Bug #18235: try_var in mkmf.rb recognizes a variable that is not declared

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: ruby 3.1.0dev (2021-09-30T14:50:31Z master 529fc204af) [powerpc-aix7.2.0]
• Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN

[ReiOdaira (Rei Odaira)]

In 524513be399e81bb170ec88aa0d501f33cbde8c3, try_var in mkmf.rb has been modified to recognize a variable that exists but is not declared. What was the rationale behind this change?

In ext/date/extconf.rb, it checks have_var("altzone", "time.h", opt) . Strangely, in AIX, the variable altzone is not declared in time.h but does exist somewhere in the library. As a result, extconf.rb regards altzone as a valid variable, but compile fails because it is not declared. I think the library of AIX is weird, but the logic of try_var looks as weird to me. I thought the intent of have_var/try_var was to pre-check whether the compile succeeds if you use the variable, wasn't it?

In any case, an ad-hoc solution to this particular issue in the date module is just adding #if defined(_AIX) to ext/date/date_core.c, but I'm curious if try_var could lead to other issues in the future.

Thanks,

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed

Applied in changeset git|ea64e742f5feddbdfb6526cd0a54a9986097a34d.

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Revert "mkmf.rb: try linking at try_var" [Bug #18235]

This reverts commit 524513be399e81bb170ec88aa0d501f33cbde8c3,
which can return false positive by existing but unusable symbol,
including functions.