Hi,

I need a little help figuring out how to use gdb in Guix for bug 48941:

  https://debbugs.gnu.org/cgi/bugreport.cgi?bug=48941

Here's the situation.  A libfaketime test hangs forever.  Upstream
suggested I debug it.  I'm trying to, but gdb errors out.  What am I
doing wrong?  It's probably something simple, but I can't see what.

I'll describe what I've done.  First, I started a build like so:

  ./pre-inst-env guix build --keep-failed libfaketime

While the problematic test hung, I found the PID of the test and killed
it.  This caused the build to fail, leaving the build environment for me
to play around in.

I entered a pure environment that contains all the things I need to
debug the test (gcc 10.3.0 is currently the default gcc on
core-updates):

  ./pre-inst-env guix environment --pure libfaketime --ad-hoc gcc-toolchain@10.3.0 gcc-toolchain@10.3.0:debug gdb

In the pure environment, I confirmed I can build and run the hanging
test via the following commands (I added -g in order to get debug
symbols):

  make FAKETIME_COMPILE_CFLAGS='-DFORCE_MONOTONIC_FIX -g' CC=gcc PREFIX=/tmp/guix-build-libfaketime-0.9.9.drv-0/myprefix
  make FAKETIME_COMPILE_CFLAGS='-DFORCE_MONOTONIC_FIX -g' CC=gcc PREFIX=/tmp/guix-build-libfaketime-0.9.9.drv-0/myprefix test

OK, so I can trigger the hang.  Great!  Next step, fire up GDB:

--8<---------------cut here---------------start------------->8---
[0] [env] marusich@suzaku:/tmp/guix-build-libfaketime-0.9.9.drv-0/source/test
$ gdb ./timetest
GNU gdb (GDB) 10.2
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License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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Type "show copying" and "show warranty" for details.
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Type "show configuration" for configuration details.
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<https://www.gnu.org/software/gdb/bugs/>.
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Reading symbols from ./timetest...
(gdb) 
--8<---------------cut here---------------end--------------->8---

The debug symbols provided by gcc-toolchain@10.3.0:debug are under
$GUIX_ENVIRONMENT/lib/debug.  This is the value of GUIX_ENVIRONMENT:

--8<---------------cut here---------------start------------->8---
$ echo $GUIX_ENVIRONMENT
/gnu/store/32fjhp30k34fh0g9f1gmgcj8pc5wldq6-profile
--8<---------------cut here---------------end--------------->8---

By the way, this directory corresponds to glibc 2.33:

--8<---------------cut here---------------start------------->8---
$ realpath /gnu/store/32fjhp30k34fh0g9f1gmgcj8pc5wldq6-profile/lib/debug
/gnu/store/8akrlhc25d7xvi85gzvginw0vdi4zyg4-glibc-2.33-debug/lib/debug
--8<---------------cut here---------------end--------------->8---

Let's tell GDB where to find those debug symbols:

  (gdb) set debug-file-directory /gnu/store/32fjhp30k34fh0g9f1gmgcj8pc5wldq6-profile/lib/debug

Let's also tell GDB to set the environment variables that upstream
recommended when running the test program:

--8<---------------cut here---------------start------------->8---
(gdb) set environment LD_PRELOAD=../src/libfaketime.so.1
(gdb) set environment FAKETIME=-10d
(gdb) set environment NO_FAKE_STAT=1
--8<---------------cut here---------------end--------------->8---

Now run it:

--8<---------------cut here---------------start------------->8---
(gdb) run
Starting program: /tmp/guix-build-libfaketime-0.9.9.drv-0/source/test/timetest 
/bin/sh: /lib/powerpc64le-linux-gnu/libc.so.6: version `GLIBC_2.33' not found (required by ../src/libfaketime.so.1)
/bin/sh: /lib/powerpc64le-linux-gnu/libc.so.6: version `GLIBC_2.32' not found (required by /gnu/store/kmblbljiygayhlc5gb02an9imhy90ws9-glibc-2.33/lib/libpthread.so.0)
/bin/sh: /lib/powerpc64le-linux-gnu/libc.so.6: version `GLIBC_2.32' not found (required by /gnu/store/kmblbljiygayhlc5gb02an9imhy90ws9-glibc-2.33/lib/libdl.so.2)
/bin/sh: /lib/powerpc64le-linux-gnu/libc.so.6: version `GLIBC_2.32' not found (required by /gnu/store/kmblbljiygayhlc5gb02an9imhy90ws9-glibc-2.33/lib/librt.so.1)
During startup program exited with code 1.
(gdb) 
--8<---------------cut here---------------end--------------->8---

Huh?  What happened?  I've double checked that I'm using gdb provided by
Guix:

--8<---------------cut here---------------start------------->8---
$ type -P gdb
/gnu/store/32fjhp30k34fh0g9f1gmgcj8pc5wldq6-profile/bin/gdb
--8<---------------cut here---------------end--------------->8---

I also tried running gdb by invoking it via that absolute file name, and
it still errored out in the same way.

I'm operating in a --pure environment.  All the tools are provided by
Guix.  I'm surprised that /bin/sh and /lib are even mentioned above.

If anyone can provide any advice, I'd be very grateful.  I'm not sure
how to proceed.

-- 
Chris