| Message ID | 97ada80f3aaaeb16bf97e31a8fc204513b4fb6a9.1702594357.git.dxu@dxuuu.xyz |
|---|---|
| State | New |
| Headers | show |
| Series | Various BPF exception improvements | expand |
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.
diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h index 1386baf9ae4a..d63f415bef26 100644 --- a/tools/testing/selftests/bpf/bpf_experimental.h +++ b/tools/testing/selftests/bpf/bpf_experimental.h @@ -263,6 +263,17 @@ extern void bpf_throw(u64 cookie) __ksym; */ #define bpf_assert(cond) if (!(cond)) bpf_throw(0); +/* Description + * Assert that a conditional expression is true. If false, runs code in the + * body before throwing. + * Returns + * Void. + * Throws + * An exception with the value zero when the assertion fails. + */ +#define bpf_assert_if(cond) \ + for (int ___i = 0, ___j = !!(cond); !(___j) && !___i; bpf_throw(0), ___i++) + /* Description * Assert that a conditional expression is true. * Returns @@ -272,6 +283,17 @@ extern void bpf_throw(u64 cookie) __ksym; */ #define bpf_assert_with(cond, value) if (!(cond)) bpf_throw(value); +/* Description + * Assert that a conditional expression is true. If false, runs code in the + * body before throwing. + * Returns + * Void. + * Throws + * An exception with the given value when the assertion fails. + */ +#define bpf_assert_with_if(cond, value) \ + for (int ___i = 0, ___j = !!(cond); !(___j) && !___i; bpf_throw(value), ___i++) + /* Description * Assert that LHS is equal to RHS. This statement updates the known value * of LHS during verification. Note that RHS must be a constant value, and
These macros are a temporary stop-gap until bpf exceptions support unwinding acquired entities. Basically these macros act as if they take a callback which only get executed if the assertion fails. Signed-off-by: Daniel Xu <dxu@dxuuu.xyz> --- .../testing/selftests/bpf/bpf_experimental.h | 22 +++++++++++++++++++ 1 file changed, 22 insertions(+)