On Tue, Jul 29, 2014 at 04:44:29PM -0400, David Malcolm wrote:
> A complaint I heard at Cauldron with the C++ification of GCC passes is
> that it's become much more difficult to set breakpoints on the execute
> hooks of a pass, now that the passes are classes within anonymous
> namespaces.
Well, its a big annoyance of anonymous namespaces in general.
> When this was first done, the execute methods were trivial
> implementations that called into the existing named functions, which are
> still easy to put a breakpoint on by name (assuming you know the name of
> the function), but some of these have now been converted so that the
> "execute" method is the body of the pass.
The same holds for the gate method, but those are probably less
important in general.
> I did some experimentation, on this box with
> gdb-7.6.50.20130731-19.fc20.x86_64 and gcc trunk r212913 (the latter
> from a week ago).
I don't think anonymous namespaces ever worked well with gdb, and afaik
it hasn't been fixed.
> Thoughts?
ugh, why can somebody just fix gdb is my first reaction, but if its
useful maybe its worth hacks.
Trev
> Dave
>
> gcc/
> * gdbhooks.py (find_gcc_source_dir): New helper function.
> (class PassNames): New class, locating and parsing passes.def.
> (class BreakOnPass): New command "break-on-pass".
>
> diff --git a/gcc/gdbhooks.py b/gcc/gdbhooks.py
> index 85608dc..aeb9199 100644
> --- a/gcc/gdbhooks.py
> +++ b/gcc/gdbhooks.py
> @@ -130,6 +130,7 @@ Instead (for now) you must access m_vecdata:
> (gdb) p bb->preds->m_vecdata[1]
> $21 = <edge 0x7ffff044d3b8 (4 -> 5)>
> """
> +import os.path
> import re
>
> import gdb
> @@ -476,4 +477,71 @@ gdb.printing.register_pretty_printer(
> gdb.current_objfile(),
> build_pretty_printer())
>
> +def find_gcc_source_dir():
> + # Use location of global "g" to locate the source tree
> + sym_g = gdb.lookup_global_symbol('g')
> + path = sym_g.symtab.filename # e.g. '../../src/gcc/context.h'
> + srcdir = os.path.split(path)[0] # e.g. '../../src/gcc'
> + return srcdir
> +
> +class PassNames:
> + """Parse passes.def, gathering a list of pass class names"""
> + def __init__(self):
> + srcdir = find_gcc_source_dir()
> + self.names = []
> + with open(os.path.join(srcdir, 'passes.def')) as f:
> + for line in f:
> + m = re.match('\s*NEXT_PASS \((.+)\);', line)
> + if m:
> + self.names.append(m.group(1))
> +PassNames()
> +
> +class BreakOnPass(gdb.Command):
> + """
> + A custom command for putting breakpoints on the execute hook of passes.
> + This is largely a workaround for issues with tab-completion in gdb when
> + setting breakpoints on methods on classes within anonymous namespaces.
> +
> + Example of use: putting a breakpoint on "final"
> + (gdb) break-on-pass
> + Press <TAB>; it autocompletes to "pass_":
> + (gdb) break-on-pass pass_
> + Press <TAB>:
> + Display all 219 possibilities? (y or n)
> + Press "n"; then type "f":
> + (gdb) break-on-pass pass_f
> + Press <TAB> to autocomplete to pass classnames beginning with "pass_f":
> + pass_fast_rtl_dce pass_fold_builtins
> + pass_feedback_split_functions pass_forwprop
> + pass_final pass_fre
> + pass_fixup_cfg pass_free_cfg
> + Type "in<TAB>" to complete to "pass_final":
> + (gdb) break-on-pass pass_final
> + ...and hit <RETURN>:
> + Breakpoint 6 at 0x8396ba: file ../../src/gcc/final.c, line 4526.
> + ...and we have a breakpoint set; continue execution:
> + (gdb) cont
> + Continuing.
> + Breakpoint 6, (anonymous namespace)::pass_final::execute
> (this=0x17fb990) at ../../src/gcc/final.c:4526
> + 4526 virtual unsigned int execute (function *) { return
> rest_of_handle_final (); }
> + """
> + def __init__(self):
> + gdb.Command.__init__(self, 'break-on-pass', gdb.COMMAND_BREAKPOINTS)
> + self.pass_names = None
> +
> + def complete(self, text, word):
> + # Lazily load pass names:
> + if not self.pass_names:
> + self.pass_names = PassNames()
> +
> + return [name
> + for name in sorted(self.pass_names.names)
> + if name.startswith(text)]
> +
> + def invoke(self, arg, from_tty):
> + sym = '(anonymous namespace)::%s::execute' % arg
> + breakpoint = gdb.Breakpoint(sym)
> +
> +BreakOnPass()
> +
> print('Successfully loaded GDB hooks for GCC')
