From f3c4463f51ec6fb78b52818572b57f86b14db58b Mon Sep 17 00:00:00 2001 From: John Naylor Date: Wed, 21 Jan 2026 15:21:31 +0700 Subject: [PATCH v2 2/2] Future-proof sort template against undefined behavior Commit XXXYYYZZZ added a NULL array pointer check before performing a qsort in order to prevent undefined behavior when passing NULL pointer and zero length. To head off future degenerate cases, check that there are at least two elements to sort before proceeding with insertion sort. This has the added advantage of allowing us to remove four equivalent checks that guarded against recursion/iteration. There might be a tiny performance penalty from unproductive recursions, but we can buy that back by increasing the insertion sort threshold. That is left for future work. Discussion: https://postgr.es/m/777bd201-6e3a-4da0-a922-4ea9de46a3ee@gmail.com --- src/include/lib/sort_template.h | 40 +++++++++++++++++---------------- 1 file changed, 21 insertions(+), 19 deletions(-) diff --git a/src/include/lib/sort_template.h b/src/include/lib/sort_template.h index e02aa73cd4d..22b2092d03b 100644 --- a/src/include/lib/sort_template.h +++ b/src/include/lib/sort_template.h @@ -311,6 +311,14 @@ loop: DO_CHECK_FOR_INTERRUPTS(); if (n < 7) { + /* + * Not strictly necessary, but a caller may pass a NULL pointer input + * and zero length, and this silences warnings about applying offsets + * to NULL pointers. + */ + if (n < 2) + return; + for (pm = a + ST_POINTER_STEP; pm < a + n * ST_POINTER_STEP; pm += ST_POINTER_STEP) for (pl = pm; pl > a && DO_COMPARE(pl - ST_POINTER_STEP, pl) > 0; @@ -387,29 +395,23 @@ loop: if (d1 <= d2) { /* Recurse on left partition, then iterate on right partition */ - if (d1 > ST_POINTER_STEP) - DO_SORT(a, d1 / ST_POINTER_STEP); - if (d2 > ST_POINTER_STEP) - { - /* Iterate rather than recurse to save stack space */ - /* DO_SORT(pn - d2, d2 / ST_POINTER_STEP) */ - a = pn - d2; - n = d2 / ST_POINTER_STEP; - goto loop; - } + DO_SORT(a, d1 / ST_POINTER_STEP); + + /* Iterate rather than recurse to save stack space */ + /* DO_SORT(pn - d2, d2 / ST_POINTER_STEP) */ + a = pn - d2; + n = d2 / ST_POINTER_STEP; + goto loop; } else { /* Recurse on right partition, then iterate on left partition */ - if (d2 > ST_POINTER_STEP) - DO_SORT(pn - d2, d2 / ST_POINTER_STEP); - if (d1 > ST_POINTER_STEP) - { - /* Iterate rather than recurse to save stack space */ - /* DO_SORT(a, d1 / ST_POINTER_STEP) */ - n = d1 / ST_POINTER_STEP; - goto loop; - } + DO_SORT(pn - d2, d2 / ST_POINTER_STEP); + + /* Iterate rather than recurse to save stack space */ + /* DO_SORT(a, d1 / ST_POINTER_STEP) */ + n = d1 / ST_POINTER_STEP; + goto loop; } } #endif -- 2.52.0