Re: PATCH: Enable x86 XML target descriptions

H.J. Lu
2010-02-22T15:27:40Z

On Mon, Feb 22, 2010 at 7:01 AM, Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
>> Date: Mon, 22 Feb 2010 06:17:29 -0800
>> From: "H.J. Lu" <hjl.tools@gmail.com>
>>
>> >> +/* Get Linux/x86 target description from running target.  */
>> >> +
>> >> +static const struct target_desc *
>> >> +amd64_linux_read_description (struct target_ops *ops)
>> >> +{
>> >> +  if (gdbarch_ptr_bit (target_gdbarch) == 64)
>> >> +    return tdesc_amd64_linux;
>> >> +  else
>> >> +    return tdesc_i386_linux;
>> >> +}
>> >> +
>> >
>> > This made me wonder what happens if you attach to a process without
>> > loading an executable first.  Currently this works, since GDB can
>> > figure out what executable belongs to the the process and load the
>> > executable automatically.  But I fear a chicken & egg problem here:
>> > the gdbarch is derviced from the tdesc, but in order to determine the
>> > tdesc you need a gdbarch.
>>
>> How do you attach to a process without loading an executable first?
>> Gdb has to load something to debug. Do you have a testcase? I will
>> fix it if it doesn't work already.
>
> $ gdb
> ...
> (gdb) attach PID
>
>

It works fine. amd64_linux_read_description is called via

(gdb) att 20026
Attaching to process 20026
Reading symbols from /export/home/hjl/bugs/gdb/xml/p...done.
Detaching after fork from child process 20039.

Breakpoint 3, amd64_linux_read_description (ops=0xa94900)
at /export/gnu/import/git/gdb-avx/gdb/amd64-linux-nat.c:681
681 {
Missing separate debuginfos, use: debuginfo-install
expat-2.0.1-8.fc12.x86_64 glibc-2.11.1-2.2.f12.x86_64
ncurses-libs-5.7-3.20090207.fc12.x86_64 python-2.6.2-2.fc12.x86_64
python-libs-2.6.2-2.fc12.x86_64 zlib-1.2.3-23.fc12.x86_64
(top-gdb) bt
#0 amd64_linux_read_description (ops=0xa94900)
at /export/gnu/import/git/gdb-avx/gdb/amd64-linux-nat.c:681
#1 0x000000000054be91 in target_read_description (
target=<value optimized out>)
at /export/gnu/import/git/gdb-avx/gdb/target.c:2252
#2 0x00000000005c423a in target_find_description ()
at /export/gnu/import/git/gdb-avx/gdb/target-descriptions.c:279
#3 0x000000000051e266 in post_create_inferior (target=0xa74be0, from_tty=1)
at /export/gnu/import/git/gdb-avx/gdb/infcmd.c:402
#4 0x000000000051e36f in attach_command_post_wait (
args=<value optimized out>, from_tty=1, async_exec=0)
at /export/gnu/import/git/gdb-avx/gdb/infcmd.c:2249
#5 0x000000000051e7fd in attach_command (args=0xa77104 "20026", from_tty=1)
at /export/gnu/import/git/gdb-avx/gdb/infcmd.c:2426
#6 0x00000000004559eb in execute_command (p=0xa77108 "6", from_tty=1)
at /export/gnu/import/git/gdb-avx/gdb/top.c:441
#7 0x0000000000535947 in command_handler (command=0xa77100 "")
at /export/gnu/import/git/gdb-avx/gdb/event-top.c:511
#8 0x0000000000536564 in command_line_handler (rl=<value optimized out>)
at /export/gnu/import/git/gdb-avx/gdb/event-top.c:736
#9 0x00000000005fb487 in rl_callback_read_char ()
at /export/gnu/import/git/gdb-avx/readline/callback.c:205
#10 0x0000000000535a79 in rl_callback_read_char_wrapper (
---Type <return> to continue, or q <return> to quit---
client_data=<value optimized out>)
at /export/gnu/import/git/gdb-avx/gdb/event-top.c:178
#11 0x00000000005343a8 in process_event ()
at /export/gnu/import/git/gdb-avx/gdb/event-loop.c:393
#12 0x00000000005354da in gdb_do_one_event (data=<value optimized out>)
at /export/gnu/import/git/gdb-avx/gdb/event-loop.c:458
#13 0x000000000052f75b in catch_errors (func=<value optimized out>,
func_args=<value optimized out>, errstring=<value optimized out>,
mask=<value optimized out>)
at /export/gnu/import/git/gdb-avx/gdb/exceptions.c:510
#14 0x00000000004bf610 in tui_command_loop (data=<value optimized out>)
at /export/gnu/import/git/gdb-avx/gdb/tui/tui-interp.c:154
#15 0x000000000044d489 in captured_command_loop (data=<value optimized out>)
at /export/gnu/import/git/gdb-avx/gdb/main.c:226
#16 0x000000000052f75b in catch_errors (func=<value optimized out>,
func_args=<value optimized out>, errstring=<value optimized out>,
mask=<value optimized out>)
at /export/gnu/import/git/gdb-avx/gdb/exceptions.c:510
#17 0x000000000044cebe in captured_main (data=<value optimized out>)
at /export/gnu/import/git/gdb-avx/gdb/main.c:905
#18 0x000000000052f75b in catch_errors (func=<value optimized out>,
func_args=<value optimized out>, errstring=<value optimized out>,
mask=<value optimized out>)
---Type <return> to continue, or q <return> to quit---
at /export/gnu/import/git/gdb-avx/gdb/exceptions.c:510
#19 0x000000000044c354 in gdb_main (args=0x0)
at /export/gnu/import/git/gdb-avx/gdb/main.c:914
#20 0x000000000044c31e in main (argc=10957472, argv=<value optimized out>)
at /export/gnu/import/git/gdb-avx/gdb/gdb.c:33
(top-gdb)

--
H.J.