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bpo-38115: Deal with invalid bytecode offsets in lnotab (GH-16079)

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Document that lnotab can contain invalid bytecode offsets (because of
terrible reasons that are difficult to fix). Make dis.findlinestarts()
ignore invalid offsets in lnotab. All other uses of lnotab in CPython
(various reimplementations of addr2line or line2addr in Python, C and gdb)
already ignore this, because they take an address to look for, instead.

Add tests for the result of dis.findlinestarts() on wacky constructs in
test_peepholer.py, because it's the easiest place to add them.
This commit is contained in:
T. Wouters 2019-09-28 16:49:15 +02:00 • committed by Gregory P. Smith
parent 7774d7831e
commit c8165036f3
4 changed files with 77 additions and 2 deletions
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5
Lib/dis.py
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@ -454,6 +454,7 @@ def findlinestarts(code):
"""
byte_increments = code.co_lnotab[0::2]
line_increments = code.co_lnotab[1::2]
bytecode_len = len(code.co_code)
lastlineno = None
lineno = code.co_firstlineno
@ -464,6 +465,10 @@ def findlinestarts(code):
yield (addr, lineno)
lastlineno = lineno
addr += byte_incr
if addr >= bytecode_len:
# The rest of the lnotab byte offsets are past the end of
# the bytecode, so the lines were optimized away.
return
if line_incr >= 0x80:
# line_increments is an array of 8-bit signed integers
line_incr -= 0x100