Hi,
Are there known issues with rcu lib?
I tried to remove the VLA from it by calling alloca() and gcc 14.2 on Linux
immediately complains about "array subscript outside array bounds".
$ ninja -C build
ninja: Entering directory `build'
[1/144] Compiling C object lib/librte_rcu.a.p/rcu_rte_rcu_qsbr.c.o
In file included from ../lib/ring/rte_ring_elem.h:20,
from ../lib/rcu/rte_rcu_qsbr.c:17:
In function ‘__rte_ring_dequeue_elems_32’,
inlined from ‘__rte_ring_do_dequeue_elems’ at
../lib/ring/rte_ring_elem_pvt.h:289:3,
inlined from ‘__rte_ring_dequeue_elems’ at
../lib/ring/rte_ring_elem_pvt.h:298:2,
inlined from ‘__rte_ring_do_dequeue_start’ at
../lib/ring/rte_ring_peek_elem_pvt.h:172:3,
inlined from ‘rte_ring_dequeue_bulk_elem_start’ at
../lib/ring/rte_ring_peek.h:237:9,
inlined from ‘rte_rcu_qsbr_dq_reclaim’ at ../lib/rcu/rte_rcu_qsbr.c:392:4:
../lib/ring/rte_ring_elem_pvt.h:176:36: warning: array subscript 2 is outside
array bounds of ‘char[8]’ [-Warray-bounds=]
176 | obj[i + 2] = ring[idx + 2];
| ~~~~~~~~~~~^~~~~~~~~~~~~~~
If I stubbornly ignore the warning and run the test, rcu_qsbr_autotest
segfaults (no surprise given the previous warning).
Wondering if somebody more familiar with that code would like to take a look.
These were the only changes I had made, on latest main (commit
fab31a03ba98e7457284df95dd9eef2223a4ccaa)
$ cat 0001-rcu.patch
>From dc7776a7b918cd96ffce62dd3bfaca85fc449d1b Mon Sep 17 00:00:00 2001
From: Andre Muezerie <andre...@linux.microsoft.com>
Date: Fri, 28 Feb 2025 21:05:25 -0500
Subject: [PATCH] rcu
---
lib/rcu/rte_rcu_qsbr.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/lib/rcu/rte_rcu_qsbr.c b/lib/rcu/rte_rcu_qsbr.c
index dbf31501a6..65037d0217 100644
--- a/lib/rcu/rte_rcu_qsbr.c
+++ b/lib/rcu/rte_rcu_qsbr.c
@@ -323,7 +323,7 @@ int rte_rcu_qsbr_dq_enqueue(struct rte_rcu_qsbr_dq *dq,
void *e)
return 1;
}
- char data[dq->esize];
+ char *data = alloca(dq->esize);
dq_elem = (__rte_rcu_qsbr_dq_elem_t *)data;
/* Start the grace period */
dq_elem->token = rte_rcu_qsbr_start(dq->v);
@@ -386,7 +386,7 @@ rte_rcu_qsbr_dq_reclaim(struct rte_rcu_qsbr_dq *dq,
unsigned int n,
cnt = 0;
- char data[dq->esize];
+ char *data = alloca(dq->esize);
/* Check reader threads quiescent state and reclaim resources */
while (cnt < n &&
rte_ring_dequeue_bulk_elem_start(dq->r, &data,
--
2.34.1
Thanks,
Andre Muezerie
