The weavec.h header

weavec.h declares the one annotation WeaveC has: WEAVEC_UNSAFE. weavec-cc puts the header on the system include path (#include <weavec.h>) and defines __WEAVEC__ to 1 in every unit it compiles with WeaveC enabled. The header is at version 1.0 (WEAVEC_H_VERSION_MAJOR, WEAVEC_H_VERSION_MINOR).

WEAVEC_UNSAFE expands to __attribute__((annotate("weavec.unsafe"))) under compilers that understand Clang’s annotate attribute and to nothing under the others, so code that uses it stays buildable with any C toolchain. Copy the header into a project that must also build without WeaveC installed.

Form	Placement	Meaning
WEAVEC_UNSAFE void f(…) { … }	before a function definition	The function’s body is an unsafe region.
WEAVEC_UNSAFE { … }	before a compound statement	The block is an unsafe region.

In an unsafe region weavec-cc does not guard memory accesses and does not check array indexes (RFC 0035 §2.6, amendment 8). A region is decided by source location: code inlined into it from elsewhere keeps its guards, and the runtime’s allocator still validates every free made in it. The enforcement ledger records each access in a region as unguarded with the reason unsafe.

#include <stdint.h>
#include <weavec.h>

WEAVEC_UNSAFE void write_register(uintptr_t address, uint32_t value) {
  *(volatile uint32_t *)address = value;
}

unsigned long first_word(const char *s) {
  unsigned long word;
  WEAVEC_UNSAFE {
    word = *(const unsigned long *)s; /* may read past the string on purpose */
  }
  return word;
}

A function kept from AddressSanitizer (__attribute__((no_sanitize("address"))), no_sanitize_address or disable_sanitizer_instrumentation) is an unsafe region too, with no source change.

Every other annotation of earlier versions (WEAVEC_OWNED, WEAVEC_BORROWED, WEAVEC_COUNTED_BY, WEAVEC_ASSUME and the rest) was deleted with the ownership analysis that read it (RFC 0036); a program that still uses one fails to compile until it stops. annotate payloads that do not start with weavec. are ignored. The unsafe boundaries guide says when a region is the right tool.