[bpf PATCH v3 4/5] bpf, selftests: Add tests for sock_ops load with r9, r8.r7 registers

[John Fastabend]

Loads in sock_ops case when using high registers requires extra logic to
ensure the correct temporary value is used. We need to ensure the temp
register does not use either the src_reg or dst_reg. Lets add an asm
test to force the logic is triggered.

The xlated code is here,

  30: (7b) *(u64 *)(r9 +32) = r7
  31: (61) r7 = *(u32 *)(r9 +28)
  32: (15) if r7 == 0x0 goto pc+2
  33: (79) r7 = *(u64 *)(r9 +0)
  34: (63) *(u32 *)(r7 +916) = r8
  35: (79) r7 = *(u64 *)(r9 +32)

Notice r9 and r8 are not used for temp registers and r7 is chosen.

Acked-by: Song Liu <songliubrav...@fb.com>
Acked-by: Martin KaFai Lau <ka...@fb.com>
Signed-off-by: John Fastabend <john.fastab...@gmail.com>
---
 .../testing/selftests/bpf/progs/test_tcpbpf_kern.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/test_tcpbpf_kern.c 
b/tools/testing/selftests/bpf/progs/test_tcpbpf_kern.c
index f8b13682..6420b61 100644
--- a/tools/testing/selftests/bpf/progs/test_tcpbpf_kern.c
+++ b/tools/testing/selftests/bpf/progs/test_tcpbpf_kern.c
@@ -75,6 +75,13 @@ int bpf_testcb(struct bpf_sock_ops *skops)
                : [skops] "r"(skops)
                :);
 
+       asm volatile (
+               "r9 = %[skops];\n"
+               "r8 = *(u32 *)(r9 +164);\n"
+               "*(u32 *)(r9 +164) = r8;\n"
+               :: [skops] "r"(skops)
+               : "r9", "r8");
+
        op = (int) skops->op;
 
        update_event_map(op);