, so reject the generic ELF target.  */
-	      goto wrong;
-	    }
-	}
-    }
+  if (ebd->elf_machine_code != EM_NONE
+      && i_ehdrp->e_ident[EI_OSABI] != ebd->elf_osabi
+      && ebd->elf_osabi != ELFOSABI_NONE)
+    goto wrong;
 
   /* If there is no program header, or the type is not a core file, then
      we are hosed.  */
@@ -199,6 +176,9 @@ elf_core_file_p (bfd *abfd)
       Elf_Internal_Shdr i_shdr;
       file_ptr where = (file_ptr) i_ehdrp->e_shoff;
 
+      if (i_ehdrp->e_shoff < sizeof (x_ehdr))
+	goto wrong;
+
       /* Seek to the section header table in the file.  */
       if (bfd_seek (abfd, where, SEEK_SET) != 0)
 	goto fail;

> I've cc'd Alan who made that commit above to elfcore.h.  There also seem to be
> some other inconsistencies between the functions in elfcore.h and and elfcode.h
> and perhaps the common functionality in these functions could be refactored
> into a separate function to avoid the code duplication?
> 
> Note that the issue isn't really FreeBSD specific, I just suspect that the FreeBSD
> i386 vec happens to be sorted first in the list for some reason.
> > Thanks,
> > - Tom
> > 
> > [gdb] Fix fbsd core matching
> > 
> > ---
> >   bfd/elfcore.h | 5 +++++
> >   1 file changed, 5 insertions(+)
> > 
> > diff --git a/bfd/elfcore.h b/bfd/elfcore.h
> > index 809f6711aed..4ce81e2e383 100644
> > --- a/bfd/elfcore.h
> > +++ b/bfd/elfcore.h
> > @@ -272,6 +272,11 @@ elf_core_file_p (bfd *abfd)
> >         && ebd->elf_machine_code != EM_NONE)
> >       goto fail;
> > +  if (ebd->elf_machine_code != EM_NONE
> > +      && i_ehdrp->e_ident[EI_OSABI] != ebd->elf_osabi
> > +      && ebd->elf_osabi != ELFOSABI_NONE)
> > +    goto fail;
> > +
> >     /* Let the backend double check the format and override global
> >        information.  We do this before processing the program headers
> >        to allow the correct machine (as opposed to just the default
> 
> 
> -- 
> John Baldwin

-- 
Alan Modra
Australia Development Lab, IBM