[PATCH 1/4] libctf: fix assertion failure with no system qsort_r

[Nick Alcock <nick.alcock@oracle.com>]

If no suitable qsort_r is found in libc, we fall back to an
implementation in ctf-qsort.c.  But this implementation routinely calls
the comparison function with two identical arguments. The comparison
function that ensures that the order of output types is stable is not
ready for this, misinterprets it as a type appearing more that once (a
can-never-happen condition) and fails with an assertion failure.

Fixed, audited for further instances of the same failure (none found)
and added a no-qsort test to my regular testsuite run.

libctf/:
	PR libctf/30013
	* ctf-dedup.c (sort_output_mapping): Inputs are always equal to
	themselves.
---
 libctf/ctf-dedup.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/libctf/ctf-dedup.c b/libctf/ctf-dedup.c
index c46f69e7449..6297c45c84d 100644
--- a/libctf/ctf-dedup.c
+++ b/libctf/ctf-dedup.c
@@ -2306,6 +2306,10 @@ sort_output_mapping (const ctf_next_hkv_t *one, const ctf_next_hkv_t *two,
   ctf_id_t one_type;
   ctf_id_t two_type;
 
+  /* Inputs are always equal to themselves.  */
+  if (one == two)
+    return 0;
+
   one_gid = ctf_dynhash_lookup (d->cd_output_first_gid, one_hval);
   two_gid = ctf_dynhash_lookup (d->cd_output_first_gid, two_hval);
 
-- 
2.39.1.268.g9de2f9a303