CLEANUP: mux-h2: clarify that bptr is not NULL when calling to h2_get_buf()

In h2_frt_transfer_data(), we first check h2s_rxbuf_tail() and if it's
NULL, we get out. A bit later we pass that function's return to
h2_get_buf(), which dereferences it. It's OK since it was checked. But
depending on optimization levels and tiny extra fixes, gcc-9.5 (at least)
sometimes thinks it sees a possible null-deref and emits a warning. Let's
just use the known safe version of h2s_rxbuf_tail() since we know for sure
that the pointer is valid so that the compiler is no longer confused. A
comment was added at the top of the function to clarify that the pointer
may not be NULL.

diff --git a/src/mux_h2.c b/src/mux_h2.c
index 355ec837d28ab63c55b1c5bb7aef8cd76720a034..95984aa48952de902c012fc302507da7ed61ec7d 100644 (file)
--- a/src/mux_h2.c
+++ b/src/mux_h2.c
@@ -1296,6 +1296,7 @@ static int h2_buf_available(void *target)
        return 0;
 }
 
+/* note that bptr may not be NULL here */
 static inline struct buffer *h2_get_buf(struct h2c *h2c, struct buffer *bptr)
 {
        struct buffer *buf = NULL;
@@ -6640,7 +6641,7 @@ static int h2_frt_transfer_data(struct h2s *h2s)
 
  next_buffer:
        /* now we have a non-full rxbuf */
-       scbuf = h2_get_buf(h2c, h2s_rxbuf_tail(h2s));
+       scbuf = h2_get_buf(h2c, _h2s_rxbuf_tail(h2s));
        if (!scbuf) {
                h2c->flags |= H2_CF_DEM_SALLOC;
                TRACE_STATE("waiting for an h2s rxbuf", H2_EV_RX_FRAME|H2_EV_RX_DATA|H2_EV_H2S_BLK, h2c->conn, h2s);