[PATCH 1/5] sim/cgen: mask uninitialized variable warning in cgen-run.c

Andrew Burgess via Gdb-patches
2022-10-12T12:39:06Z

I see an uninitialized variable warning (with gcc 9.3.1) from
cgen-run.c, like this:

/tmp/build/sim/../../src/sim/cris/../common/cgen-run.c: In function ‘sim_resume’:
/tmp/build/sim/../../src/sim/cris/../common/cgen-run.c:259:5: warning: ‘engine_fns$’ may be used uninitialized in this function [-Wmaybe-uninitialized]
259 | (* engine_fns[next_cpu_nr]) (cpu);
| ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/tmp/build/sim/../../src/sim/cris/../common/cgen-run.c:232:14: note: ‘engine_fns$’ was declared here
232 | ENGINE_FN *engine_fns[MAX_NR_PROCESSORS];
| ^~~~~~~~~~

This is a false positive - we over allocate engine_fn, and then only
initialize the nr_cpus entries which we will later go on to use.

However, we can easily silence this warning by initializing the unused
entries in engine_fns to NULL, this might also help if anyone ever
looks at engine_fns in a debugger, it should now be obvious which
entries are in use, and which are not.

With this change the warning is gone.

There should be no change in behaviour with this commit.
---
sim/common/cgen-run.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/sim/common/cgen-run.c b/sim/common/cgen-run.c
index 9a13b0ca416..a9a493c01b9 100644
--- a/sim/common/cgen-run.c
+++ b/sim/common/cgen-run.c
@@ -242,6 +242,11 @@ engine_run_n (SIM_DESC sd, int next_cpu_nr, int nr_cpus, int max_insns, int fast
prime_cpu (cpu, max_insns);
}

+ /* Ensure the remaining engine_fns slots are initialized, this silences a
+ compiler warning when engine_fns is used below. */
+ for (i = nr_cpus; i < MAX_NR_PROCESSORS; ++i)
+ engine_fns[i] = NULL;
+
while (1)
{
SIM_ENGINE_PREFIX_HOOK (sd);
--
2.25.4