The configure script incorrectly detects crypt() when it doesn't exist

[madscientist]

Bug report

Bug description:

I'm trying to build Python in a very limited sysroot, with limited functionality. In particular, there is no crypt library in this restricted system.

Unfortunately, Python configure detects that there IS a crypt() and then the build fails:

$ /data/src/python3/Python-3.12.6/configure 'CFLAGS=-march=haswell -mtune=intel -O2 -fPIC -static-libgcc' 'LDFLAGS=-L/data/src/build/x86_64-linux/sysroot/rl84/lib64 -L/data/src/build/x86_64-linux/sysroot/rl84/usr/lib64' --prefix=/data/src/python3/Linux-Release-make/dist --enable-static --without-readline --with-openssl=/data/src/openssl/Linux-Release-make-maximal/dist
  ...
checking for crypt.h... no
 ...
checking for libxcrypt >= 3.1.1... no
checking for library containing crypt_r... no
checking for crypt or crypt_r... yes
  ...
checking for stdlib extension module _crypt... yes
  ...
[ERROR] _crypt failed to import: /data/src/python3/Linux-Release-make/bld.python3/build/lib.linux-x86_64-3.12/_crypt.cpython-312-x86_64-linux-gnu.so: undefined symbol: crypt
  ...
/bin/install -c -m 755 Modules/_crypt.cpython-312-x86_64-linux-gnu.so /data/src/python3/Linux-Release-make/dist/lib/python3.12/lib-dynload/_crypt.cpython-312-x86_64-linux-gnu.so
/bin/install: cannot stat 'Modules/_crypt.cpython-312-x86_64-linux-gnu.so': No such file or directory
make: *** [Makefile:2079: sharedinstall] Error 1

I believe the problem is that this test is insufficient (from configure.ac):

    AC_LINK_IFELSE([AC_LANG_PROGRAM([
        #ifdef HAVE_CRYPT_H
          #include <crypt.h>
        #endif
        #include <unistd.h>
      ], [
        #ifdef HAVE_CRYPT_R
          void *x = crypt_r;
        #else
          void *x = crypt;
        #endif
      ])
    ], [ac_cv_crypt_crypt=yes], [ac_cv_crypt_crypt=no])

If you compile and link the above with CFLAGS=-O2 then the assignment will be optimized away. I think you can force it by changing the test like this:

    AC_LINK_IFELSE([AC_LANG_PROGRAM([
        #ifdef HAVE_CRYPT_H
          #include <crypt.h>
        #endif
        #include <unistd.h>
        volatile void *x;
      ], [
        #ifdef HAVE_CRYPT_R
          x = crypt_r;
        #else
          x = crypt;
        #endif
      ])
    ], [ac_cv_crypt_crypt=yes], [ac_cv_crypt_crypt=no])

If I do this then the link fails as expected even with -O2.

CPython versions tested on:

3.12

Operating systems tested on:

Linux

Linked PRs

• [3.12] gh-123917: Fix crypt check in configure #123952

[zware]

Sounds like a reasonable thing to fix, even if it's not necessarily technically a supported platform. Are you interested in submitting a PR?

[zware]

Note: 3.12 is the last version to actually include the crypt module; it is removed in 3.13. This will make the doing the PR correctly a bit more challenging than it would otherwise be.

[madscientist]

Hm. I have worked around my issue by adding a patch with the above change to my local Python build environment. I don't anticipate taking a new build of Python 3.12.x; the next time I import a Python it will be >=3.13. If this change is not needed there, and I'm the only one who has ever run into this, I'm not sure it's worth trying to create a fix just for that branch.

[vstinner]

I wrote PR gh-123952 to fix the issue in the 3.12 branch.

@madscientist: Would you mind to test the fix in your setup?

[vstinner]

Fixed by 53af5b2.

Thanks for your bug report and your fix @madscientist.

[picnixz]

Closing as completed since this only affected Python 3.12.