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Disable Z0 packet on aarch64 on multi-arch debugging

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In multi-arch debugging, if GDB sends Z0 packet, GDBserver should be
able to do several things below:

 - choose the right breakpoint instruction to insert according to the
   information available, such as 'kind' in Z0 packet and address,

 - choose the right breakpoint instruction to check memory writes and
   validate inserted memory breakpoint

 - be aware of different breakpoint instructions in $ARCH_breakpoint_at.

unfortunately GDBserver can't do them now.  Although x86 GDBserver
supports multi-arch, it doesn't need to support them above because
breakpoint instruction on i686 and x86_64 is the same.  However,
breakpoint instructions on aarch64 and arm (arm mode, thumb1, and thumb2)
are different.

I tried to teach aarch64 GDBserver backend to be really
multi-arch-capable in the following ways,

 - linux_low_target return the right breakpoint instruction according to
   the 'kind' in Z0 packet, and insert_memory_breakpoint can do the right
   thing.
 - once breakpoint is inserted, the breakpoint data and length is recorded
   in each breakpoint object, so that validate_breakpoint and
   check_mem_write can get the right breakpoint instruction from each
   breakpoint object, rather than from global variable breakpoint_data.
 - linux_low_target needs another hook function for pc increment after
   hitting a breakpoint.
 - let set_breakpoint_at, which is widely used for tracepoint, use the
   'default' breakpoint instruction.  We can always use aarch64 breakpoint
   instruction since arm doesn't support tracepoint yet.

looks it is not a small piece of work, so I decide to disable Z0 packet
on multi-arch, which means aarch64 GDBserver only supports Z0 packet
if it is started to debug only one process (extended protocol is not
used) and process target description is 64-bit.

gdb/gdbserver:

2015-08-04  Yao Qi  <yao.qi@linaro.org>

	* linux-aarch64-low.c (aarch64_supports_z_point_type): Return
	0 for Z_PACKET_SW_BP if it may be used in multi-arch debugging.
	* server.c (extended_protocol): Remove "static".
	* server.h (extended_protocol): Declare it.
This commit is contained in:
Yao Qi 2015-08-04 14:34:14 +01:00
parent 8a7e4587c4
commit 6085d6f695
4 changed files with 25 additions and 1 deletions
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7
gdb/gdbserver/ChangeLog
View file

@ -1,3 +1,10 @@
2015-08-04 Yao Qi <yao.qi@linaro.org>
* linux-aarch64-low.c (aarch64_supports_z_point_type): Return
0 for Z_PACKET_SW_BP if it may be used in multi-arch debugging.
* server.c (extended_protocol): Remove "static".
* server.h (extended_protocol): Declare it.
2015-08-04 Yao Qi <yao.qi@linaro.org>
* linux-aarch64-low.c (aarch64_get_pc): Get PC register on

16
gdb/gdbserver/linux-aarch64-low.c
View file

@ -364,6 +364,22 @@ aarch64_supports_z_point_type (char z_type)
switch (z_type)
{
case Z_PACKET_SW_BP:
{
if (!extended_protocol && is_64bit_tdesc ())
{
/* Only enable Z0 packet in non-multi-arch debugging. If
extended protocol is used, don't enable Z0 packet because
GDBserver may attach to 32-bit process. */
return 1;
}
else
{
/* Disable Z0 packet so that GDBserver doesn't have to handle
different breakpoint instructions (aarch64, arm, thumb etc)
in multi-arch debugging. */
return 0;
}
}
case Z_PACKET_HW_BP:
case Z_PACKET_WRITE_WP:
case Z_PACKET_READ_WP:

2
gdb/gdbserver/server.c
View file

@ -49,7 +49,7 @@ ptid_t general_thread;
int server_waiting;
static int extended_protocol;
int extended_protocol;
static int response_needed;
static int exit_requested;

1
gdb/gdbserver/server.h
View file

@ -87,6 +87,7 @@ extern int multi_process;
extern int report_fork_events;
extern int report_vfork_events;
extern int non_stop;
extern int extended_protocol;
/* True if the "swbreak+" feature is active. In that case, GDB wants
us to report whether a trap is explained by a software breakpoint