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bpo-34989: python-gdb.py: fix current_line_num() #9889

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merged 2 commits into from
Oct 15, 2018
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bpo-34989: python-gdb.py: fix current_line_num() #9889

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bpo-34989: python-gdb.py: fix current_line_num()
vstinner Oct 15, 2018
37b347b
move an empty line for readability
vstinner Oct 15, 2018
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Tools-Demos/2018-10-15-13-22-28.bpo-34989.hU4fra.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
python-gdb.py now handles errors on computing the line number of a Python
frame.
46 changes: 33 additions & 13 deletions Tools/gdb/libpython.py
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Original file line number Diff line number Diff line change
Expand Up @@ -934,35 +934,50 @@ def current_line_num(self):
if long(f_trace) != 0:
# we have a non-NULL f_trace:
return self.f_lineno
else:
#try:

try:
return self.co.addr2line(self.f_lasti)
#except ValueError:
# return self.f_lineno
except Exception:
# bpo-34989: addr2line() is a complex function, it can fail in many
# ways. For example, it fails with a TypeError on "FakeRepr" if
# gdb fails to load debug symbols. Use a catch-all "except
# Exception" to make the whole function safe. The caller has to
# handle None anyway for optimized Python.
return None

def current_line(self):
'''Get the text of the current source line as a string, with a trailing
newline character'''
if self.is_optimized_out():
return '(frame information optimized out)'

lineno = self.current_line_num()
if lineno is None:
return '(failed to get frame line number)'
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tiny nit: that could also have a blank line after to make it obvious you're returning early.

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I concur, done.


filename = self.filename()
try:
f = open(os_fsencode(filename), 'r')
with open(os_fsencode(filename), 'r') as fp:
lines = fp.readlines()
except IOError:
return None
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Could we maybe return '(failed to read source)' instead of "None" here? That would maybe be more descriptive, what do you think?

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This code mimicks linecache.getline() which is used to render a traceback.

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To be honest, I was also surprised at the first read, and I had to double check when I saw your comment :-D

with f:
all_lines = f.readlines()
# Convert from 1-based current_line_num to 0-based list offset:
return all_lines[self.current_line_num()-1]

try:
# Convert from 1-based current_line_num to 0-based list offset
return lines[lineno - 1]
except IndexError:
return None
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Same here. If we have an index error that means the file did not match. Maybe we should say this to the user?

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Ditto, linecache.getline() behaves the same, and the code mimicks linecache's behaviour.


def write_repr(self, out, visited):
if self.is_optimized_out():
out.write('(frame information optimized out)')
return
out.write('Frame 0x%x, for file %s, line %i, in %s ('
lineno = self.current_line_num()
lineno = str(lineno) if lineno is not None else "?"
out.write('Frame 0x%x, for file %s, line %s, in %s ('
% (self.as_address(),
self.co_filename.proxyval(visited),
self.current_line_num(),
lineno,
self.co_name.proxyval(visited)))
first = True
for pyop_name, pyop_value in self.iter_locals():
Expand All @@ -981,9 +996,11 @@ def print_traceback(self):
sys.stdout.write(' (frame information optimized out)\n')
return
visited = set()
sys.stdout.write(' File "%s", line %i, in %s\n'
lineno = self.current_line_num()
lineno = str(lineno) if lineno is not None else "?"
sys.stdout.write(' File "%s", line %s, in %s\n'
% (self.co_filename.proxyval(visited),
self.current_line_num(),
lineno,
self.co_name.proxyval(visited)))

class PySetObjectPtr(PyObjectPtr):
Expand Down Expand Up @@ -1732,6 +1749,9 @@ def invoke(self, args, from_tty):

filename = pyop.filename()
lineno = pyop.current_line_num()
if lineno is None:
print('Unable to read python frame line number')
return

if start is None:
start = lineno - 5
Expand Down