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mul_u64_u64_div_u64: fix the division-by-zero behavior 

The current implementation forces a compile-time 1/0 division, which
generates an undefined instruction (ud2 on x86) rather than a proper
runtime division-by-zero exception.

Change to trigger an actual div-by-0 exception at runtime, consistent with
other division operations.  Use a non-1 dividend to prevent the compiler
from optimizing the division into a comparison.

Link: https://lkml.kernel.org/r/q246p466-1453-qon9-29so-37105116009q@onlyvoer.pbz
Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
Cc: Biju Das <biju.das.jz@bp.renesas.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Weißschuh <linux@weissschuh.net>
Cc: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Cc: David Laight <david.laight.linux@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Nicolas Pitre 2025-06-16 15:22:44 -04:00 committed by Andrew Morton
parent d71b90e5ba
commit e795000e75
1 changed files with 7 additions and 6 deletions
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13
lib/math/div64.c
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@ -212,12 +212,13 @@ u64 mul_u64_u64_div_u64(u64 a, u64 b, u64 c)
#endif
/* make sure c is not zero, trigger exception otherwise */
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdiv-by-zero"
if (unlikely(c == 0))
return 1/0;
#pragma GCC diagnostic pop
/* make sure c is not zero, trigger runtime exception otherwise */
if (unlikely(c == 0)) {
unsigned long zero = 0;
OPTIMIZER_HIDE_VAR(zero);
return ~0UL/zero;
}
int shift = __builtin_ctzll(c);