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GH-125174: Mark objects as statically allocated. #127797

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Merged
merged 11 commits into from
Dec 11, 2024

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markshannon
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@markshannon markshannon commented Dec 10, 2024

This PR is a follow up to #125251 which made checking for immortal objects more robust.

This adds the ability to check whether objects are statically allocated or not, which should assist finalization and safety checks.

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@ericsnowcurrently ericsnowcurrently left a comment

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Mostly LGTM. I've left a couple of minor comments. This will be a nice improvement.

@ZeroIntensity
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Out of curiosity, how disruptive is adding a new field to the object structure?

@markshannon
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Out of curiosity, how disruptive is adding a new field to the object structure?

It doesn't change the size of the PyObject struct or the offsets of ob_refcnt and ob_type.
Changing any of those would be very disruptive.

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LGTM

@markshannon markshannon merged commit bc262de into python:main Dec 11, 2024
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@AlexWaygood
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This appears to be causing lots of compiler warnings on Windows. Here's what the "Files changed tab looks like on this PR:
image

These warnings are now showing up on the "files changed" tab on every PR

#if SIZEOF_VOID_P > 4
/* If an object has been freed, it will have a negative full refcnt
* If it has not it been freed, will have a very large refcnt */
if (op->ob_refcnt_full <= 0 || op->ob_refcnt > (UINT32_MAX - (1<<20))) {
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Apparently UINT32_MAX is not defined in all builds, so this breaks a buildbot.

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We use UINT32_MAX all over the place, so it must be defined. Maybe we're missing a #include somewhere.

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Looks like it's a C++ build that failing, which might explain it

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srinivasreddy pushed a commit to srinivasreddy/cpython that referenced this pull request Jan 8, 2025
* Set a bit in the unused part of the refcount on 64 bit machines and the free-threaded build.

* Use the top of the refcount range on 32 bit machines
@markshannon markshannon deleted the refcnt-with-flags branch January 10, 2025 16:23
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5 participants