[PATCH v2] gdbserver: Check r_version < 1 for Linux debugger interface
H.J. Lu
hjl.tools@gmail.com
Mon Aug 16 22:08:28 GMT 2021
On Mon, Aug 16, 2021 at 3:02 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Mon, Aug 16, 2021 at 1:30 PM H.J. Lu <hjl.tools@gmail.com> wrote:
> >
> > Update gdbserver to check r_version < 1 instead of r_version != 1 so
> > that r_version can be bumped for a new field in the glibc debugger
> > interface to support multiple namespaces. Since so far, the gdbserver
> > only reads fields defined for r_version == 1, it is compatible with
> > r_version >= 1.
> >
> > All future glibc debugger interface changes will be backward compatible.
> > If there is ever the need for backward incompatible change to the glibc
> > debugger interface, a new DT_XXX element will be provided to access the
> > new incompatible interface.
> >
> > PR gdb/11839
> > * linux-low.cc (linux_process_target::qxfer_libraries_svr4):
> > Check r_version < 1 instead of r_version != 1.
> > ---
> > gdbserver/linux-low.cc | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/gdbserver/linux-low.cc b/gdbserver/linux-low.cc
> > index 5c6191d941c..fc7a995351d 100644
> > --- a/gdbserver/linux-low.cc
> > +++ b/gdbserver/linux-low.cc
> > @@ -6845,7 +6845,7 @@ linux_process_target::qxfer_libraries_svr4 (const char *annex,
> > if (linux_read_memory (priv->r_debug + lmo->r_version_offset,
> > (unsigned char *) &r_version,
> > sizeof (r_version)) != 0
> > - || r_version != 1)
> > + || r_version < 1)
> > {
> > warning ("unexpected r_debug version %d", r_version);
> > }
> > --
> > 2.31.1
> >
>
> Set r_version == 2 breaks GDB due to
>
> static CORE_ADDR
> solib_svr4_r_ldsomap (struct svr4_info *info)
> {
> struct link_map_offsets *lmo = svr4_fetch_link_map_offsets ();
> struct type *ptr_type = builtin_type (target_gdbarch ())->builtin_data_ptr;
> enum bfd_endian byte_order = type_byte_order (ptr_type);
> ULONGEST version = 0;
>
> try
> {
> /* Check version, and return zero if `struct r_debug' doesn't have
> the r_ldsomap member. */
> version
> = read_memory_unsigned_integer (info->debug_base +
> lmo->r_version_offset,
> lmo->r_version_size, byte_order);
> }
> catch (const gdb_exception_error &ex)
> {
> exception_print (gdb_stderr, ex);
> }
>
> if (version < 2 || lmo->r_ldsomap_offset == -1)
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> glibc doesn't have r_ldsomap. But r_ldsomap_offset is set
> unconditionally. Shouldn't it be set only if the target debugger
> interface has it?
>
> return 0;
>
> return read_memory_typed_address (info->debug_base + lmo->r_ldsomap_offset,
> ptr_type);
> }
>
I opened:
https://sourceware.org/bugzilla/show_bug.cgi?id=28236
--
H.J.
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