On Fri, Dec 16, 2022 at 6:17 PM Eduard Zingerman <eddyz87@xxxxxxxxx> wrote:
>
> A set of macros useful for writing naked BPF functions using inline
> assembly. E.g. as follows:
>
> struct map_struct {
> ...
> } map SEC(".maps");
>
> SEC(...)
> __naked int foo_test(void)
> {
> asm volatile(
> "r0 = 0;"
> "*(u64*)(r10 - 8) = r0;"
> "r1 = %[map] ll;"
> "r2 = r10;"
> "r2 += -8;"
> "call %[bpf_map_lookup_elem];"
> "r0 = 0;"
> "exit;"
> :
> : __imm(bpf_map_lookup_elem),
> __imm_addr(map)
> : __clobber_all);
> }
>
> Signed-off-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
> ---
> tools/testing/selftests/bpf/progs/bpf_misc.h | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/progs/bpf_misc.h b/tools/testing/selftests/bpf/progs/bpf_misc.h
> index a42363a3fef1..bbf56ad95636 100644
> --- a/tools/testing/selftests/bpf/progs/bpf_misc.h
> +++ b/tools/testing/selftests/bpf/progs/bpf_misc.h
> @@ -8,6 +8,12 @@
> #define __log_level(lvl) __attribute__((btf_decl_tag("comment:test_log_level="#lvl)))
> #define __test_state_freq __attribute__((btf_decl_tag("comment:test_state_freq")))
>
> +/* Convenience macro for use with 'asm volatile' blocks */
> +#define __naked __attribute__((naked))
> +#define __clobber_all "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7", "r8", "r9", "memory"
I found that this one doesn't work well when passing some inputs as
registers (e.g., for address of a variable on stack). Compiler
complains that it couldn't find any free registers to use. So I ended
up using
#define __asm_common_clobbers "r0", "r1", "r2", "r3", "r4", "r5", "memory"
and adding "r6", "r7", etc manually, depending on the test.
So maybe let's add it upfront as `__clobber_common` as well?
But changes look good to me:
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> +#define __imm(name) [name]"i"(name)
> +#define __imm_addr(name) [name]"i"(&name)
> +
> #if defined(__TARGET_ARCH_x86)
> #define SYSCALL_WRAPPER 1
> #define SYS_PREFIX "__x64_"
> --
> 2.38.2
>
