RE: [PATCH 3/3] arc: Add support for Newlib

[Anton Kolesov <Anton.Kolesov@synopsys.com>]

Hi Yao,

> -----Original Message-----
> From: Yao Qi [mailto:qiyaoltc@gmail.com]
> Sent: Tuesday, October 11, 2016 5:14 PM
> To: Anton Kolesov <Anton.Kolesov@synopsys.com>
> Cc: gdb-patches@sourceware.org; Francois Bedard <Francois.Bedard@synopsys.com>
> Subject: Re: [PATCH 3/3] arc: Add support for Newlib
> 
> Anton Kolesov <Anton.Kolesov@synopsys.com> writes:
> 
> Hi Anton,
> 
> > +/* Implement the 'init_osabi' method of struct gdb_osabi_handler.  */
> > +
> > +static void
> > +arc_newlib_init_osabi (struct gdbarch_info info, struct gdbarch *gdbarch)
> > +{
> > +  if (arc_debug)
> > +    debug_printf ("arc-newlib: Initialization.\n");
> > +
> > +  struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
> > +
> > +  /* Offset of original PC in longjmp jump buffer (in registers).  Value of
> PC
> > +     offset can be found in newlib/libc/machine/arc/setjmp.S.  */
> > +  tdep->jb_pc = 18;
> 
> What is jb_pc on arc-linux?  Is it 18 or a different one?  If it is 18
> too, we can use arc_get_longjmp_target for both newlib and linux.  Patch
> #1 is not needed.

Unfortunately, it is different in our uClibc port [1] - jb_pc is 15 there.
uClibc saves r13-r25, fp (r27), sp (r28), blink (r31); newlib on the other
hand saves all registers from r13 through r31. Back in time ARC port of GDB
had an "if" inside the get_longjump_target which was selecting offset based
on OS/ABI, instead of using tdep->jb_pc. But using jb_pc, like in arm-tdep.c,
looks like a better solution architecturally.

[1] http://cgit.uclibc-ng.org/cgi/cgit/uclibc-ng.git/tree/libc/sysdeps/linux/arc/bits/setjmp.h

Anton

> 
> --
> Yao (齐尧)