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

H.J. Lu
2012-10-08T20:38:29Z

On Mon, Oct 8, 2012 at 1:22 PM, Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
>> Date: Mon, 8 Oct 2012 13:04:03 -0700
>> From: "H.J. Lu" <hjl.tools@gmail.com>
>>
>> On Mon, Oct 8, 2012 at 12:48 PM, Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
>> >> Date: Thu, 4 Oct 2012 06:57:22 -0700
>> >> From: "H.J. Lu" <hjl.tools@gmail.com>
>> >>
>> >> On Wed, Oct 3, 2012 at 11:57 PM, Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
>> >> >
>> >> > Perhaps the user-regs.c mechanism can be used to establish eip -> pc
>> >> > and esp -> sp mappings?
>> >>
>> >> It doesn't help as long as gdbarch_pc_regnum/gdbarch_sp_regnum
>> >> are used for both frame pc/sp value and unwind pc/sp value. For x32,
>> >> we want eip/esp for frame pc/sp value and rip/rsp for unwind pc/sp
>> >> value.
>> >
>> > That probably means we need to set gdbarch_pc_regnum (and
>> > gdbarch_sp_regnum) to -1 for x32.
>>
>> We can't set gdbarch_pc_regnum/gdbarch_sp_regnum to -1:
>>
>>
>> GNU gdb (GDB) 7.5.50.20121008-cvs
>> Copyright (C) 2012 Free Software Foundation, Inc.
>> License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
>> This is free software: you are free to change and redistribute it.
>> There is NO WARRANTY, to the extent permitted by law. Type "show copying"
>> and "show warranty" for details.
>> This GDB was configured as "x86_64-unknown-linux-gnu".
>> For bug reporting instructions, please see:
>> <http://www.gnu.org/software/gdb/bugs/>...
>> Reading symbols from
>> /export/build/gnu/glibc-x32/build-x86_64-linux/elf/sln...done.
>> (gdb) b main
>> Breakpoint 1 at 0x400c20: file sln.c, line 50.
>> (gdb) r
>> Starting program: /export/build/gnu/glibc-x32/build-x86_64-linux/elf/sln
>> /export/gnu/import/git/gdb/gdb/regcache.c:1062: internal-error:
>> regcache_read_pc: Unable to find PC
>> A problem internal to GDB has been detected,
>> further debugging may prove unreliable.
>> Quit this debugging session? (y or n)
>
> Well, obviously you'll need to implement gdbarch_read_pc() for this to
> work. And probably a few more gdbarch methods.

What do we gain by setting gdbarch_pc_regnum/gdbarch_sp_regnum
to -1? PC and SP are RIP and RSP for x32. We need them for
stack unwind. The only unusual part is they are 64-bit although
x32 is a 32-bit environment. How about this change?

diff --git a/gdb/features/i386/x32-core.xml b/gdb/features/i386/x32-core.xml
index 1e41417..392ce24 100644
--- a/gdb/features/i386/x32-core.xml
+++ b/gdb/features/i386/x32-core.xml
@@ -34,7 +34,7 @@
<reg name="rsi" bitsize="64" type="int64"/>
<reg name="rdi" bitsize="64" type="int64"/>
<reg name="rbp" bitsize="64" type="int64"/>
- <reg name="rsp" bitsize="64" type="int64"/>
+ <reg name="rsp" bitsize="64" type="data_ptr"/>
<reg name="r8" bitsize="64" type="int64"/>
<reg name="r9" bitsize="64" type="int64"/>
<reg name="r10" bitsize="64" type="int64"/>
@@ -44,7 +44,7 @@
<reg name="r14" bitsize="64" type="int64"/>
<reg name="r15" bitsize="64" type="int64"/>

- <reg name="rip" bitsize="64" type="uint64"/>
+ <reg name="rip" bitsize="64" type="code_ptr"/>
<reg name="eflags" bitsize="32" type="i386_eflags"/>
<reg name="cs" bitsize="32" type="int32"/>
<reg name="ss" bitsize="32" type="int32"/>

--
H.J.