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Re: [PATCH] Let gdbserver doesn't tell GDB it support target-side breakpoint conditions and commands if it doesn't support 'Z' packet
- From: Hui Zhu <hui_zhu at mentor dot com>
- To: Pedro Alves <palves at redhat dot com>
- Cc: gdb-patches ml <gdb-patches at sourceware dot org>
- Date: Thu, 28 Nov 2013 17:07:19 +0800
- Subject: Re: [PATCH] Let gdbserver doesn't tell GDB it support target-side breakpoint conditions and commands if it doesn't support 'Z' packet
- Authentication-results: sourceware.org; auth=none
- References: <5265022F dot 8060203 at mentor dot com> <52654A2C dot 9010202 at redhat dot com>
On 10/21/13 23:37, Pedro Alves wrote:
On 10/21/2013 11:30 AM, Hui Zhu wrote:
We found that in powerpc arch board, it cannot pass some dprintf test:
FAIL: gdb.base/dprintf.exp: dprintf info 2 (pattern 6)
FAIL: gdb.mi/mi-dprintf.exp: mi expect stop (unknown output after running)
FAIL: gdb.mi/mi-dprintf.exp: mi 1st dprintf, agent (unknown output after running)
This because the gdbserver will always tell GDB that it support target-side breakpoint conditions and commands. So "set dprintf-style agent" will always got success.
But target-side breakpoint conditions and commands are depend on 'Z' packet because GDB just can post target-side breakpoint conditions and commands with 'Z' packet.
The test will check if "set dprintf-style agent" success or not. Because it will always succes. So GDB change the commands to agent-printf that will make test get fail.
There happens to be a single "the_low_target.insert_point" entry
point in gdbserver for all sorts of Z packets. But Z0, Z1, Z2, etc.,
they're all different packets (software breakpoints, hardware breakpoints,
watchpoints, etc.). A target might well support Z1 but not Z0. Or it
may support Z2/Z3/Z4, but not Z0..Z1 -- that's the case of MIPS gdbserver.
So, having a "the_low_target.insert_point" hook installed does not
actually mean that dprintf will work. (Consider what the patch
would need to do if instead of a single "the_low_target.insert_point"
entry point, we had one for each Zx packet.)
In the general case, gdbserver can't possibly know what packet GDB
will want to send with target conditions or target commands in. GDB
could end up sending either a Z0, or a Z1. The target might support
Z1, but not Z0, leaving gdb to handle memory breakpoints.
The concept of target-side conditions and commands is broader
I think that first, GDB should be taught to handle this scenario
itself. That is, if we try this against gdbserver:
(gdb) set dprintf-style agent
(gdb) set remote Z-packet off
(gdb) dprint main,"foo"
Dprintf 1 at 0x410776: file foo.c, line 10.
GDB should realize that the dprintf won't work, right
at insertion time, but, it currently does not.
According to your comments. I make a new patch for it.
It add a check in remote_insert_breakpoint. If this breakpoint have target breakpoint but it is not handled by "Z" packet, function will return error.
Please help me review it.
Because mi-dprintf.exp and dprintf.exp use "set dprintf-style agent" check if target support target-side breakpoint, they are still got fail after this patch.
If you think this patch's idea is OK, I will make patch for them.
2013-11-28 Hui Zhu <firstname.lastname@example.org>
* remote.c (remote_insert_breakpoint): Add
@@ -8187,6 +8187,14 @@ static int
remote_insert_breakpoint (struct gdbarch *gdbarch,
struct bp_target_info *bp_tgt)
+ int have_target_target_side_commands = 0;
+ /* Check bp_tgt->tcommands in this place because
+ remote_add_target_side_commands will release bp_tgt->tcommands. */
+ if (!VEC_empty (agent_expr_p, bp_tgt->tcommands))
+ have_target_target_side_commands = 1;
/* Try the "Z" s/w breakpoint packet if it is not already disabled.
If it succeeds, then set the support to PACKET_ENABLE. If it
fails, and the user has explicitly requested the Z support then
@@ -8240,6 +8248,13 @@ remote_insert_breakpoint (struct gdbarch
+ if (have_target_target_side_commands)
+ warning (_("\
+Target doesn't support breakpoints that have target side commands."));
+ return -1;
return memory_insert_breakpoint (gdbarch, bp_tgt);