[binutils-gdb] [gdb/testsuite] Require hw watchpoint in gdb.ada/task_watch.exp

[Tom de Vries <vries@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=149700668dca44a0f8e1b0aab1711901935c5bd8

commit 149700668dca44a0f8e1b0aab1711901935c5bd8
Author: Tom de Vries <tdevries@suse.de>
Date:   Mon Nov 28 18:07:12 2022 +0100

    [gdb/testsuite] Require hw watchpoint in gdb.ada/task_watch.exp
    
    On powerpc64le-linux I run into:
    ...
    (gdb) PASS: gdb.ada/task_watch.exp: info tasks before inserting breakpoint
    watch -location value task 3^M
    Watchpoint 2: -location value^M
    (gdb) PASS: gdb.ada/task_watch.exp: watch -location value task 3
    continue^M
    Continuing.^M
    [Thread 0x7ffff7ccf170 (LWP 65550) exited]^M
    [Thread 0x7ffff7abf170 (LWP 65551) exited]^M
    FAIL: gdb.ada/task_watch.exp: continue to watchpoint (timeout)
    ...
    
    On x86_64-linux (where the test-case passes), a hardware watchpoint is used:
    ...
    (gdb) PASS: gdb.ada/task_watch.exp: info tasks before inserting breakpoint
    watch -location value task 3^M
    Hardware watchpoint 2: -location value^M
    ...
    and after forcing "set can-use-hw-watchpoints 0" we can intermittently
    reproduce the same failure.
    
    In the gdb documentation related to watchpoints in multi-threaded programs, we
    read:
    ...
    Warning: In multi-threaded programs, software watchpoints have only limited
    usefulness.  If GDB creates a software watchpoint, it can only watch the value
    of an expression in a single thread.  If you are confident that the expression
    can only change due to the current thread’s activity (and if you are also
    confident that no other thread can become current), then you can use software
    watchpoints as usual.  However, GDB may not notice when a non-current thread’s
    activity changes the expression.  (Hardware watchpoints, in contrast, watch an
    expression in all threads.)
    ...
    
    Since the ada task construct is mapped onto threads, it seems that the
    same limitation holds for tasks.
    
    Fix this by using skip_hw_watchpoint_tests.
    
    Tested on powerpc64-linux.
    Tested-By: Carl Love <cel@us.ibm.com>

Diff:
---
 gdb/testsuite/gdb.ada/task_watch.exp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/gdb/testsuite/gdb.ada/task_watch.exp b/gdb/testsuite/gdb.ada/task_watch.exp
index b22a6204e90..697074ac164 100644
--- a/gdb/testsuite/gdb.ada/task_watch.exp
+++ b/gdb/testsuite/gdb.ada/task_watch.exp
@@ -19,6 +19,8 @@ load_lib "ada.exp"
 
 if { [skip_ada_tests] } { return -1 }
 
+if { [skip_hw_watchpoint_tests] } { return -1 }
+
 standard_ada_testfile foo
 
 if {[gdb_compile_ada "${srcfile}" "${binfile}" executable {debug}] != ""} {