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(!) See also [[/glibc/debugging]].

Here are some hints about how to approach testing after nontrivial changes to
glibc have been done.

---

First step is having the build of glibc succeed.  This is actually more
difficult than one might expect as it involves (towards the end of the build
process -- unless you are cross-compiling, of course -- that the
newly created libraries and loader actually work: they'll be used to run the
`rpcgen` program.  If that step doesn't succeed, it'll look similar to this:

    [...]
    CPP='gcc -E -x c-header' [...]/build/elf/ld.so.1 --library-path [...] [...]/build/sunrpc/rpcgen [...]
    Segmentation fault

---

Unless cross-compiling, the next thing you'll probably want to do
is running the test suite, or parts of it.

There is a list of [[known failures|open_issues/glibc]].

---

When building the debian glibc, to save yourself a double-compilation, comment
in debian/sysdeps/hurd-i386.mk the lines about xen. Then to avoid the whole
testsuite, use:

    DEB_BUILD_OPTIONS=nocheck dpkg-buildpackage

To save even more build, stop the build after configure has run, and then you
can restart the build of only libc.so and libc.a with:

    cd build-tree/hurd-i386-libc
    make lib

or of only libc.so with:

    make objdir=$PWD/build-tree/hurd-i386-libc $PWD/build-tree/hurd-i386-libc/libc.so

or of the whole tree with:

    cd build-tree/hurd-i386-libc
    make

or of just one subdir with for instance:

    make subdir=libpthread -C libpthread ..=../ objdir=$PWD/build-tree/hurd-i386-libc

(note that most subdirs need libc.so built)

---

In some cases, printing to stdout/stderr is problematic. One can use a kernel
with kdb enabled, and `mach_print` to get messages on the console:

    #include <mach/mach_traps.h>
    ...
        mach_print("foo\n");

If your `mach_traps.h` does not have the declaration, use:

    extern void mach_print(const char *s);

This call does not support any formatting. You can use this kind of helper to
format a message before passing to gnumach:

    #include <mach/mach_traps.h>
    #include <stdio.h>
    
    static void myprintf(const char *fmt, ...)
    {
      va_list ap;
      char buf[1024];
      va_start(ap, fmt);
      vsnprintf(buf, sizeof(buf), fmt, ap);
      mach_print(buf);
      va_end(ap);
    }

---

If you've been doing simple changes to glibc functions that end up in
`libc.so`, you may test them like this (like for a `strerror_l` implementation
in this case):

    $ LD_PRELOAD=./libc.so ./ld.so ./a.out 10 1073741928 de_DE.utf8
    1073741928 (0x40000068): Computer bought the farm
    1073741928 (0x40000068): Der Computer hat den Bauernhof erworben

You usually will only have luck using the new `libc.so` (from
`[glibc-build]/libc.so`) in combination together with the new `ld.so` (from
`[glibc-build]/elf/ld.so`):

    $ LD_PRELOAD=./libc.so ./a.out 10 1073741928 de_DE.utf8
    Killed
    $ LD_PRELOAD=./libc.so /lib/ld.so ./a.out 10 1073741928 de_DE.utf8
    Killed

Make sure static linking is working OK at all.  Running the
`[glibc-build]/elf/sln` program (a stripped-down `ln` that is statically
linked) ought to test that.  Also, static linking under various conditions will
already have been tested when running the test suite, especially in `elf/` and
`dlfcn/`.

Make sure static linking with cthreads is working.  If you can get an
`ext2fs.static` compiled and linked against the new glibc, that is good.

[TODO].

Then debug its startup as a normal program on your working hurd.

    $ [...]/ext2fs.static --help
    [...]

Then try its full server startup.

    $ settrans -ca node [...]/ext2fs.static BACKING_STORE
    $ ls -l node/
    [...]

Make sure dynamic linking for servers is working.  If you haven't broken the
ABI, you can just use an existing `/hurd/foobar` binary, started the way
glibc's `testrun.sh` does it.

[TODO]: Is this the correct way to do that?

    $ settrans -ca node [glibc]/build/testrun.sh /hurd/ext2fs BACKING_STORE
    $ cd node/
    [...]

---

Test it in a [[subhurd]].

---

Test it on a real system.