[PATCH v3 2/3] prandom: Convert prandom_u32_state() to __always_inline

Ryan Roberts
2026-01-02T13:12:16Z

We will shortly use prandom_u32_state() to implement kstack offset
randomization and some arches need to call it from non-instrumentable
context. Given the function is just a handful of operations and doesn't
call out to any other functions, let's take the easy path and make it
__always_inline.

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
---
include/linux/prandom.h | 19 ++++++++++++++++++-
lib/random32.c | 19 -------------------
2 files changed, 18 insertions(+), 20 deletions(-)

diff --git a/include/linux/prandom.h b/include/linux/prandom.h
index ff7dcc3fa105..e797b3709f5c 100644
--- a/include/linux/prandom.h
+++ b/include/linux/prandom.h
@@ -17,7 +17,24 @@ struct rnd_state {
__u32 s1, s2, s3, s4;
};

-u32 prandom_u32_state(struct rnd_state *state);
+/**
+ * prandom_u32_state - seeded pseudo-random number generator.
+ * @state: pointer to state structure holding seeded state.
+ *
+ * This is used for pseudo-randomness with no outside seeding.
+ * For more random results, use get_random_u32().
+ */
+static __always_inline u32 prandom_u32_state(struct rnd_state *state)
+{
+#define TAUSWORTHE(s, a, b, c, d) ((s & c) << d) ^ (((s << a) ^ s) >> b)
+ state->s1 = TAUSWORTHE(state->s1, 6U, 13U, 4294967294U, 18U);
+ state->s2 = TAUSWORTHE(state->s2, 2U, 27U, 4294967288U, 2U);
+ state->s3 = TAUSWORTHE(state->s3, 13U, 21U, 4294967280U, 7U);
+ state->s4 = TAUSWORTHE(state->s4, 3U, 12U, 4294967168U, 13U);
+
+ return (state->s1 ^ state->s2 ^ state->s3 ^ state->s4);
+}
+
void prandom_bytes_state(struct rnd_state *state, void *buf, size_t nbytes);
void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state);

diff --git a/lib/random32.c b/lib/random32.c
index 24e7acd9343f..d57baf489d4a 100644
--- a/lib/random32.c
+++ b/lib/random32.c
@@ -42,25 +42,6 @@
#include <linux/slab.h>
#include <linux/unaligned.h>

-/**
- * prandom_u32_state - seeded pseudo-random number generator.
- * @state: pointer to state structure holding seeded state.
- *
- * This is used for pseudo-randomness with no outside seeding.
- * For more random results, use get_random_u32().
- */
-u32 prandom_u32_state(struct rnd_state *state)
-{
-#define TAUSWORTHE(s, a, b, c, d) ((s & c) << d) ^ (((s << a) ^ s) >> b)
- state->s1 = TAUSWORTHE(state->s1, 6U, 13U, 4294967294U, 18U);
- state->s2 = TAUSWORTHE(state->s2, 2U, 27U, 4294967288U, 2U);
- state->s3 = TAUSWORTHE(state->s3, 13U, 21U, 4294967280U, 7U);
- state->s4 = TAUSWORTHE(state->s4, 3U, 12U, 4294967168U, 13U);
-
- return (state->s1 ^ state->s2 ^ state->s3 ^ state->s4);
-}
-EXPORT_SYMBOL(prandom_u32_state);
-
/**
* prandom_bytes_state - get the requested number of pseudo-random bytes
*
--
2.43.0