296 lines
11 KiB
Python
296 lines
11 KiB
Python
# Copyright 2011-2016 Free Software Foundation, Inc.
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#
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# This is free software: you can redistribute it and/or modify it
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# under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful, but
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# WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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# General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see
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# <http://www.gnu.org/licenses/>.
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# This is a GCC plugin that computes some exception-handling data for
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# gdb. This data can then be summarized and checked by the
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# exsummary.py script.
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# To use:
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# * First, install the GCC Python plugin. See
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# https://fedorahosted.org/gcc-python-plugin/
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# * export PYTHON_PLUGIN=/full/path/to/plugin/directory
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# This should be the directory holding "python.so".
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# * cd build/gdb; make mostlyclean
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# * make CC=.../gcc-with-excheck
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# This will write a number of .py files in the build directory.
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# * python .../exsummary.py
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# This will show the violations.
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import gcc
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import gccutils
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import sys
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# Where our output goes.
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output_file = None
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# Cleanup functions require special treatment, because they take a
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# function argument, but in theory the function must be nothrow.
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cleanup_functions = {
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'make_cleanup': 1,
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'make_cleanup_dtor': 1,
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'make_final_cleanup': 1,
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'make_my_cleanup2': 1,
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'make_my_cleanup': 1
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}
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# Functions which may throw but which we want to ignore.
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ignore_functions = {
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# This one is super special.
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'exceptions_state_mc': 1,
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# gdb generally pretends that internal_error cannot throw, even
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# though it can.
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'internal_error': 1,
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# do_cleanups and friends are supposedly nothrow but we don't want
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# to run afoul of the indirect function call logic.
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'do_cleanups': 1,
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'do_final_cleanups': 1
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}
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# Functions which take a function argument, but which are not
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# interesting, usually because the argument is not called in the
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# current context.
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non_passthrough_functions = {
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'signal': 1,
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'add_internal_function': 1
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}
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# Return True if the type is from Python.
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def type_is_pythonic(t):
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if isinstance(t, gcc.ArrayType):
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t = t.type
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if not isinstance(t, gcc.RecordType):
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return False
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# Hack.
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return str(t).find('struct Py') == 0
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# Examine all the fields of a struct. We don't currently need any
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# sort of recursion, so this is simple for now.
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def examine_struct_fields(initializer):
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global output_file
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for idx2, value2 in initializer.elements:
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if isinstance(idx2, gcc.Declaration):
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if isinstance(value2, gcc.AddrExpr):
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value2 = value2.operand
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if isinstance(value2, gcc.FunctionDecl):
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output_file.write("declare_nothrow(%s)\n"
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% repr(str(value2.name)))
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# Examine all global variables looking for pointers to functions in
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# structures whose types were defined by Python.
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def examine_globals():
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global output_file
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vars = gcc.get_variables()
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for var in vars:
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if not isinstance(var.decl, gcc.VarDecl):
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continue
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output_file.write("################\n")
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output_file.write("# Analysis for %s\n" % var.decl.name)
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if not var.decl.initial:
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continue
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if not type_is_pythonic(var.decl.type):
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continue
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if isinstance(var.decl.type, gcc.ArrayType):
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for idx, value in var.decl.initial.elements:
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examine_struct_fields(value)
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else:
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gccutils.check_isinstance(var.decl.type, gcc.RecordType)
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examine_struct_fields(var.decl.initial)
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# Called at the end of compilation to write out some data derived from
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# globals and to close the output.
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def close_output(*args):
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global output_file
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examine_globals()
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output_file.close()
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# The pass which derives some exception-checking information. We take
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# a two-step approach: first we get a call graph from the compiler.
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# This is emitted by the plugin as Python code. Then, we run a second
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# program that reads all the generated Python and uses it to get a
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# global view of exception routes in gdb.
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class GdbExceptionChecker(gcc.GimplePass):
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def __init__(self, output_file):
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gcc.GimplePass.__init__(self, 'gdb_exception_checker')
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self.output_file = output_file
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def log(self, obj):
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self.output_file.write("# %s\n" % str(obj))
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# Return true if FN is a call to a method on a Python object.
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# We know these cannot throw in the gdb sense.
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def fn_is_python_ignorable(self, fn):
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if not isinstance(fn, gcc.SsaName):
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return False
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stmt = fn.def_stmt
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if not isinstance(stmt, gcc.GimpleAssign):
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return False
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if stmt.exprcode is not gcc.ComponentRef:
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return False
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rhs = stmt.rhs[0]
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if not isinstance(rhs, gcc.ComponentRef):
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return False
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if not isinstance(rhs.field, gcc.FieldDecl):
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return False
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return rhs.field.name == 'tp_dealloc' or rhs.field.name == 'tp_free'
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# Decode a function call and write something to the output.
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# THIS_FUN is the enclosing function that we are processing.
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# FNDECL is the call to process; it might not actually be a DECL
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# node.
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# LOC is the location of the call.
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def handle_one_fndecl(self, this_fun, fndecl, loc):
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callee_name = ''
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if isinstance(fndecl, gcc.AddrExpr):
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fndecl = fndecl.operand
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if isinstance(fndecl, gcc.FunctionDecl):
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# Ordinary call to a named function.
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callee_name = str(fndecl.name)
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self.output_file.write("function_call(%s, %s, %s)\n"
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% (repr(callee_name),
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repr(this_fun.decl.name),
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repr(str(loc))))
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elif self.fn_is_python_ignorable(fndecl):
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# Call to tp_dealloc.
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pass
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elif (isinstance(fndecl, gcc.SsaName)
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and isinstance(fndecl.var, gcc.ParmDecl)):
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# We can ignore an indirect call via a parameter to the
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# current function, because this is handled via the rule
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# for passthrough functions.
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pass
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else:
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# Any other indirect call.
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self.output_file.write("has_indirect_call(%s, %s)\n"
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% (repr(this_fun.decl.name),
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repr(str(loc))))
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return callee_name
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# This does most of the work for examine_one_bb.
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# THIS_FUN is the enclosing function.
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# BB is the basic block to process.
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# Returns True if this block is the header of a TRY_CATCH, False
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# otherwise.
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def examine_one_bb_inner(self, this_fun, bb):
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if not bb.gimple:
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return False
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try_catch = False
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for stmt in bb.gimple:
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loc = stmt.loc
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if not loc:
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loc = this_fun.decl.location
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if not isinstance(stmt, gcc.GimpleCall):
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continue
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callee_name = self.handle_one_fndecl(this_fun, stmt.fn, loc)
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if callee_name == 'exceptions_state_mc_action_iter':
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try_catch = True
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global non_passthrough_functions
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if callee_name in non_passthrough_functions:
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continue
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# We have to specially handle calls where an argument to
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# the call is itself a function, e.g., qsort. In general
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# we model these as "passthrough" -- we assume that in
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# addition to the call the qsort there is also a call to
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# the argument function.
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for arg in stmt.args:
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# We are only interested in arguments which are functions.
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t = arg.type
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if isinstance(t, gcc.PointerType):
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t = t.dereference
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if not isinstance(t, gcc.FunctionType):
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continue
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if isinstance(arg, gcc.AddrExpr):
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arg = arg.operand
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global cleanup_functions
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if callee_name in cleanup_functions:
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if not isinstance(arg, gcc.FunctionDecl):
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gcc.inform(loc, 'cleanup argument not a DECL: %s' % repr(arg))
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else:
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# Cleanups must be nothrow.
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self.output_file.write("declare_cleanup(%s)\n"
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% repr(str(arg.name)))
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else:
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# Assume we have a passthrough function, like
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# qsort or an iterator. We model this by
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# pretending there is an ordinary call at this
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# point.
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self.handle_one_fndecl(this_fun, arg, loc)
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return try_catch
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# Examine all the calls in a basic block and generate output for
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# them.
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# THIS_FUN is the enclosing function.
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# BB is the basic block to examine.
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# BB_WORKLIST is a list of basic blocks to work on; we add the
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# appropriate successor blocks to this.
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# SEEN_BBS is a map whose keys are basic blocks we have already
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# processed. We use this to ensure that we only visit a given
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# block once.
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def examine_one_bb(self, this_fun, bb, bb_worklist, seen_bbs):
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try_catch = self.examine_one_bb_inner(this_fun, bb)
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for edge in bb.succs:
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if edge.dest in seen_bbs:
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continue
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seen_bbs[edge.dest] = 1
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if try_catch:
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# This is bogus, but we magically know the right
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# answer.
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if edge.false_value:
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bb_worklist.append(edge.dest)
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else:
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bb_worklist.append(edge.dest)
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# Iterate over all basic blocks in THIS_FUN.
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def iterate_bbs(self, this_fun):
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# Iteration must be in control-flow order, because if we see a
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# TRY_CATCH construct we need to drop all the contained blocks.
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bb_worklist = [this_fun.cfg.entry]
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seen_bbs = {}
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seen_bbs[this_fun.cfg.entry] = 1
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for bb in bb_worklist:
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self.examine_one_bb(this_fun, bb, bb_worklist, seen_bbs)
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def execute(self, fun):
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if fun and fun.cfg and fun.decl:
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self.output_file.write("################\n")
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self.output_file.write("# Analysis for %s\n" % fun.decl.name)
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self.output_file.write("define_function(%s, %s)\n"
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% (repr(fun.decl.name),
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repr(str(fun.decl.location))))
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global ignore_functions
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if fun.decl.name not in ignore_functions:
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self.iterate_bbs(fun)
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def main(**kwargs):
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global output_file
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output_file = open(gcc.get_dump_base_name() + '.gdb_exc.py', 'w')
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# We used to use attributes here, but there didn't seem to be a
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# big benefit over hard-coding.
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output_file.write('declare_throw("throw_exception")\n')
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output_file.write('declare_throw("throw_verror")\n')
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output_file.write('declare_throw("throw_vfatal")\n')
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output_file.write('declare_throw("throw_error")\n')
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gcc.register_callback(gcc.PLUGIN_FINISH_UNIT, close_output)
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ps = GdbExceptionChecker(output_file)
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ps.register_after('ssa')
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main()
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