Re: [testsuite patch] for: [PATCH] [PR corefiles/17808] i386: Fix internal error when prstatus in core file is too big

[Mark Kettenis <mark dot kettenis at xs4all dot nl>]

> Date: Fri, 09 Jan 2015 17:19:14 +0000
> From: Pedro Alves <palves@redhat.com>
> 
> On 01/09/2015 04:59 PM, Mark Kettenis wrote:
> >> Date: Fri, 09 Jan 2015 16:27:12 +0000
> >> From: Pedro Alves <palves@redhat.com>
> >>
> >>> Any other comments?
> >>
> >> Do we need to do the same in other places?  This grep seems to suggest yes:
> >>
> >> $ grep assert * | grep sizeof | grep regset
> >> amd64obsd-tdep.c:  gdb_assert (len >= tdep->sizeof_gregset + I387_SIZEOF_FXSAVE);
> >> amd64-tdep.c:  gdb_assert (len == tdep->sizeof_fpregset);
> >> amd64-tdep.c:  gdb_assert (len == tdep->sizeof_fpregset);
> >> i386obsd-tdep.c:  gdb_assert (len >= tdep->sizeof_gregset + I387_SIZEOF_FSAVE);
> >> i386-tdep.c:  gdb_assert (len == tdep->sizeof_gregset);
> >> i386-tdep.c:  gdb_assert (len == tdep->sizeof_gregset);
> >> i386-tdep.c:  gdb_assert (len == tdep->sizeof_fpregset);
> >> i386-tdep.c:  gdb_assert (len == tdep->sizeof_fpregset);
> >> mips-linux-tdep.c:  gdb_assert (len == sizeof (mips_elf_gregset_t));
> >> mips-linux-tdep.c:  gdb_assert (len == sizeof (mips_elf_gregset_t));
> >> mips-linux-tdep.c:  gdb_assert (len == sizeof (mips_elf_fpregset_t));
> >> mips-linux-tdep.c:  gdb_assert (len == sizeof (mips_elf_fpregset_t));
> >> mips-linux-tdep.c:  gdb_assert (len == sizeof (mips64_elf_gregset_t));
> >> mips-linux-tdep.c:  gdb_assert (len == sizeof (mips64_elf_gregset_t));
> >> mips-linux-tdep.c:  gdb_assert (len == sizeof (mips64_elf_fpregset_t));
> >> mips-linux-tdep.c:  gdb_assert (len == sizeof (mips64_elf_fpregset_t));
> >> mn10300-linux-tdep.c:  gdb_assert (len == sizeof (mn10300_elf_gregset_t));
> >> mn10300-linux-tdep.c:  gdb_assert (len == sizeof (mn10300_elf_fpregset_t));
> >> mn10300-linux-tdep.c:  gdb_assert (len == sizeof (mn10300_elf_gregset_t));
> >>
> >> On 01/08/2015 04:16 PM, Andreas Arnez wrote:
> >>> Note that this behavior deviates from the default policy: In general, if
> >>> some future kernel adds new registers to a register set, then a GDB
> >>> unaware of this extension would read the known subset and just ignore
> >>> the unknown bytes.
> >>
> >> That's a good point.
> >>
> >> get_core_register_section checks the section size already:
> >>
> >> get_core_register_section (struct regcache *regcache,
> >> 			   const struct regset *regset,
> >> 			   const char *name,
> >> 			   int min_size,
> >> 			   int which,
> >> 			   const char *human_name,
> >> 			   int required)
> >> {
> >> ...
> >>   size = bfd_section_size (core_bfd, section);
> >>   if (size < min_size)
> >>     {
> >>       warning (_("Section `%s' in core file too small."), section_name);
> >>       return;
> >>     }
> >> ...
> >>
> >> Should we remove all those asserts, and make it the
> >> job of get_core_register_section to warn if the section
> >> size is bigger than expected?  We may need to pass
> >> the "expected" section size to the callback, in addition
> >> to the "minimum" size though.
> > 
> > The code is designed to allow these sections to grow such that the OS
> > kernel can add more registers without breaking GDB.
> 
> Not sure what you're disagreeing with.  My comment is in that direction
> too (And Andreas' comment I'm quoting).  That is, get_core_register_section
> would warn, but still continue processing the section.
> 
> The current code clearly does not work that way, given the assertions.

It shouldn't warn if the sections is bigger that "expected", because
in some cases the "expected" size is really the minimum supported
size, where later versions of the OS added extra information.  At
least not unconditionally.

I can imagine extending the interface to also specify a maximum size
and interpreting a maximum size of 0 as "no maximum".  Continiung
after printing a warning if the section is larger than the maximum
size probably makes sense.

The asserts should probably be changed into >= whatever happens.