On 10/21/24 15:14, Puranjay Mohan wrote:
Helge Deller <deller@xxxxxx> writes:
On 10/21/24 14:21, Puranjay Mohan wrote:
The bpf_csum_diff() helper has been fixed to return a 16-bit value for
all archs, so now we don't need to mask the result.
...
--- a/tools/testing/selftests/bpf/progs/verifier_array_access.c
+++ b/tools/testing/selftests/bpf/progs/verifier_array_access.c
@@ -368,8 +368,7 @@ __naked void a_read_only_array_2_1(void)
r4 = 0; \
r5 = 0; \
call %[bpf_csum_diff]; \
-l0_%=: r0 &= 0xffff; \
- exit; \
+l0_%=: exit; \
Instead of dropping the masking, would it make sense to
check here if (r0 >> 16) == 0 ?
We define the expected value in R0 to be 65507(0xffe3) in the line at the top:
__success __retval(65507)
So, we should just not do anything to R0 and it should contain this value
after returning from bpf_csum_diff()
This masking hack was added in:
6185266c5a853 ("selftests/bpf: Mask bpf_csum_diff() return value to 16 bits in test_verifier")
because without the fix in patch 2 bpf_csum_diff() would return the
following for this test:
x86 : -29 : 0xffffffe3
generic (arm64, riscv) : 65507 : 0x0000ffe3
You're right.
Thanks for explaining.
Helge
