On Thu, Dec 14, 2023 at 7:10 PM Alexei Starovoitov alexei.starovoitov@gmail.com wrote:
Just realized that we can go the other way instead.
We can get rid of bpf_assert_eq/ne/... and replace with:
diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h index 1386baf9ae4a..1c500287766d 100644 --- a/tools/testing/selftests/bpf/bpf_experimental.h +++ b/tools/testing/selftests/bpf/bpf_experimental.h @@ -254,6 +254,15 @@ extern void bpf_throw(u64 cookie) __ksym; } \ })
+#define _EQ(LHS, RHS) \
({ int var = 1;\asm volatile goto("if %[lhs] == %[rhs] goto %l[l_yes]" \:: [lhs] "r"(LHS), [rhs] "i"(RHS) :: l_yes);\var = 0;\+l_yes:\
var;\})
Realized we can do much better. We can take advantage that bpf assembly syntax resembles C and do:
bpf_assert(CMP(cookie, "!=", 0);
and use it as generic "volatile compare" that compiler cannot optimize out:
Replacing: if (foo < bar) ... with if (CMP(foo, "<", bar)) ... when the compare operator should be preserved. I'll try to prototype it soon.
Might go further and use C++ for bpf programs :) Override operator<, opreator==, ... then if (foo < bar) will be in asm code as written in C++ bpf prog.