go-pathrs: fix build failure with Clang

.github/workflows/bindings-go.yml

@@ -76,6 +76,11 @@ jobs:
           - "1.18"
           - "oldstable"
           - "stable"
+        # CGo's handling of C constants differs between compilers, so make sure
+        # the bindings build with both of the mainstream C compilers.
+        cc:
+          - gcc
+          - clang
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v7
@@ -92,7 +97,11 @@ jobs:
           go-version: ${{ matrix.go-version }}
           check-latest: true
       # Run smoke-tests.
+      # NOTE: CC is only set here (and not for the whole job) so that we don't
+      #       affect how libpathrs itself is built.
       - run: make -C examples/go smoke-test
+        env:
+          CC: ${{ matrix.cc }}
 
   go-complete:
     needs:

CHANGELOG.md

@@ -11,6 +11,11 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
   library installation were incorrectly called `--disable-dynamic` rather than
   autoconf's `--disable-shared`. We have added new `--{enable,disable}-shared`
   flags and the old ones are kept for compatibility.
+- go-pathrs: Fix a build failure when building the Go bindings with Clang.
+  CGo's handling of the signedness of C constants is compiler-dependent, and
+  the internal sanity check of the `PATHRS_PROC_*` values only handled the way
+  GCC does it (which made Clang builds fail with "untyped int constant
+  ... overflows"). (#401)
 
 ## [0.2.5] - 2026-06-17 ##
 

go-pathrs/internal/libpathrs/libpathrs_linux.go

@@ -219,10 +219,12 @@ func InRootHardlink(oldRootFd uintptr, oldPath string, newRootFd uintptr, newPat
 // ProcBase is pathrs_proc_base_t (uint64_t).
 type ProcBase C.pathrs_proc_base_t
 
-// FIXME: We need to open-code the constants because CGo unfortunately will
-// implicitly convert any non-literal constants (i.e. those resolved using gcc)
-// to signed integers. See <https://github.com/golang/go/issues/39136> for some
-// more information on the underlying issue (though.
+// FIXME: We need to open-code the constants because CGo's handling of
+// non-literal constants (i.e. those resolved using the C compiler) that don't
+// fit in an int64 is compiler-dependent -- GCC gives us implicitly-converted
+// (negative) signed integers while Clang gives us the actual unsigned values.
+// See <https://github.com/golang/go/issues/39136> for some more information on
+// the underlying issue.
 const (
 	// ProcRoot is PATHRS_PROC_ROOT.
 	ProcRoot ProcBase = 0xFFFF_FFFE_7072_6F63 // C.PATHRS_PROC_ROOT
@@ -246,25 +248,36 @@ func assertEqual[T comparable](a, b T, msg string) {
 	}
 }
 
+// u64Mask is used to convert the C constants below into plain uint64 values,
+// regardless of how CGo decided to interpret their signedness.
+//
+// As explained above, CGo gives us the PATHRS_PROC_* values as negative
+// (signed) constants with GCC and as (unsigned) constants that overflow int64
+// with Clang, so neither int64 nor uint64 can hold them with both compilers.
+// However, Go constant expressions are arbitrary-precision and bitwise
+// operations on negative constants operate on their infinite two's complement
+// representation, so masking off the lower 64 bits yields the same uint64
+// value no matter which compiler CGo used.
+const u64Mask = 0xFFFF_FFFF_FFFF_FFFF
+
 // Verify that the values above match the actual C values. Unfortunately, Go
-// only allows us to forcefully cast int64 to uint64 if you use a temporary
-// variable, which means we cannot do it in a const context and thus need to do
-// it at runtime (even though it is a check that fundamentally could be done at
+// has no way of doing compile-time assertions, so we need to do it at runtime
+// (even though it is a check that fundamentally could be done at
 // compile-time)...
 func init() {
 	var (
-		actualProcRoot       int64 = C.PATHRS_PROC_ROOT
-		actualProcSelf       int64 = C.PATHRS_PROC_SELF
-		actualProcThreadSelf int64 = C.PATHRS_PROC_THREAD_SELF
+		actualProcRoot       uint64 = C.PATHRS_PROC_ROOT & u64Mask
+		actualProcSelf       uint64 = C.PATHRS_PROC_SELF & u64Mask
+		actualProcThreadSelf uint64 = C.PATHRS_PROC_THREAD_SELF & u64Mask
 	)
 
 	assertEqual(ProcRoot, ProcBase(actualProcRoot), "PATHRS_PROC_ROOT")
 	assertEqual(ProcSelf, ProcBase(actualProcSelf), "PATHRS_PROC_SELF")
 	assertEqual(ProcThreadSelf, ProcBase(actualProcThreadSelf), "PATHRS_PROC_THREAD_SELF")
 
 	var (
-		actualProcBaseTypeMask uint64 = C.__PATHRS_PROC_TYPE_MASK
-		actualProcBaseTypePid  uint64 = C.__PATHRS_PROC_TYPE_PID
+		actualProcBaseTypeMask uint64 = C.__PATHRS_PROC_TYPE_MASK & u64Mask
+		actualProcBaseTypePid  uint64 = C.__PATHRS_PROC_TYPE_PID & u64Mask
 	)
 
 	assertEqual(ProcBaseTypeMask, ProcBase(actualProcBaseTypeMask), "__PATHRS_PROC_TYPE_MASK")