probe: fix J-Link swo_read crash when swo_num_bytes() returns a negative value - #2021
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probe: fix J-Link swo_read crash when swo_num_bytes() returns a negative value#2021adityaanikam wants to merge 2 commits into
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…ive value Signed-off-by: adityaanikam <adityanikam9502@gmail.com>
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Actually self._link.swo_num_bytes() does not retrun a negative value (already caught in pylink with error raised). It can however return 0 which is normal when there is no data. When 0 is passed to pylink swo_read() it crashes with IndexError. The required guard should only check for zero value. Please update the code and commit message. |
| try: | ||
| return self._link.swo_read(0, self._link.swo_num_bytes(), True) | ||
| count = self._link.swo_num_bytes() | ||
| if count <= 0: |
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| if count <= 0: | |
| if count == 0: |
RobertRostohar
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Sep 3, 2026
JLinkProbe.swo_read() passed self._link.swo_num_bytes() straight into swo_read() as the count. pylink allocates a ctypes buffer sized to that count; passing 0 (normal when there is no SWO data available) crashes with IndexError, which isn't a JLinkException and so isn't caught by the existing except clause -- it kills the SWV reader thread outright. swo_num_bytes() itself never returns a negative value (pylink validates and raises internally), so the guard only needs to cover zero. Return an empty bytearray() in that case, matching DebugProbe.swo_read's documented return type. Fixes pyocd#2019.
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Good catch, thanks , you're right that swo_num_bytes() can't go negative since pylink validates that internally. Updated the guard to |
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Fixes #2019.
JLinkProbe.swo_read() passed self._link.swo_num_bytes() straight into swo_read() as the count.
pylink allocates a ctypes buffer sized to that count, so passing 0 -- which is normal when no SWO
data is available -- crashes with IndexError, which isn't a JLinkException and so isn't caught by
the existing except clause either; it kills the SWV reader thread outright.
self._link.swo_num_bytes() never returns a negative value (pylink validates and raises internally
if the underlying call fails), so the guard only needs to check for zero, not negative -- thanks to
@RobertRostohar for catching that in review.
Guards the count before the call and returns an empty bytearray() when it's zero, matching
DebugProbe.swo_read's documented return type.
No test added, JLinkProbe's constructor calls into the real J-Link DLL and raises ProbeError if it's
not present, so testing this cleanly would mean bypassing normal construction in a way nothing else
in this codebase does.