[PATCH v2 bpf-next 1/8] s390/bpf: Let arch_prepare_bpf_trampoline return program size

[Song Liu <song@xxxxxxxxxx>]

arch_prepare_bpf_trampoline() for s390 currently returns 0 on success. This
is not a problem for regular trampoline. However, struct_ops relies on the
return value to advance "image" pointer:

bpf_struct_ops_map_update_elem() {
    ...
    for_each_member(i, t, member) {
        ...
        err = bpf_struct_ops_prepare_trampoline();
        ...
        image += err;
    }
}

When arch_prepare_bpf_trampoline returns 0 on success, all members of the
struct_ops will point to the same trampoline (the last one).

Fix this by returning the program size in arch_prepare_bpf_trampoline (on
success). This is the same behavior as other architectures.

Signed-off-by: Song Liu <song@xxxxxxxxxx>
Fixes: 528eb2cb87bc ("s390/bpf: Implement arch_prepare_bpf_trampoline()")
Reviewed-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230919060258.3237176-2-song@xxxxxxxxxx
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
---
 arch/s390/net/bpf_jit_comp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 9ed0a13865ca..fd1936a63878 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -2652,7 +2652,7 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image,
 			return -E2BIG;
 	}
 
-	return ret;
+	return tjit.common.prg;
 }
 
 bool bpf_jit_supports_subprog_tailcalls(void)
-- 
2.34.1