[RFC] New threadnum command for breakpoints

Frederic RISS
2006-07-28T13:44:26Z

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Hello,

I recently got really frustrated that I couldn't set thread-specific
breakpoints when using the "*<addr>" linespec location. The reason for
this has been discussed already, but I can't seem to find the thread in
the archives. Basically, the "*<addr>" notation treats <addr> as an
expression and the expression parser emits a parse error if you add
'thread xxx' to the line.

This works for breakpoint conditions because "if" is special-cased in
the expression parsers to stop the parsing. At least for C(++), there
can't be any expression typed in GDB that would contain the "if"
reserved keyword, so handling it as a stop condition in the expression
parser is OK. That can't be done for "thread" because it's a valid
language identifier.

The attached patch doesn't try to solve the parsing issue, but it simply
adds a 'threadnum' command that one can use to (un)set the thread of a
particular breakpoint. I'm not sure about the command name, because it
will conflict with the thread command. Suggestions appreciated. I also
wonder if new CLI commands should be added only in the 'cli' subdir?

Of course, the patch is missing a doco part and maybe testsuite
coverage, but I thought I'd first ask if there's interest for this or if
I missed an existing way to do it (seems quite surprising that this
doesn't already exist).
Maybe the alternate approach of adding a $thread variable to use in bp
conditions ( http://www.sourceware.org/ml/gdb/2006-02/msg00017.html )
should be implemented instead ?

Fred.

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2006-07-28 Frederic Riss <frederic.riss@st.com>

* breakpoint.c (threadnum_command): New function.
(_initialize_breakpoint): Register new threadnum command.

Index: breakpoint.c
===================================================================
RCS file: /cvs/src/src/gdb/breakpoint.c,v
retrieving revision 1.227
diff -u -p -r1.227 breakpoint.c
--- breakpoint.c 2 Jun 2006 03:43:18 -0000 1.227
+++ breakpoint.c 27 Jul 2006 20:49:28 -0000
@@ -592,6 +592,43 @@ condition_command (char *arg, int from_t
error (_("No breakpoint number %d."), bnum);
}

+/* threadnum N TID -- set thread of breakpoint N to TID. */
+
+static void
+threadnum_command (char *arg, int from_tty)
+{
+ struct breakpoint *b;
+ char *p;
+ int bnum, threadnum;
+
+ if (arg == 0)
+ error_no_arg (_("breakpoint number"));
+
+ p = arg;
+ bnum = get_number (&p);
+ if (bnum == 0)
+ error (_("Bad breakpoint argument: '%s'"), arg);
+
+ arg = p;
+ threadnum = get_number (&p);
+ if (threadnum == 0)
+ error (_("Bad thread id argument: '%s'"), arg);
+
+ if (threadnum != -1 && !valid_thread_id (threadnum))
+ error (_("Unknown thread %d."), threadnum);
+
+ ALL_BREAKPOINTS (b)
+ if (b->number == bnum)
+ {
+ b->thread = threadnum;
+ breakpoints_changed ();
+ breakpoint_modify_event (b->number);
+ return;
+ }
+
+ error (_("No breakpoint number %d."), bnum);
+}
+
static void
commands_command (char *arg, int from_tty)
{
@@ -7796,6 +7833,12 @@ Specify breakpoint number N to break onl
Usage is `condition N COND', where N is an integer and COND is an\n\
expression to be evaluated whenever breakpoint N is reached."));

+ add_com ("threadnum", class_breakpoint, threadnum_command, _("\
+Specify breakpoint number N to break only in thread TID.\n\
+Usage is `threadnum N TID', where N is an integer and TID is a\n\
+thread identifier as printed by \"info threads\", or -1 for\n\
+any thread."));
+
c = add_com ("tbreak", class_breakpoint, tbreak_command, _("\
Set a temporary breakpoint.\n\
Like \"break\" except the breakpoint is only temporary,\n\