Description

brianschubert

opened on Jun 29, 2025

Issue body actions

Bug report

Bug description:

This loop can run forever if there's a cycle in the Makefile variable definitions:

cpython/Lib/sysconfig/__main__.py

Line 79 in 5334732

while len(variables) > 0:

To reproduce:

make clean
echo 'foo=$(foo)' > ./Modules/Setup.local
./configure
make  # hangs forever

Or more minimally:

make clean
echo 'foo=$(foo)' > ./Modules/Setup.local
make Makefile
./python -m sysconfig --generate-posix-vars  # hangs forever

Longer cycles are also possible, e.g. v1=$(v2), v2=$(v3), ...., v999=$(v1).

Note that this is less of an issue if the recursive variable definition gets expanded in the Makefile before python -m sysconfig --generate-posix-vars gets invoked. In that case, Make will detect the cycle and exit before the infinite loop occurs.

@serhiy-storchaka you may be interested, this is very similar to #136073

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-136097: Fix sysconfig._parse_makefile() #136166

Activity

1. brianschubert

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   buildThe build process and cross-buildThe build process and cross-build

   topic-sysconfig

   on Jun 29, 2025
2. serhiy-storchaka

   self-assigned this

   on Jun 29, 2025
3. serhiy-storchaka

   added a commit that references this issue on Jul 1, 2025

   pythongh-136097: Fix sysconfig._parse_makefile()

   967214c
4. serhiy-storchaka commented on Jul 1, 2025

   

   serhiy-storchaka

   on Jul 1, 2025

   Member

   More actions

   Thank you for report. This is much complex code, and it is not always clear what behavior is correct.

   Recursive solution fixes the problem of infinite recursion and other bugs, but it introduces other problem -- stack consumption. If you create several hundred forward referencing variables, you can now get RecursionError. It would be possible to solve this using topological sorting, but I am not sure that it is worth to do this.
5. serhiy-storchaka

   added a commit that references this issue on Jul 1, 2025

   pythongh-136097: Fix sysconfig._parse_makefile()

   3888755
6. FFY00

   added a commit that references this issue on Oct 4, 2025

   gh-136097: Fix sysconfig._parse_makefile() (#136166)

   9e3542a
7. danigm

   added a commit that references this issue on Oct 7, 2025

   pythongh-136097: Fix sysconfig._parse_makefile() (python#136166)

   328e5b9
8. StanFromIreland

   closed this as completedon Aug 16, 2026

Issue actions