On Sat, 2023-12-23 at 18:40 +0800, Hou Tao wrote:
> From: Hou Tao <houtao1@xxxxxxxxxx>
>
> The test uses bpf_prog_get_info_by_fd() to obtain the xlated
> instructions of the program first. Since these instructions have
> already been rewritten by the verifier, the tests then checks whether
> the rewritten instructions are as expected.
>
> Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
Thank you for adding this test, one nitpick below.
[...]
> +#define private(name) SEC(".bss." #name) __hidden __attribute__((aligned(8)))
> +private(kptr) struct bin_data __kptr * ptr;
> +
> +SEC("tc")
> +int kptr_xchg_inline(void *ctx)
> +{
> + void *old;
> +
> + old = bpf_kptr_xchg(&ptr, NULL);
> + if (old)
> + bpf_obj_drop(old);
> +
> + return 0;
> +}
This is highly unlikely, but in theory nothing guarantees that LLVM
would generate code exactly as expected by pattern in test_kptr_xchg_inline().
It would be more fail-proof to use inline assembly and a naked
function instead of C code, e.g.:
SEC("tc")
__naked int kptr_xchg_inline(void)
{
asm volatile (
"r1 = %[ptr] ll;"
"r2 = 0;"
"call %[bpf_kptr_xchg];"
"if r0 == 0 goto 1f;"
"r1 = r0;"
"r2 = 0;"
"call %[bpf_obj_drop_impl];"
"1:"
"r0 = 0;"
"exit;"
:
: __imm_addr(ptr),
__imm(bpf_kptr_xchg),
__imm(bpf_obj_drop_impl)
: __clobber_all
);
}
/* BTF FUNC records are not generated for kfuncs referenced
* from inline assembly. These records are necessary for
* libbpf to link the program. The function below is a hack
* to ensure that BTF FUNC records are generated.
*/
void __btf_root(void)
{
bpf_obj_drop(NULL);
}
wdyt?
