[PATCH 2/5] tests default_vmlinux_btf: Introduce test for using BTF by default

[Arnaldo Carvalho de Melo <acme@kernel.org>]

From: Arnaldo Carvalho de Melo <acme@redhat.com>

On a system without any debugging info or when one specifies BTF as the
only BTF info desired but no BTF is available (or invalidated using
PAHOLE_VMLINUX_BTF_FILENAME to an invalid/non-existent file), we're
getting a segfault:

  root@x1:/home/acme/git/pahole# export PAHOLE_VMLINUX_BTF_FILENAME=non-existent
  root@x1:/home/acme/git/pahole# pahole --running_kernel_vmlinux
  pahole: couldn't find a vmlinux that matches the running kernel
  HINT: Maybe you're inside a container or missing a debuginfo package?
  root@x1:/home/acme/git/pahole# pahole
  Segmentation fault (core dumped)
  root@x1:/home/acme/git/pahole#

So add a test that checks for that before we fix it:

  root@x1:/home/acme/git/pahole# tests/default_vmlinux_btf.sh
  Default BTF on a system without BTF: FAILED
  root@x1:/home/acme/git/pahole#

Reported-by: Matthias Schwarzott <zzam@gentoo.org>
Cc: Alan Maguire <alan.maguire@oracle.com>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Song Liu <song@kernel.org>
Cc: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tests/default_vmlinux_btf.sh | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)
 create mode 100755 tests/default_vmlinux_btf.sh

diff --git a/tests/default_vmlinux_btf.sh b/tests/default_vmlinux_btf.sh
new file mode 100755
index 0000000000000000..a9effa2d6d37e0ee
--- /dev/null
+++ b/tests/default_vmlinux_btf.sh
@@ -0,0 +1,21 @@
+#!/bin/bash
+
+echo -n "Default BTF on a system without BTF: "
+
+ulimit -c 0
+
+# To suppress the "Segmentation fault core dumped" message in bash we
+# pipe it to some other command, if it segfaults it will not produce any
+# lines and thus we can infer from the number of lines that the segfault
+# took place, tricky, but couldn't find any other way to check this
+# while suppressing the core dumped message. -acme
+
+nr_lines=$(PAHOLE_VMLINUX_BTF_FILENAME=foobar pahole -F btf list_head 2>&1 | wc -l)
+
+if [ $nr_lines -eq 0 ] ; then
+	echo "FAILED"
+	exit 1
+fi
+
+echo "Ok"
+exit 0
-- 
2.47.0