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gcc/gcc/gdbhooks.py

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# Python hooks for gdb for debugging GCC
# Copyright (C) 2013-2015 Free Software Foundation, Inc.
# Contributed by David Malcolm <dmalcolm@redhat.com>
# This file is part of GCC.
# GCC is free software; you can redistribute it and/or modify it under
# the terms of the GNU General Public License as published by the Free
# Software Foundation; either version 3, or (at your option) any later
# version.
# GCC is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
# FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
# for more details.
# You should have received a copy of the GNU General Public License
# along with GCC; see the file COPYING3. If not see
# <http://www.gnu.org/licenses/>.
"""
Enabling the debugging hooks
----------------------------
gcc/configure (from configure.ac) generates a .gdbinit within the "gcc"
subdirectory of the build directory, and when run by gdb, this imports
gcc/gdbhooks.py from the source directory, injecting useful Python code
into gdb.
You may see a message from gdb of the form:
"path-to-build/gcc/.gdbinit" auto-loading has been declined by your `auto-load safe-path'
as a protection against untrustworthy python scripts. See
http://sourceware.org/gdb/onlinedocs/gdb/Auto_002dloading-safe-path.html
The fix is to mark the paths of the build/gcc directory as trustworthy.
An easy way to do so is by adding the following to your ~/.gdbinit script:
add-auto-load-safe-path /absolute/path/to/build/gcc
for the build directories for your various checkouts of gcc.
If it's working, you should see the message:
Successfully loaded GDB hooks for GCC
as gdb starts up.
During development, I've been manually invoking the code in this way, as a
precanned way of printing a variety of different kinds of value:
gdb \
-ex "break expand_gimple_stmt" \
-ex "run" \
-ex "bt" \
--args \
./cc1 foo.c -O3
Examples of output using the pretty-printers
--------------------------------------------
Pointer values are generally shown in the form:
<type address extra_info>
For example, an opt_pass* might appear as:
(gdb) p pass
$2 = <opt_pass* 0x188b600 "expand"(170)>
The name of the pass is given ("expand"), together with the
static_pass_number.
Note that you can dereference the pointer in the normal way:
(gdb) p *pass
$4 = {type = RTL_PASS, name = 0x120a312 "expand",
[etc, ...snipped...]
and you can suppress pretty-printers using /r (for "raw"):
(gdb) p /r pass
$3 = (opt_pass *) 0x188b600
Basic blocks are shown with their index in parentheses, apart from the
CFG's entry and exit blocks, which are given as "ENTRY" and "EXIT":
(gdb) p bb
$9 = <basic_block 0x7ffff041f1a0 (2)>
(gdb) p cfun->cfg->x_entry_block_ptr
$10 = <basic_block 0x7ffff041f0d0 (ENTRY)>
(gdb) p cfun->cfg->x_exit_block_ptr
$11 = <basic_block 0x7ffff041f138 (EXIT)>
CFG edges are shown with the src and dest blocks given in parentheses:
(gdb) p e
$1 = <edge 0x7ffff043f118 (ENTRY -> 6)>
Tree nodes are printed using Python code that emulates print_node_brief,
running in gdb, rather than in the inferior:
(gdb) p cfun->decl
$1 = <function_decl 0x7ffff0420b00 foo>
For usability, the type is printed first (e.g. "function_decl"), rather
than just "tree".
RTL expressions use a kludge: they are pretty-printed by injecting
calls into print-rtl.c into the inferior:
Value returned is $1 = (note 9 8 10 [bb 3] NOTE_INSN_BASIC_BLOCK)
(gdb) p $1
$2 = (note 9 8 10 [bb 3] NOTE_INSN_BASIC_BLOCK)
(gdb) p /r $1
$3 = (rtx_def *) 0x7ffff043e140
This won't work for coredumps, and probably in other circumstances, but
it's a quick way of getting lots of debuggability quickly.
Callgraph nodes are printed with the name of the function decl, if
available:
(gdb) frame 5
#5 0x00000000006c288a in expand_function (node=<cgraph_node* 0x7ffff0312720 "foo">) at ../../src/gcc/cgraphunit.c:1594
1594 execute_pass_list (g->get_passes ()->all_passes);
(gdb) p node
$1 = <cgraph_node* 0x7ffff0312720 "foo">
vec<> pointers are printed as the address followed by the elements in
braces. Here's a length 2 vec:
(gdb) p bb->preds
$18 = 0x7ffff0428b68 = {<edge 0x7ffff044d380 (3 -> 5)>, <edge 0x7ffff044d3b8 (4 -> 5)>}
and here's a length 1 vec:
(gdb) p bb->succs
$19 = 0x7ffff0428bb8 = {<edge 0x7ffff044d3f0 (5 -> EXIT)>}
You cannot yet use array notation [] to access the elements within the
vector: attempting to do so instead gives you the vec itself (for vec[0]),
or a (probably) invalid cast to vec<> for the memory after the vec (for
vec[1] onwards).
Instead (for now) you must access m_vecdata:
(gdb) p bb->preds->m_vecdata[0]
$20 = <edge 0x7ffff044d380 (3 -> 5)>
(gdb) p bb->preds->m_vecdata[1]
$21 = <edge 0x7ffff044d3b8 (4 -> 5)>
"""
import os.path
import re
import gdb
import gdb.printing
import gdb.types
# Convert "enum tree_code" (tree.def and tree.h) to a dict:
tree_code_dict = gdb.types.make_enum_dict(gdb.lookup_type('enum tree_code'))
# ...and look up specific values for use later:
IDENTIFIER_NODE = tree_code_dict['IDENTIFIER_NODE']
TYPE_DECL = tree_code_dict['TYPE_DECL']
# Similarly for "enum tree_code_class" (tree.h):
tree_code_class_dict = gdb.types.make_enum_dict(gdb.lookup_type('enum tree_code_class'))
tcc_type = tree_code_class_dict['tcc_type']
tcc_declaration = tree_code_class_dict['tcc_declaration']
class Tree:
"""
Wrapper around a gdb.Value for a tree, with various methods
corresponding to macros in gcc/tree.h
"""
def __init__(self, gdbval):
self.gdbval = gdbval
def is_nonnull(self):
return long(self.gdbval)
def TREE_CODE(self):
"""
Get gdb.Value corresponding to TREE_CODE (self)
as per:
#define TREE_CODE(NODE) ((enum tree_code) (NODE)->base.code)
"""
return self.gdbval['base']['code']
def DECL_NAME(self):
"""
Get Tree instance corresponding to DECL_NAME (self)
"""
return Tree(self.gdbval['decl_minimal']['name'])
def TYPE_NAME(self):
"""
Get Tree instance corresponding to result of TYPE_NAME (self)
"""
return Tree(self.gdbval['type_common']['name'])
def IDENTIFIER_POINTER(self):
"""
Get str correspoinding to result of IDENTIFIER_NODE (self)
"""
return self.gdbval['identifier']['id']['str'].string()
class TreePrinter:
"Prints a tree"
def __init__ (self, gdbval):
self.gdbval = gdbval
self.node = Tree(gdbval)
def to_string (self):
# like gcc/print-tree.c:print_node_brief
# #define TREE_CODE(NODE) ((enum tree_code) (NODE)->base.code)
# tree_code_name[(int) TREE_CODE (node)])
if long(self.gdbval) == 0:
return '<tree 0x0>'
val_TREE_CODE = self.node.TREE_CODE()
# extern const enum tree_code_class tree_code_type[];
# #define TREE_CODE_CLASS(CODE) tree_code_type[(int) (CODE)]
val_tree_code_type = gdb.parse_and_eval('tree_code_type')
val_tclass = val_tree_code_type[val_TREE_CODE]
val_tree_code_name = gdb.parse_and_eval('tree_code_name')
val_code_name = val_tree_code_name[long(val_TREE_CODE)]
#print val_code_name.string()
result = '<%s 0x%x' % (val_code_name.string(), long(self.gdbval))
if long(val_tclass) == tcc_declaration:
tree_DECL_NAME = self.node.DECL_NAME()
if tree_DECL_NAME.is_nonnull():
result += ' %s' % tree_DECL_NAME.IDENTIFIER_POINTER()
else:
pass # TODO: labels etc
elif long(val_tclass) == tcc_type:
tree_TYPE_NAME = Tree(self.gdbval['type_common']['name'])
if tree_TYPE_NAME.is_nonnull():
if tree_TYPE_NAME.TREE_CODE() == IDENTIFIER_NODE:
result += ' %s' % tree_TYPE_NAME.IDENTIFIER_POINTER()
elif tree_TYPE_NAME.TREE_CODE() == TYPE_DECL:
if tree_TYPE_NAME.DECL_NAME().is_nonnull():
result += ' %s' % tree_TYPE_NAME.DECL_NAME().IDENTIFIER_POINTER()
if self.node.TREE_CODE() == IDENTIFIER_NODE:
result += ' %s' % self.node.IDENTIFIER_POINTER()
# etc
result += '>'
return result
######################################################################
# Callgraph pretty-printers
######################################################################
class CGraphNodePrinter:
def __init__(self, gdbval):
self.gdbval = gdbval
def to_string (self):
result = '<cgraph_node* 0x%x' % long(self.gdbval)
if long(self.gdbval):
# symtab_node::name calls lang_hooks.decl_printable_name
# default implementation (lhd_decl_printable_name) is:
# return IDENTIFIER_POINTER (DECL_NAME (decl));
tree_decl = Tree(self.gdbval['decl'])
result += ' "%s"' % tree_decl.DECL_NAME().IDENTIFIER_POINTER()
result += '>'
return result
######################################################################
# Dwarf DIE pretty-printers
######################################################################
class DWDieRefPrinter:
def __init__(self, gdbval):
self.gdbval = gdbval
def to_string (self):
if long(self.gdbval) == 0:
return '<dw_die_ref 0x0>'
result = '<dw_die_ref 0x%x' % long(self.gdbval)
result += ' %s' % self.gdbval['die_tag']
if long(self.gdbval['die_parent']) != 0:
result += ' <parent=0x%x %s>' % (long(self.gdbval['die_parent']),
self.gdbval['die_parent']['die_tag'])
result += '>'
return result
######################################################################
class GimplePrinter:
def __init__(self, gdbval):
self.gdbval = gdbval
def to_string (self):
if long(self.gdbval) == 0:
return '<gimple 0x0>'
val_gimple_code = self.gdbval['code']
val_gimple_code_name = gdb.parse_and_eval('gimple_code_name')
val_code_name = val_gimple_code_name[long(val_gimple_code)]
result = '<%s 0x%x' % (val_code_name.string(),
long(self.gdbval))
result += '>'
return result
######################################################################
# CFG pretty-printers
######################################################################
def bb_index_to_str(index):
if index == 0:
return 'ENTRY'
elif index == 1:
return 'EXIT'
else:
return '%i' % index
class BasicBlockPrinter:
def __init__(self, gdbval):
self.gdbval = gdbval
def to_string (self):
result = '<basic_block 0x%x' % long(self.gdbval)
if long(self.gdbval):
result += ' (%s)' % bb_index_to_str(long(self.gdbval['index']))
result += '>'
return result
class CfgEdgePrinter:
def __init__(self, gdbval):
self.gdbval = gdbval
def to_string (self):
result = '<edge 0x%x' % long(self.gdbval)
if long(self.gdbval):
src = bb_index_to_str(long(self.gdbval['src']['index']))
dest = bb_index_to_str(long(self.gdbval['dest']['index']))
result += ' (%s -> %s)' % (src, dest)
result += '>'
return result
######################################################################
class Rtx:
def __init__(self, gdbval):
self.gdbval = gdbval
def GET_CODE(self):
return self.gdbval['code']
def GET_RTX_LENGTH(code):
val_rtx_length = gdb.parse_and_eval('rtx_length')
return long(val_rtx_length[code])
def GET_RTX_NAME(code):
val_rtx_name = gdb.parse_and_eval('rtx_name')
return val_rtx_name[code].string()
def GET_RTX_FORMAT(code):
val_rtx_format = gdb.parse_and_eval('rtx_format')
return val_rtx_format[code].string()
class RtxPrinter:
def __init__(self, gdbval):
self.gdbval = gdbval
self.rtx = Rtx(gdbval)
def to_string (self):
"""
For now, a cheap kludge: invoke the inferior's print
function to get a string to use the user, and return an empty
string for gdb
"""
# We use print_inline_rtx to avoid a trailing newline
gdb.execute('call print_inline_rtx (stderr, (const_rtx) %s, 0)'
% long(self.gdbval))
return ''
# or by hand; based on gcc/print-rtl.c:print_rtx
result = ('<rtx_def 0x%x'
% (long(self.gdbval)))
code = self.rtx.GET_CODE()
result += ' (%s' % GET_RTX_NAME(code)
format_ = GET_RTX_FORMAT(code)
for i in range(GET_RTX_LENGTH(code)):
print format_[i]
result += ')>'
return result
######################################################################
class PassPrinter:
def __init__(self, gdbval):
self.gdbval = gdbval
def to_string (self):
result = '<opt_pass* 0x%x' % long(self.gdbval)
if long(self.gdbval):
result += (' "%s"(%i)'
% (self.gdbval['name'].string(),
long(self.gdbval['static_pass_number'])))
result += '>'
return result
######################################################################
class VecPrinter:
# -ex "up" -ex "p bb->preds"
def __init__(self, gdbval):
self.gdbval = gdbval
def display_hint (self):
return 'array'
def to_string (self):
# A trivial implementation; prettyprinting the contents is done
# by gdb calling the "children" method below.
return '0x%x' % long(self.gdbval)
def children (self):
if long(self.gdbval) == 0:
return
m_vecpfx = self.gdbval['m_vecpfx']
m_num = m_vecpfx['m_num']
m_vecdata = self.gdbval['m_vecdata']
for i in range(m_num):
yield ('[%d]' % i, m_vecdata[i])
######################################################################
# TODO:
# * hashtab
# * location_t
class GdbSubprinter(gdb.printing.SubPrettyPrinter):
def __init__(self, name, class_):
super(GdbSubprinter, self).__init__(name)
self.class_ = class_
def handles_type(self, str_type):
raise NotImplementedError
class GdbSubprinterTypeList(GdbSubprinter):
"""
A GdbSubprinter that handles a specific set of types
"""
def __init__(self, str_types, name, class_):
super(GdbSubprinterTypeList, self).__init__(name, class_)
self.str_types = frozenset(str_types)
def handles_type(self, str_type):
return str_type in self.str_types
class GdbSubprinterRegex(GdbSubprinter):
"""
A GdbSubprinter that handles types that match a regex
"""
def __init__(self, regex, name, class_):
super(GdbSubprinterRegex, self).__init__(name, class_)
self.regex = re.compile(regex)
def handles_type(self, str_type):
return self.regex.match(str_type)
class GdbPrettyPrinters(gdb.printing.PrettyPrinter):
def __init__(self, name):
super(GdbPrettyPrinters, self).__init__(name, [])
def add_printer_for_types(self, name, class_, types):
self.subprinters.append(GdbSubprinterTypeList(name, class_, types))
def add_printer_for_regex(self, name, class_, regex):
self.subprinters.append(GdbSubprinterRegex(name, class_, regex))
def __call__(self, gdbval):
type_ = gdbval.type.unqualified()
str_type = str(type_)
for printer in self.subprinters:
if printer.enabled and printer.handles_type(str_type):
return printer.class_(gdbval)
# Couldn't find a pretty printer (or it was disabled):
return None
def build_pretty_printer():
pp = GdbPrettyPrinters('gcc')
pp.add_printer_for_types(['tree'],
'tree', TreePrinter)
pp.add_printer_for_types(['cgraph_node *'],
'cgraph_node', CGraphNodePrinter)
pp.add_printer_for_types(['dw_die_ref'],
'dw_die_ref', DWDieRefPrinter)
pp.add_printer_for_types(['gimple', 'gimple_statement_base *',
# Keep this in the same order as gimple.def:
'gimple_cond', 'const_gimple_cond',
'gimple_statement_cond *',
'gimple_debug', 'const_gimple_debug',
'gimple_statement_debug *',
'gimple_label', 'const_gimple_label',
'gimple_statement_label *',
'gimple_switch', 'const_gimple_switch',
'gimple_statement_switch *',
'gimple_assign', 'const_gimple_assign',
'gimple_statement_assign *',
'gimple_bind', 'const_gimple_bind',
'gimple_statement_bind *',
'gimple_phi', 'const_gimple_phi',
'gimple_statement_phi *'],
'gimple',
GimplePrinter)
pp.add_printer_for_types(['basic_block', 'basic_block_def *'],
'basic_block',
BasicBlockPrinter)
pp.add_printer_for_types(['edge', 'edge_def *'],
'edge',
CfgEdgePrinter)
pp.add_printer_for_types(['rtx_def *'], 'rtx_def', RtxPrinter)
pp.add_printer_for_types(['opt_pass *'], 'opt_pass', PassPrinter)
pp.add_printer_for_regex(r'vec<(\S+), (\S+), (\S+)> \*',
'vec',
VecPrinter)
return pp
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))
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')
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