178 lines
6.2 KiB
Python
178 lines
6.2 KiB
Python
'''
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This module contains helper classes for alignment arithmetic and checks
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'''
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from fractions import gcd
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class Alignment(object):
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def __init__(self, align=4, offset=0):
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self.align = align
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# normalize the offset (just in case)
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self.offset = offset % align
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def __eq__(self, other):
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return self.align == other.align and self.offset == other.offset
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def __str__(self):
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return "(align=%d, offset=%d)" % (self.align, self.offset)
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@staticmethod
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def for_primitive_type(size):
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# compute the required start_alignment based on the size of the type
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if size % 8 == 0:
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# do 8-byte primitives require 8-byte alignment in X11?
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return Alignment(8,0)
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elif size % 4 == 0:
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return Alignment(4,0)
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elif size % 2 == 0:
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return Alignment(2,0)
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else:
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return Alignment(1,0)
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def align_after_fixed_size(self, size):
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new_offset = (self.offset + size) % self.align
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return Alignment(self.align, new_offset)
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def is_guaranteed_at(self, external_align):
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'''
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Assuming the given external_align, checks whether
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self is fulfilled for all cases.
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Returns True if yes, False otherwise.
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'''
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if self.align == 1 and self.offset == 0:
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# alignment 1 with offset 0 is always fulfilled
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return True
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if external_align is None:
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# there is no external align -> fail
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return False
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if external_align.align < self.align:
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# the external align guarantees less alignment -> not guaranteed
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return False
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if external_align.align % self.align != 0:
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# the external align cannot be divided by our align
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# -> not guaranteed
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# (this can only happen if there are alignments that are not
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# a power of 2, which is highly discouraged. But better be
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# safe and check for it)
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return False
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if external_align.offset % self.align != self.offset:
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# offsets do not match
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return False
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return True
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def combine_with(self, other):
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# returns the alignment that is guaranteed when
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# both, self or other, can happen
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new_align = gcd(self.align, other.align)
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new_offset_candidate1 = self.offset % new_align
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new_offset_candidate2 = other.offset % new_align
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if new_offset_candidate1 == new_offset_candidate2:
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new_offset = new_offset_candidate1
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else:
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offset_diff = abs(new_offset_candidate2 - new_offset_candidate1)
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new_align = gcd(new_align, offset_diff)
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new_offset_candidate1 = self.offset % new_align
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new_offset_candidate2 = other.offset % new_align
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assert new_offset_candidate1 == new_offset_candidate2
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new_offset = new_offset_candidate1
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# return the result
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return Alignment(new_align, new_offset)
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class AlignmentLog(object):
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def __init__(self):
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self.ok_list = []
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self.fail_list = []
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self.verbosity = 1
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def __str__(self):
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result = ""
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# output the OK-list
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for (align_before, field_name, type_obj, callstack, align_after) in self.ok_list:
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stacksize = len(callstack)
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indent = ' ' * stacksize
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if self.ok_callstack_is_relevant(callstack):
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if field_name is None or field_name == "":
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result += (" %sok: %s:\n\t%sbefore: %s, after: %s\n"
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% (indent, str(type_obj), indent, str(align_before), str(align_after)))
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else:
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result += (" %sok: field \"%s\" in %s:\n\t%sbefore: %s, after: %s\n"
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% (indent, str(field_name), str(type_obj),
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indent, str(align_before), str(align_after)))
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if self.verbosity >= 1:
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result += self.callstack_to_str(indent, callstack)
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# output the fail-list
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for (align_before, field_name, type_obj, callstack, reason) in self.fail_list:
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stacksize = len(callstack)
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indent = ' ' * stacksize
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if field_name is None or field_name == "":
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result += (" %sfail: align %s is incompatible with\n\t%s%s\n\t%sReason: %s\n"
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% (indent, str(align_before), indent, str(type_obj), indent, reason))
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else:
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result += (" %sfail: align %s is incompatible with\n\t%sfield \"%s\" in %s\n\t%sReason: %s\n"
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% (indent, str(align_before), indent, str(field_name), str(type_obj), indent, reason))
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if self.verbosity >= 1:
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result += self.callstack_to_str(indent, callstack)
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return result
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def callstack_to_str(self, indent, callstack):
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result = "\t%scallstack: [\n" % indent
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for stack_elem in callstack:
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result += "\t %s%s\n" % (indent, str(stack_elem))
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result += "\t%s]\n" % indent
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return result
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def ok_callstack_is_relevant(self, ok_callstack):
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# determine whether an ok callstack is relevant for logging
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if self.verbosity >= 2:
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return True
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# empty callstacks are always relevant
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if len(ok_callstack) == 0:
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return True
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# check whether the ok_callstack is a subset or equal to a fail_callstack
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for (align_before, field_name, type_obj, fail_callstack, reason) in self.fail_list:
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if len(ok_callstack) <= len(fail_callstack):
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zipped = zip(ok_callstack, fail_callstack[:len(ok_callstack)])
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is_subset = all([i == j for i, j in zipped])
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if is_subset:
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return True
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return False
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def ok(self, align_before, field_name, type_obj, callstack, align_after):
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self.ok_list.append((align_before, field_name, type_obj, callstack, align_after))
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def fail(self, align_before, field_name, type_obj, callstack, reason):
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self.fail_list.append((align_before, field_name, type_obj, callstack, reason))
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def append(self, other):
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self.ok_list.extend(other.ok_list)
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self.fail_list.extend(other.fail_list)
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def ok_count(self):
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return len(self.ok_list)
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