Hello Steven Rostedt,
Commit dca91c1c5468 ("tracing: Have persistent trace instances save
module addresses") from Mar 5, 2025 (linux-next), leads to the
following Smatch static checker warning:
kernel/trace/trace.c:9422 allocate_trace_buffer()
error: uninitialized symbol 'scratch_size'.
kernel/trace/trace.c
9403 static int
9404 allocate_trace_buffer(struct trace_array *tr, struct array_buffer
*buf, int size)
9405 {
9406 enum ring_buffer_flags rb_flags;
9407 struct trace_scratch *tscratch;
9408 unsigned int scratch_size;
9409
9410 rb_flags = tr->trace_flags & TRACE_ITER_OVERWRITE ?
RB_FL_OVERWRITE : 0;
9411
9412 buf->tr = tr;
9413
9414 if (tr->range_addr_start && tr->range_addr_size) {
9415 /* Add scratch buffer to handle 128 modules */
9416 buf->buffer = ring_buffer_alloc_range(size, rb_flags,
0,
9417
tr->range_addr_start,
9418
tr->range_addr_size,
9419
struct_size(tscratch, entries, 128));
9420
9421 tscratch = ring_buffer_meta_scratch(buf->buffer,
&scratch_size);
--> 9422 setup_trace_scratch(tr, tscratch, scratch_size);
If ring_buffer_alloc_range() fails then scratch_size is uninitialized.
This is "harmless". According to the C standard, it's undefined but in
the kernel we would allow it if setup_trace_scratch() is inlined. Which
it probably will be. The other thing is that if it's not inline the
UBSan detector will complain about these.
The compiler basically always initializes stack variables to zero these
days so adding an "= 0;" doesn't change runtime at all.
9423
9424 /*
9425 * This is basically the same as a mapped buffer,
9426 * with the same restrictions.
9427 */
9428 tr->mapped++;
9429 } else {
9430 buf->buffer = ring_buffer_alloc(size, rb_flags);
9431 }
9432 if (!buf->buffer)
9433 return -ENOMEM;
9434
9435 buf->data = alloc_percpu(struct trace_array_cpu);
9436 if (!buf->data) {
9437 ring_buffer_free(buf->buffer);
9438 buf->buffer = NULL;
9439 return -ENOMEM;
9440 }
9441
9442 /* Allocate the first page for all buffers */
9443 set_buffer_entries(&tr->array_buffer,
9444 ring_buffer_size(tr->array_buffer.buffer,
0));
9445
9446 return 0;
9447 }
regards,
dan carpenter
