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bug#44462: Problem with get_multilibs on macOS

From: Jacob Bachmeyer
Subject: bug#44462: Problem with get_multilibs on macOS
Date: Thu, 05 Nov 2020 21:22:19 -0600
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20090807 MultiZilla/ SeaMonkey/1.1.17 Mnenhy/

Fred Wright wrote:
While investigating some issues in the libffi tests, I came across some cases where errors are caused by DejaGnu's get_multilibs function.

First, thank you for reporting this issue. Mac OS X is beyond the set of systems where we can run direct tests, so our awareness of problems with DejaGnu on Mac OS X depends on bug reports from users.

For some unclear reason, this only seems to get invoked for C++ tests, but when it is, there can be a problem, because under some circumstances it invokes the compiler with the -dumpspecs option, which is a gcc-only option that clang chokes on.

The irregular usage with only C++ tests seems very odd to me, and I will look further into this as time permits. This may be a bug in the libffi testsuite or a bug in DejaGnu.

Even when it's using gcc, it bloats the logfile with the verbose -dumpspecs output, in order to determine something of highly questionable value.

That value may be less questionable for some targets, or for tests that need to be run across each multilib target a GCC instance supports.

I traced the results of get_multilibs (as used by the libffi tests) in many macOS versions, and even the "successful" cases seem to have questionably useful results:


The "/usr/." result returned on 10.4, 10.5, and 32-bit 10.6 is the same as what I see on Ubuntu 14.04, CentOS 7, and Fedora 25, though it's not clear to me what it's supposed to represent.

I have a suspicion that this feature is designed to support testing with an "experimental" compiler build that is not installed on the system and may be useless with system compilers generally, or with Apple's compilers specifically, if Apple does not use multilib.

Also note that when I build and test a 32-bit version of libffi on 10.9, the get_multilibs result is still "./x86_64".

As I do not have access to Mac OS X, I cannot directly explain or verify this, but I will look into get_multilibs, in part to document it in a future release.

Since get_multilibs already has code to return an empty string in the "remote" case (where it assumes this function won't work), I just added code to unix.exp to set multitop to "" for all "darwin" targets, thereby short-circuiting almost all og get_multilibs. That certainly fixes the problem with the libffi tests, and doesn't change any non-Mac behavior, though I don't know if that's the ideal fix. The whole get_mutilibs function looks pretty ugly anyway, and it's generally recognized that relying on -dumpspecs is a bad idea.

It is most certainly not ideal. A better solution is probably to add a test to get_multilibs to return an empty string if the compiler is not GCC. Of course, if another compiler pretends to be GCC enough to pass that check, but does not actually implement -dumpspecs, that is not our bug.

This issue on Mac OS X will probably be a known bug in 1.6.3 and fixed in 1.6.4.

I primarily tested my patch against the 1.6.2 release, since the current master won't install from a non-git directory, and also has multiple failures in its own tests (even on Linux). The patch is nearly identical between the 1.6.2 and master cases, anyway.

Are we looking at the same current master? I have commit 3d62df24deedfb3c7c3e396a31b8ce431138eb49 here and all of the tests pass.

****These other problems are potential release blockers for 1.6.3.****
Can you file another bug report with the test failures and more information about these issues?

I can send the current patch, either as a bare email or as an attachment. AFAIK, Savannah doesn't have the pull request / merge request concept.

This will need to be fixed in libgloss.exp, not unix.exp. I am putting my foot down on fixing bugs in DejaGnu's own tree directly instead of hacking around them like that.

-- Jacob

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