ipv4/tcp.c:4234:1: error: the frame size of 1152 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]

[Eric Dumazet]

On Wed, Sep 8, 2021 at 6:48 AM Thorsten Glaser <t.glaser at tarent.de> wrote:
>
> On Tue, 7 Sep 2021, Linus Torvalds wrote:
>
> > The do_tcp_getsockopt() one in tpc.c is a classic case of "lots of
> > different case statements, many of them with their own struct
> > allocations on stack, and all of them disjoint".
>
> Any compiler developers here? AFAIK the compiler knows the lifetime
> of function-local variables, so why not alias the actual memory
> locations and ranges to minimise stack usage?
>

At least on my builds,  do_tcp_getsockopt() uses less than 512 bytes of stack.

Probably because tcp_zerocopy_receive() is _not_ inlined, by pure luck
I suppose.

Perhaps we should use noinline_for_stack here.

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index e8b48df73c852a48e51754ea98b1e08bf024bb9e..437910c096b202420518c9e5e5cd26b2194d8aa2
100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2054,9 +2054,10 @@ static void tcp_zc_finalize_rx_tstamp(struct sock *sk,
 }

 #define TCP_ZEROCOPY_PAGE_BATCH_SIZE 32
-static int tcp_zerocopy_receive(struct sock *sk,
-                               struct tcp_zerocopy_receive *zc,
-                               struct scm_timestamping_internal *tss)
+static noinline_for_stack int
+tcp_zerocopy_receive(struct sock *sk,
+                    struct tcp_zerocopy_receive *zc,
+                    struct scm_timestamping_internal *tss)
 {
        u32 length = 0, offset, vma_len, avail_len, copylen = 0;
        unsigned long address = (unsigned long)zc->address;