force pkg-config to only use --prefix when cross-compiling

[eighthave]

The current pkg-config setup has no sense of whether it is cross-compiling, so it will detect things on the build system that are not present or are wrong for the host system. This forces the cross-compiling build to only look for pkg-config .pc files in --prefix.

A version of this has been the setup for many years with the Android builds.

Fixes #32191

Signed-off-by: Hans-Christoph Steiner hans@eds.org

[coveralls]

Pull Request Test Coverage Report for Build 6989

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.001%) to 62.016%

---

Files with Coverage Reduction	New Missed Lines	%
src/feature/hs/hs_common.c	1	84.27%

Totals
Change from base Build 6988:	-0.001%
Covered Lines:	48240
Relevant Lines:	77787

---

💛 - Coveralls

[teor2345]

This test is incorrect: we don't require any particular *.pc file, the user can always set the relevant LIBS and CFLAGS env vars instead.

[eighthave]

libevent is a hard requirement for building, and the idea here is that this is testing that the user ran make install into prefix for libevent. In that case, libevent.pc will be present. Supporting partial installs i.e. not make install into prefix, will waste a lot of time and only achieve flaky results. Also, If there are no .pc files, then there is no point in setting PKG_CONFIG_PATH. And remember, if pkg-config is not properly setup, then --enable-lzma fails without an error on Android builds, and probably other cases too.

[eighthave]

Or in other words, the current tor ./configure setup is a buggy almost unusable mess when it comes to cross-compiling for Android and iOS. There are brittle wrapper build setups that all the related devs are scared to touch at all, so that hinders usage of new functionality like the new modularity. There needs to be one recommended way to build that works reliably, e.g. make install and --prefix on each lib and tor. This is a carefully isolated change that will be easy to avoid for someone who wants to do all sorts of build tricks.

[teor2345]

Tor does not use pkg-config to find libevent:
https://github.com/torproject/tor/blob/master/configure.ac#L751

For libraries where tor does use pkg-config, the pkg-config autotools macros allow the user to manually override the (MODULE)_CLFAGS and (MODULE)_LIBS, as documented in configure's failure messages:
https://github.com/torproject/tor/blob/master/configure.ac#L885

Here is the reference documentation for PKG_CHECK_MODULES():
https://autotools.io/pkgconfig/pkg_check_modules.html

[eighthave]

yes, that's a copy-paste from further below. it works.