new syscall stub support for ia64 libc

[David Mosberger]

>>>>> On Mon, 8 Dec 2003 17:08:44 +0100, Jakub Jelinek <jakub@redhat.com> said:

  Jakub> The current IA-64 AT_SYSINFO_EHDR virtual DSO seems to be
  Jakub> unfortunately binary incompatible with older GCCs, which is
  Jakub> IMHO a bad thing.  When kernel provides AT_SYSINFO_EHDR but
  Jakub> userland doesn't grok it yet, things should work the old way.
  Jakub> I think simply swapping the 2 PT_LOAD segments in virtual DSO
  Jakub> would help, ie. put PF_E segment before PF_R.
  Jakub> AT_SYSINFO_EHDR would point to the Elf64_Ehdr (followed by
  Jakub> Elf64_Phdrs) in the PF_R, ie. 0xa000000000020000.

One possitiblity would be for glibc NOT to register the
AT_SYSINFO_EHDR on ia64 for now (i.e., dl_iterate_phdr() wouldn't find
the kernel DSO).  libunwind will then fall back on using the
getunwind() system call.  Not pretty, but it would be backwards compatible.

Of course, longer term, we'd want to get rid of this workaround.  The
question is whether there could be a quick and reliable test to
discover whether the unwinder can handle .unwabi.  Unfortunately this
is complicatd by the fact that we may be dealing with multiple
unwinders (statically linked in and one loaded dynamically via
libgcc_s).

	--david