From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Tue, 22 Oct 2019 19:29:48 +0000 (-0400)
Subject: Fix: uninitialized variable in lib_ring_buffer_reserve_committed
X-Git-Tag: v2.12.0-rc1~12
X-Git-Url: http://git.liburcu.org/?p=lttng-ust.git;a=commitdiff_plain;h=730be651d21f3950980fd61e1c65953017c6322e

Fix: uninitialized variable in lib_ring_buffer_reserve_committed

This internal function implemented in libringbuffer is not used within
lttng-ust actually, but uses an uninitialized variable:

As reported by clang:

        ./frontend_internal.h:263:75: warning: variable 'idx' is uninitialized when used here [-Wuninitialized]
                struct commit_counters_hot *cc_hot = shmp_index(handle, buf->commit_hot, idx);
                                                                                         ^~~
        ./shm.h:74:86: note: expanded from macro 'shmp_index'
                        ____ptr_ret = (__typeof__(____ptr_ret)) _shmp_offset((handle)->table, &(ref)._ref, index, sizeof(*____ptr_ret));        \
                                                                                                           ^~~~~
        ./frontend_internal.h:262:27: note: initialize the variable 'idx' to silence this warning
                unsigned long offset, idx, commit_count;
                                         ^
                                          = 0
        In file included from ring_buffer_backend.c:29:
        In file included from ./backend.h:33:
        ./frontend_internal.h:263:75: warning: variable 'idx' is uninitialized when used here [-Wuninitialized]
                struct commit_counters_hot *cc_hot = shmp_index(handle, buf->commit_hot, idx);
                                                                                         ^~~
        ./shm.h:74:86: note: expanded from macro 'shmp_index'
                        ____ptr_ret = (__typeof__(____ptr_ret)) _shmp_offset((handle)->table, &(ref)._ref, index, sizeof(*____ptr_ret));        \
                                                                                                           ^~~~~
        ./frontend_internal.h:262:27: note: initialize the variable 'idx' to silence this warning
                unsigned long offset, idx, commit_count;
                                         ^
                                          = 0

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---

diff --git a/libringbuffer/frontend_internal.h b/libringbuffer/frontend_internal.h
index 4ad921ec..1a9c2d4b 100644
--- a/libringbuffer/frontend_internal.h
+++ b/libringbuffer/frontend_internal.h
@@ -260,14 +260,11 @@ int lib_ring_buffer_reserve_committed(const struct lttng_ust_lib_ring_buffer_con
 				      struct lttng_ust_shm_handle *handle)
 {
 	unsigned long offset, idx, commit_count;
-	struct commit_counters_hot *cc_hot = shmp_index(handle, buf->commit_hot, idx);
+	struct commit_counters_hot *cc_hot;
 
 	CHAN_WARN_ON(chan, config->alloc != RING_BUFFER_ALLOC_PER_CPU);
 	CHAN_WARN_ON(chan, config->sync != RING_BUFFER_SYNC_PER_CPU);
 
-	if (caa_unlikely(!cc_hot))
-		return 0;
-
 	/*
 	 * Read offset and commit count in a loop so they are both read
 	 * atomically wrt interrupts. By deal with interrupt concurrency by
@@ -279,6 +276,9 @@ int lib_ring_buffer_reserve_committed(const struct lttng_ust_lib_ring_buffer_con
 	do {
 		offset = v_read(config, &buf->offset);
 		idx = subbuf_index(offset, chan);
+		cc_hot = shmp_index(handle, buf->commit_hot, idx);
+		if (caa_unlikely(!cc_hot))
+			return 0;
 		commit_count = v_read(config, &cc_hot->cc);
 	} while (offset != v_read(config, &buf->offset));