guard: partially address @ashelkovnykov's comments

rust/ares_guard/c-src/guard.c

@@ -34,7 +34,7 @@ static GD_state gd = {
   .prev_sigbus_sa = { .sa_sigaction = NULL, .sa_flags = 0 },
 };
 
-static guard_result
+static guard_err
 _protect_page(void *address, int prot)
 {
   if (mprotect(address, GD_PAGE_SIZE, prot)) {
@@ -43,18 +43,18 @@ _protect_page(void *address, int prot)
     return guard_mprotect | errno;
   }
 
-  return guard_success;
+  return 0;
 }
 
 // Center the guard page.
-static guard_result
+static guard_err
 _focus_guard()
 {
   uintptr_t stack_p = *gd.stack_pp;
   uintptr_t alloc_p = *gd.alloc_pp;
   uintptr_t old_guard_p = gd.guard_p;
   uintptr_t new_guard_p;
-  guard_result   err = guard_success;
+  guard_err   err = 0;
 
   if (stack_p == 0 || alloc_p == 0) {
     fprintf(stderr, "guard: focus: stack or alloc pointer is null\r\n");
@@ -86,14 +86,14 @@ _focus_guard()
     }
   }
 
-  return guard_success;
+  return 0;
 }
 
 static void
 _signal_handler(int sig, siginfo_t *si, void *unused)
 {
   uintptr_t sig_addr;
-  guard_result err = guard_success;
+  guard_err err = 0;
 
   assert(gd.guard_p);
 
@@ -138,7 +138,7 @@ _signal_handler(int sig, siginfo_t *si, void *unused)
 }
 
 // Registers the same handler function for SIGSEGV and SIGBUS.
-static guard_result
+static guard_err
 _register_handlers()
 {
   struct sigaction sa;
@@ -157,10 +157,10 @@ _register_handlers()
     return guard_sigaction | errno;
   }
 
-  return guard_success;
+  return 0;
 }
 
-guard_result
+guard_err
 guard(
   void *(*f)(void *),
   void *closure,
@@ -169,8 +169,8 @@ guard(
   void **ret
 ) {
   GD_buflistnode  *new_buffer;
-  guard_result err = guard_success;
-  guard_result td_err = guard_success;
+  guard_err err = 0;
+  guard_err td_err = 0;
 
   if (gd.guard_p == 0) {
     assert(gd.buffer_list == NULL);

rust/ares_guard/c-src/guard.h

@@ -10,7 +10,7 @@
 typedef struct GD_buflistnode GD_buflistnode;
 struct GD_buflistnode {
   jmp_buf               buffer;
-  struct GD_buflistnode *next;
+  GD_buflistnode *next;
 };
 
 /**
@@ -19,21 +19,20 @@ struct GD_buflistnode {
  * The flags are bitwise added to the errno of their respective errors.
  */
 typedef enum {
-  guard_success   = 0,          // successful return
   guard_null      = 1,          // null stack or alloc pointer
   guard_signal    = 2,          // invalid signal
   guard_oom       = 3,          // out of memory
   guard_malloc    = 0x10000000, // malloc error flag
   guard_mprotect  = 0x20000000, // mprotect error flag
   guard_sigaction = 0x40000000, // sigaction error flag
-} guard_result;
+} guard_err;
 
 /**
  * @brief Executes the given callback function `f` within the memory arena 
  * between the stack and allocation pointers pointed to by `s_pp` and `a_pp`,
  * with guard page protection. If `f`'s execution succeeds, its result is 
  * written to the return pointer `*ret`. If `f`'s execution triggers an
- * out of memory error or any other `guard_result`, the `guard_result` is
+ * out of memory error or any other `guard_err`, the `guard_err` is
  * returned and `*ret` is left empty. In either case, cleanup is performed
  * before returning.
  * 
@@ -49,14 +48,14 @@ typedef enum {
  * - The caller is responsible for managing any external state the callback
  *   function may mutate.
  * - The callback function may be interrupted in the case of memory exhaustion
- *   or other `guard_result` error (failure to `mprotect`, `malloc`, etc.).
+ *   or other `guard_err` error (failure to `mprotect`, `malloc`, etc.).
  * - `SIGSEGV` signals are expected to be raised only on guard page accesses.
  *
  * Invariants:
  * - A single guard page is installed and maintained in the approximate center
  *   until `crate::guard::call_with_guard` returns.
  * - A return value is only written to `*ret` on successful callback execution.
- * - A `guard_result` is returned, excepting panics or negative assertions.
+ * - A `guard_err` is returned, excepting panics or negative assertions.
  *
  * Enhancements:
  * - Use only a single, static jump buffer variable instead of a linked list.
@@ -70,9 +69,9 @@ typedef enum {
  * @param a_pp A pointer to the allocation pointer location.
  * @param ret A pointer to a location where the callback's result can be stored.
  * 
- * @return A `guard_result` return code.
+ * @return A `guard_err` error code.
  */
-guard_result
+guard_err
 guard(
   void *(*f)(void *),
   void *closure,

rust/ares_guard/src/lib.rs

@@ -4,7 +4,6 @@
 
 include!(concat!(env!("OUT_DIR"), "/bindings.rs"));
 
-pub const GUARD_SUCCESS:   u32 = guard_result_guard_success;
 pub const GUARD_NULL:      u32 = guard_result_guard_null;
 pub const GUARD_SIGNAL:    u32 = guard_result_guard_signal;
 pub const GUARD_OOM:       u32 = guard_result_guard_oom;