Commit 6f403d9d authored by Ilya Leoshkevich's avatar Ilya Leoshkevich Committed by Andrii Nakryiko
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libbpf: Make BPF-side of USDT support work on big-endian machines 



BPF_USDT_ARG_REG_DEREF handling always reads 8 bytes, regardless of
the actual argument size. On little-endian the relevant argument bits
end up in the lower bits of val, and later on the code that handles
all the argument types expects them to be there.

On big-endian they end up in the upper bits of val, breaking that
expectation. Fix by right-shifting val on big-endian.

Signed-off-by: default avatarIlya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220407214411.257260-3-iii@linux.ibm.com
parent e1b6df59

tools/lib/bpf/usdt.bpf.h

+3 −0
Original line number Diff line number Diff line
@@ -177,6 +177,9 @@ int bpf_usdt_arg(struct pt_regs *ctx, __u64 arg_num, long *res) 
		err = bpf_probe_read_user(&val, sizeof(val), (void *)val + arg_spec->val_off);

		if (err)

			return err;

#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__

		val >>= arg_spec->arg_bitshift;

#endif

		break;

	default:

		return -EINVAL;