ninja-build/ninja

Environment variable with a hyphen is dropped in ubuntu

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#2288 opened on Apr 20, 2023

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bughelp wanted

Description

Feel free to close this as invalid, the bug is likely not in ninja, as it looks like ninja simply does a posix_spawn to launch a process without modifying the environment. Though interestingly I could not reproduce the issue without ninja (tried my own wrapper that does posix_spawn etc), so opening it here as someone else might have experienced the same issue.

populate buid.ninja with

rule environ
    command = env

build env.txt: environ

Run ninja with command:

env - FOO_bar=1 FOO_baz-baz=2 ninja

Expected output from env should include both FOO_bar and FOO_baz-baz variables, but on some systems you will only see the variable without hyphen in the name, those with hyphen are dropped somewhere.

So far I've tested: Ubuntu: Buggy Linux Mint: Buggy Fedora: Works Fine Arch: works Fine

I've also debugged by making ninja printing environ just before doing posix_spawn and I can see the variable FOO_baz-baz there, it just isn't visible in the launched process.

My guess is that ubuntu glibc does something wrong somewhere, but I couldn't find it

Contributor guide

Tech stack
cpp
Domain
build system
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
needs investigation
Prerequisites
C/C++ debuggingPOSIX environment variablesglibc internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
The bug appears to be in how ninja spawns processes via posix spawn, likely in src/subproc.cc or src/build.cc. The issue may be related to glibc's handling of environment variables with hyphens. Investigate the environment variable passing mechanism and test on Ubuntu with a minimal C program. Check if the issue is reproducible outside ninja. Look for any filtering of environment variable names in the codebase. Consider adding a test case for environment variables with special characters.