Re: PING: PATCH: PR backtrace/14646: [x32] backtrace doesn't work

H.J. Lu
2012-10-03T15:59:35Z

On Wed, Oct 3, 2012 at 8:43 AM, Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
>> Date: Wed, 3 Oct 2012 08:26:34 -0700
>> From: "H.J. Lu" <hjl.tools@gmail.com>
>>
>> On Sun, Sep 30, 2012 at 2:40 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> > Hi,
>> >
>> > amd64_x32_init_abi has
>> >
>> > tdep->sp_regnum_from_eax = AMD64_RSP_REGNUM;
>> > tdep->pc_regnum_from_eax = AMD64_RIP_REGNUM;
>> >
>> > But unwind frame info is based on the real RSP/RIP
>> > registers. Pseudo sp/pc registers don't work with
>> > frame related codes:
>> >
>> > [hjl@gnu-tools-1 gdb]$ egrep "pc_regnum|sp_regnum" *fram*.c
>> > dwarf2-frame.c: if (regnum == gdbarch_pc_regnum (gdbarch))
>> > dwarf2-frame.c: else if (regnum == gdbarch_sp_regnum (gdbarch))
>> > dwarf2-frame.c: == gdbarch_sp_regnum (gdbarch)))
>> > dwarf2-frame-tailcall.c: if (regnum == gdbarch_pc_regnum
>> > (this_gdbarch))
>> > dwarf2-frame-tailcall.c: else if (cache->prev_sp_p && regnum ==
>> > gdbarch_sp_regnum (this_gdbarch))
>> > dwarf2-frame-tailcall.c: int sp_regnum;
>> > dwarf2-frame-tailcall.c: sp_regnum = gdbarch_sp_regnum
>> > (prev_gdbarch);
>> > dwarf2-frame-tailcall.c: if (sp_regnum == -1)
>> > dwarf2-frame-tailcall.c: prev_sp = frame_unwind_register_unsigned
>> > (this_frame, sp_regnum);
>> > frame.c: && gdbarch_pc_regnum (gdbarch) >= 0
>> > frame.c: gdbarch_pc_regnum (gdbarch),
>> > frame.c: gdbarch_pc_regnum (gdbarch),
>> > frame.c: the gdbarch_sp_regnum register is meaningful. */
>> > frame.c: if (gdbarch_sp_regnum (gdbarch) >= 0)
>> > frame.c: gdbarch_sp_regnum (gdbarch));
>> > [hjl@gnu-tools-1 gdb]$
>> >
>> > It is nice to print
>> >
>> > (gdb) p $sp
>> > $1 = (void *) 0xffffd028
>> >
>> > instead of
>> >
>> > (gdb) p $sp
>> > $1 = 4294955048
>> >
>> > But it breaks frame unwind. This patch removes pseudo sp/pc regnum from
>> > x32. "p $sp" and "p $pc" will print 64bit integers. But "p $esp" and
>> > "p $esp" work fine. OK for trunk and 4.5 branch?
>> >
>> > Thanks.
>> >
>> >
>> > H.J.
>> > ---
>> > 2012-09-30 H.J. Lu <hongjiu.lu@intel.com>
>> >
>> > PR backtrace/14646
>> > PR gdb/14647
>> > * i386-tdep.h (gdbarch_tdep): Remove sp_regnum_from_eax and
>> > pc_regnum_from_eax.
>> > * i386-tdep.c (i386_gdbarch_init): Don't use sp_regnum_from_eax
>> > nor pc_regnum_from_eax.
>> > * amd64-tdep.c (amd64_x32_init_abi): Don't set sp_regnum_from_eax
>> > nor pc_regnum_from_eax.
>> >
>
> There's got to be a better way to handle that. Did you look into
> using dwarf2_frame_set_init_reg() to establish mappings to the "raw"
> rip and rsp registers?

It doesn't work for x32 since gdbarch_sp_regnum and
gdbarch_pc_regnum are used like:

if (get_frame_func_if_available (this_frame, &entry_pc))
{
/* Decode the insns in the FDE up to the entry PC. */
instr = execute_cfa_program (fde, fde->instructions, fde->end, gdbarch,
entry_pc, fs);

if (fs->regs.cfa_how == CFA_REG_OFFSET
&& (gdbarch_dwarf2_reg_to_regnum (gdbarch, fs->regs.cfa_reg)
== gdbarch_sp_regnum (gdbarch)))
{
entry_cfa_sp_offset = fs->regs.cfa_offset;
entry_cfa_sp_offset_p = 1;
}
}

gdbarch_sp_regnum will return the wrong register number. If there are
gdbarch_frame_sp_regnum and gdbarch_frame_pc_regnum, which
default to gdbarch_sp_regnum and gdbarch_pc_regnum, respectively,
and use them everywhere, except for "p $pc/$sp", x32 can set up proper
gdbarch_frame_sp_regnum and gdbarch_frame_pc_regnum.

--
H.J.