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bpo-46724: Fix dis support for overflow args #31285

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merged 15 commits into from Feb 18, 2022
Merged

bpo-46724: Fix dis support for overflow args #31285

merged 15 commits into from Feb 18, 2022

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@saulshanabrook
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@saulshanabrook saulshanabrook commented Feb 11, 2022 •
edited

This PR makes dis aware that currently Python's opargs wrap after a certain value. This is used in Python 3.10+ for code which includes negative args to represent negative jumps, like this:

while not (x < y < z):
    pass

which produces this dis output after this PR:

              0 RESUME                   0

  1           2 LOAD_NAME                0 (a)
              4 LOAD_NAME                1 (b)
              6 SWAP                     2
              8 COPY                     2
             10 COMPARE_OP               0 (<)
             12 POP_JUMP_IF_FALSE       11 (to 22)
             14 LOAD_NAME                2 (c)
             16 COMPARE_OP               0 (<)
             18 POP_JUMP_IF_TRUE        28 (to 56)
             20 JUMP_FORWARD             1 (to 24)
        >>   22 POP_TOP
        >>   24 LOAD_NAME                0 (a)
             26 LOAD_NAME                1 (b)
             28 SWAP                     2
             30 COPY                     2
             32 COMPARE_OP               0 (<)
             34 POP_JUMP_IF_FALSE       23 (to 46)
             36 LOAD_NAME                2 (c)
             38 COMPARE_OP               0 (<)
             40 POP_JUMP_IF_FALSE       12 (to 24)
             42 LOAD_CONST               0 (None)
             44 RETURN_VALUE
        >>   46 POP_TOP
             48 EXTENDED_ARG           255
             50 EXTENDED_ARG         65535
             52 EXTENDED_ARG         16777215
             54 JUMP_FORWARD           -16 (to 24)
        >>   56 LOAD_CONST               0 (None)
             58 RETURN_VALUE

Before this PR, the JUMP_FORWARD on line 54 had a huge value that did not match the Python interpreters behavior.

It is unclear to me whether producing this sort of bytecode is intended (I assume it's not), but at least with this fix the dis output more closes matches the current implementation.

https://bugs.python.org/issue46724
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@the-knights-who-say-ni the-knights-who-say-ni commented Feb 11, 2022

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@saulshanabrook saulshanabrook changed the title bpo-46724: Fix dis support for overflow args bpo-46724: Fix dis support for negative args Feb 12, 2022
@saulshanabrook saulshanabrook changed the title bpo-46724: Fix dis support for negative args bpo-46724: Fix dis support for overflow args Feb 12, 2022
saulshanabrook added a commit to metadsl/python-code-data that referenced this issue Feb 12, 2022
@saulshanabrook
Support negative jumps in 3.10
10ec42d 
Adds support for negative relative jump args introduced in Python 3.10.

Ports corresponding fix from dis
python/cpython#31285
@saulshanabrook saulshanabrook mentioned this pull request Feb 12, 2022
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saulshanabrook added a commit to metadsl/python-code-data that referenced this issue Feb 12, 2022
@saulshanabrook
Support negative jumps in 3.10
d06a6da 
Adds support for negative relative jump args introduced in Python 3.10.

Ports corresponding fix from dis
python/cpython#31285
JelleZijlstra
JelleZijlstra reviewed Feb 13, 2022
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@saulshanabrook saulshanabrook commented Feb 13, 2022

@JelleZijlstra Thanks for taking a look.

Would you be able to approve the actions to run on this PR so I can see if the tests pass in CI?

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@JelleZijlstra JelleZijlstra commented Feb 13, 2022

Sorry, I don't have that power.

markshannon
markshannon reviewed Feb 14, 2022
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JelleZijlstra
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markshannon
markshannon reviewed Feb 16, 2022
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# Rely on C `int` being 32 bits for oparg
_INT_BITS = 32
# Maximum value for a c int
_INT_MAX = 2 ** (_INT_BITS - 1)
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@markshannon markshannon Feb 16, 2022

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This is when it overflows, not the maximum value.
Rather than messing around with subtracting one, I'd recommend renaming this to _INT_OVERFLOW.
The math is sound.

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@saulshanabrook saulshanabrook Feb 16, 2022

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Thanks for catching, fixed!

markshannon
markshannon reviewed Feb 16, 2022
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@markshannon markshannon left a comment

One quibble about naming, otherwise looks good.

@saulshanabrook saulshanabrook force-pushed the fix-issue-46724-dis branch from 8ad2b32 to 2ababec Feb 16, 2022
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@JelleZijlstra JelleZijlstra commented Feb 17, 2022

I removed the review requests. In the future, it's better to merge main into the branch instead of rebasing.

Thanks for updating it, I can take another look at the PR later.

@saulshanabrook
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@saulshanabrook saulshanabrook commented Feb 17, 2022

@JelleZijlstra thank you for removing them.

In the future, it's better to merge main into the branch instead of rebasing.

Will do.

JelleZijlstra
JelleZijlstra reviewed Feb 17, 2022
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@markshannon markshannon merged commit c3ce778 into python:main Feb 18, 2022
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@markshannon markshannon commented Feb 18, 2022

Thanks @saulshanabrook

@saulshanabrook saulshanabrook mentioned this pull request Feb 16, 2022
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@saulshanabrook saulshanabrook deleted the fix-issue-46724-dis branch Feb 18, 2022
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