(`c2rust-analyze`) Allow calls to `UnknownDef` `KnownFn`s with known ptr perms by kkysen · Pull Request #980 · immunant/c2rust

kkysen · 2023-07-07T11:17:43Z

This allows Callee::UnknownDef calls if they are direct (i.e. not a fn ptr), call a foreign fn (i.e. from an extern block), and are a KnownFn (i.e. returned by const fn all_known_fns). They are treated as normal local fn calls (i.e. they use .visit_local_call, like for Callee::LocalDef) as the PointerIds from the LFnSigs for these foreign fns are constrained by the PermissionSets annotated in the KnownFns. Note that these LFnSigs for the foreign fns are already created by fn gather_foreign_sigs.

I've included a test that checks that a call to libc's access succeeds without crashing and that the pointer passed to it is successfully inferred to be READ | OFFSET_ADD from access's known ptr perms, and thus intended to be rewritten as a slice (though it's not actually rewritten since the foreign fn call is FIXED).

…to `FnSig::inputs_and_output`.

… after gather the non-foreign `fn_sigs` rather than waiting until rewriting. This is needed to use these `LFnSig`s for foreign `fn`s during analysis, which is before rewriting.

c2rust-analyze/src/context.rs

c2rust-analyze/src/known_fn.rs

c2rust-analyze/src/main.rs

c2rust-analyze/src/util.rs

oinoom · 2023-07-07T14:25:06Z

c2rust-analyze/tests/filecheck/known_fn.rs

+}
+
+// CHECK-LABEL: final labeling for "known_fn"
+pub fn known_fn() {


this looks great, are there some more examples you can add here that appear in lighttpd?

Yeah, there'll definitely be more. How many is useful to add here? Are there any particular cases that you think would be helpful to test?

c2rust-analyze/src/known_fn.rs

…ples for now.

…, &'static KnownFn>` set to `all_known_fns()`.

…f `Callee::UnknownDef`.

… before checking each function.

…reign `fn` in `known_fns` as normal local calls now that the `LFnSig`s have ptr perms.

…o `extern "C" fn access` doesn't crash anymore.

…e precise.

c2rust-analyze/src/context.rs

c2rust-analyze/src/dataflow/type_check.rs

c2rust-analyze/src/context.rs

c2rust-analyze/src/util.rs

…ptr_perms`.

…y`s again, not `&LTy`s.

…ally the exact meaning of the `Symbol`s.

… for `KnownFn`s. We specifically want the symbol name. These should normally be the same, but symbol name is more correct. As `SymbolName::name` is a `&str`, I changed `GlobalAnalysisCtxt::known_fns` to store `&'static str` keys instead of `Symbol`s. I also abstracted the symbol name lookup in `fn GlobalAnalysisCtxt::known_fn`, so now `known_fns` is also private.

…ore consistent with `Callee::UnknownDef`.

…recompute the initial `Constraint`s for each function. For now this is just filled with `gacx.known_fn_ptr_perms()`.

…ts` to precompute the initial `Constraint`s for each function. For now this is just filled with `gacx.known_fn_ptr_perms()`." This reverts commit 84d8be4. I found a much simpler way of setting these on the `GlobalAssignment`.

…e `GlobalAssignment` (vs. indirectly through `Constraint`s). This makes it `O(n)` instead of `O(n^2)`, which it was when setting it through `Constraint`s in each function, vs. just once now on the `GlobalAssignment`.

…hange in the `GlobalAssignment`.

c2rust-analyze/src/main.rs

…ady initialized previously. Co-authored-by: spernsteiner <spernsteiner@galois.com>

kkysen added 2 commits July 7, 2023 03:56

(c2rust-analyze) Add {LFnSig,KnownFn}::inputs_and_output similar …

d75bf38

…to `FnSig::inputs_and_output`.

(c2rust-analyze) Move the gather_foreign_sigs call in fn run to…

7079396

… after gather the non-foreign `fn_sigs` rather than waiting until rewriting. This is needed to use these `LFnSig`s for foreign `fn`s during analysis, which is before rewriting.

kkysen requested review from oinoom and spernsteiner July 7, 2023 11:17