Re: [PATCH] Add debug_function_to_file

[Tom de Vries <Tom_deVries at mentor dot com>]

On 17/02/16 14:42, Richard Biener wrote:
> On Wed, Feb 17, 2016 at 1:41 PM, Tom de Vries <Tom_deVries@mentor.com> wrote:
> > Hi,
> >
> > once in a while I'm in a gdb debug session debugging cc1, and want to print
> > the current function to file.
> >
> > There's a debug function debug_function that prints a function to stderr,
> > and there are methods to redirect output of a command to a file (
> > https://sourceware.org/gdb/onlinedocs/gdb/Logging-Output.html ).
> >
> > And there's a function dump_function_to_file that takes a FILE* parameter,
> > which could be combined with open/close calls in gdb.
> >
> > But I think a short-hand is easier.
> >
> > This patch adds a function debug_function_to_file. It can f.i. be called as:
> > ...
> > (gdb) call debug_function_to_file (cfun.decl, "foo.1.txt", 0)
> > ...
> >
> > Hmm, now I wonder if the order 'cfun.decl, 0, "foo.1.txt"' would make more
> > sense (first two parameters the same as in debug_function).
> >
> > OK for stage1 trunk if bootstrap and reg-test succeeds?
>
> Bonus for making this a helper in gdbhooks.py instead, using
> fopen/fclose and the existing inferior calls.

Using attached demonstrator patch, we can use command 
debug-function-to-file in gdb:
...
(gdb) python import sys; sys.path.append('<path>/gcc'); import gdbhooks
Successfully loaded GDB hooks for GCC
(gdb) b tail_merge_optimize
Breakpoint 1 at 0x11be1cc: file gcc/tree-ssa-tail-merge.c, line 1633.
(gdb) r
Starting program: cc1 -quiet hello.c -O2 -o hello.s
Breakpoint 1, tail_merge_optimize (todo=0) at gcc/tree-ssa-tail-merge.c:1633
1633	  int nr_bbs_removed_total = 0;
(gdb) debug-function-to-file "bla.txt"
$1 = 47180688
$2 = <function_decl 0x7ffff61a22a0 main>
$3 = 0
...

and we find that bla.txt contains the result of dump_function_to_file:
...
$ cat bla.txt
main ()
{
  <bb 2>:
  __builtin_puts (&"hello"[0]);
  return 0;

}
...

I would be nice if we could avoid the ${1,2,3} printouts and value 
history assignments, but I'm not sure how to do that.

And given that we have a command with a variable amount of arguments, we 
should try to handle different number of arguments, say these three 
giving the same result:
- debug-function-to-file "bla.txt"
- debug-function-to-file "bla.txt" cfun->decl
- debug-function-to-file "bla.txt" cfun->decl dump_flags
Or perhaps 0 for flags by default, as in pcfun.

Thanks,
- Tom

Add debug-function-to-file to gdbhooks.py

---
 gcc/gdbhooks.py | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/gcc/gdbhooks.py b/gcc/gdbhooks.py
index 0d5cc97..9c230f9 100644
--- a/gcc/gdbhooks.py
+++ b/gcc/gdbhooks.py
@@ -589,4 +589,22 @@ class BreakOnPass(gdb.Command):
 
 BreakOnPass()
 
+class debug_function_to_file(gdb.Command):
+    """
+    """
+    def __init__(self):
+        gdb.Command.__init__(self, 'debug-function-to-file', gdb.COMMAND_USER)
+
+    def invoke(self, arg, from_tty):
+        gdb.execute("call fopen (%s, \"w\")" % arg)
+        fp = gdb.history (0)
+        gdb.execute("p cfun->decl")
+        fn = gdb.history (0)
+        flags = 0
+        dumpargs = "(tree)%u, (FILE *)%u, %u" % (fn, fp, flags)
+        gdb.execute("call dump_function_to_file (%s)" % dumpargs)
+        gdb.execute("call fclose ((FILE *)%u)" % fp)
+
+debug_function_to_file()
+
 print('Successfully loaded GDB hooks for GCC')