On Thu, Dec 14, 2023 at 6:46 PM Alexei Starovoitov alexei.starovoitov@gmail.com wrote:
On Thu, Dec 14, 2023 at 2:56 PM Daniel Xu dxu@dxuuu.xyz wrote:
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(+)
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++)Kumar,
Is this approach reliable? I suspect the compiler can still optimize it. I feel it will be annoying to clean up if folks start using it now, since there won't be a drop in replacement. Every such bpf_assert_if() would need to be manually patched.
If 2nd part of exception is far, how about we add an equivalent of __bpf_assert() macroses with conditional ops in asm, but with extra 'asm volatile goto' that can be used to construct release of resources.
bpf_do_assert_eq(var1, 0) { bpf_spin_unlock(...); } bpf_do_assert_lt(var2, 0) { bpf_spin_unlock(...); }
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;\ + }) + /* Description * Assert that a conditional expression is true. * Returns diff --git a/tools/testing/selftests/bpf/progs/exceptions.c b/tools/testing/selftests/bpf/progs/exceptions.c index 2811ee842b01..1111e852f154 100644 --- a/tools/testing/selftests/bpf/progs/exceptions.c +++ b/tools/testing/selftests/bpf/progs/exceptions.c @@ -203,6 +203,7 @@ __noinline int assert_nz_gfunc(u64 c) volatile u64 cookie = c;
bpf_assert(cookie != 0); + bpf_assert(_EQ(cookie, 2)); return 0; }
we can probably remove bpf_assert_with() and all of the bpf_assert_le|ne|qt|eq|_with()
Users can open code everything: if (!_EQ(foo, bar)) bpf_throw(123);
bpf_assert_if() can work too, but let's call it bpf_do_assert() and use like:
bpf_do_assert(EQ(time, 0)) { // cleanup }