gdb/testsuite/dap: fix gdb.dap/basic-dap.exp disassembly test for PIE

Prior to this patch, I get:

    >>> {"seq": 17, "type": "request", "command": "disassemble", "arguments": {"memoryReference": "0x115d", "instructionCount": 1}}
    Content-Length: 147

    {"request_seq": 17, "type": "response", "command": "disassemble", "success": false, "message": "Cannot access memory at address 0x115d", "seq": 41}FAIL: gdb.dap/basic-dap.exp: disassemble one instruction success
    FAIL: gdb.dap/basic-dap.exp: instructions in disassemble output

The problem is that the PC to disassemble is taken from the breakpoint
insertion response, which happens before running.  With a PIE
executable, that PC is unrelocated, but the disassembly request happens
after relocation.

I chose to fix this by watching for a breakpoint changed event giving
the new breakpoint address, and recording the address from there.  I
think this is an interesting way to fix it, because it adds a bit of
test coverage, I don't think these events are checked right now.

Other ways to fix it would be:

 - Get the address by doing a breakpoint insertion after the program is
   started, or some other way.
 - Do the disassembly by symbol instead of by address.
 - Do the disassembly before running the program.

Change-Id: I3c396f796ac4c8b22e7dfd2fa1c5467f7a47e84e

1 files changed, 30 insertions, 3 deletions

diff --git a/gdb/testsuite/gdb.dap/basic-dap.exp b/gdb/testsuite/gdb.dap/basic-dap.exp
index 795702a..5303e94 100644
--- a/gdb/testsuite/gdb.dap/basic-dap.exp
+++ b/gdb/testsuite/gdb.dap/basic-dap.exp
@@ -90,9 +90,36 @@ set insn_pc [dict get [lindex $bplist 0] instructionReference]
 dap_check_request_and_response "start inferior" configurationDone
 dap_wait_for_event_and_check "inferior started" thread "body reason" started
 
-dap_wait_for_event_and_check "stopped at function breakpoint" stopped \
-    "body reason" breakpoint \
-    "body hitBreakpointIds" $fn_bpno
+# While waiting for the stopped event, we might receive breakpoint changed
+# events indicating some breakpoint addresses were relocated.  Update INSN_PC
+# if necessary.
+lassign [dap_wait_for_event_and_check "stopped at function breakpoint" stopped \
+	    "body reason" breakpoint \
+	    "body hitBreakpointIds" $fn_bpno] unused objs
+foreach obj $objs {
+    if { [dict get $obj "type"] != "event" } {
+	continue
+    }
+
+    if { [dict get $obj "event"] != "breakpoint" } {
+	continue
+    }
+
+    set body [dict get $obj "body"]
+
+    if { [dict get $body "reason"] != "changed" } {
+	continue
+    }
+
+    set breakpoint [dict get $body "breakpoint"]
+    set breakpoint_id [dict get $breakpoint "id"]
+
+    if { $breakpoint_id != $insn_bpno } {
+	continue
+    }
+
+    set insn_pc [dict get $breakpoint "instructionReference"]
+}
 
 set obj [dap_check_request_and_response "evaluate global in function" \
 	     evaluate {o expression [s global_variable]}]