Fix some Clang warnings I saw in Clang 22

CMakeLists.txt

@@ -41,6 +41,7 @@ endif()
 
 set(cflags)
 set(priv_cflags)
+set(warn_suppress)
 set(defines)
 set(ldflags)
 set(asm_lang "ASM")
@@ -52,6 +53,23 @@ if(CMU_COMP_GNUC)
   endif()
 endif()
 
+if(CMU_COMP_CLANG)
+  # applied after CMU_FLAGS_W4 (which enables -Weverything), warnings that do
+  # not apply to this code base:
+  list(
+    APPEND warn_suppress
+    # keep -Wno-* below working on clang versions that lack them
+    -Wno-unknown-warning-option
+    # we target C99, mixing declarations and code is intentional
+    -Wno-declaration-after-statement
+    # implementing fibers means doing raw pointer arithmetic on stacks
+    -Wno-unsafe-buffer-usage
+    # C++ compatibility warning triggered by hu_cxx_static_cast(), this
+    # translation unit is always compiled as C
+    -Wno-implicit-void-ptr-cast
+  )
+endif()
+
 if(FIBER_ASM_CHECK_ALIGNMENT)
   list(APPEND defines "-DFIBER_ASM_CHECK_ALIGNMENT=1")
 endif()
@@ -133,7 +151,8 @@ if(FIBER_LTO)
 endif()
 
 target_compile_options(fiber PUBLIC ${cflags})
-target_compile_options(fiber PRIVATE ${priv_cflags} ${CMU_FLAGS_W4})
+target_compile_options(fiber PRIVATE ${priv_cflags} ${CMU_FLAGS_W4}
+                                     ${warn_suppress})
 
 if(ldflags)
   cmu_target_link_options(fiber PUBLIC ${ldflags})

include/fiber/fiber_mach.h

@@ -90,7 +90,7 @@
         void *lr;    /* r30 */                                                 \
         void *fp;    /* r29 */                                                 \
         void *r[10]; /* r19 - r28 */                                           \
-        double d[8]; /* d8 - d15 */
+        double d[8] /* d8 - d15 */
 
 #elif HU_ARCH_RISCV_P && HU_OS_POSIX_P
 #    define FIBER_TARGET_RISCV_ELF 1

src/fiber.c

@@ -57,18 +57,21 @@ stack_align_n(char *sp, size_t n)
     return (char *) ((uintptr_t) sp & ~(uintptr_t) (n - 1));
 }
 
-HU_MAYBE_UNUSED
-bool
+#ifndef NDEBUG
+/* only used in assertions */
+static inline bool
 is_stack_aligned(void *sp)
 {
     return ((uintptr_t) sp & (STACK_ALIGNMENT - 1)) == 0;
 }
+#endif
 
 static inline void
 push(char **sp, void *val)
 {
     *sp -= WORD_SIZE;
-    *(void **) *sp = val;
+    /* sp is kept word aligned, cast via void * to silence -Wcast-align */
+    *(void **) (void *) *sp = val;
 }
 
 typedef struct
@@ -147,7 +150,7 @@ free_pages(void *p)
 
 HU_CONST_FN
 static size_t
-get_page_size()
+get_page_size(void)
 {
     static size_t PAGE_SIZE = 0;
     size_t pgsz = PAGE_SIZE;
@@ -285,10 +288,10 @@ fiber_switch(Fiber *from, Fiber *to)
 #if hu_has_attribute(weak)
 #    define HAVE_probe_stack_weak_dummy
 __attribute__((weak)) void
-_probe_stack_weak_dummy(volatile char *sp, size_t sz);
+fiber_probe_stack_weak_dummy(volatile char *sp, size_t sz);
 
 __attribute__((weak)) void
-_probe_stack_weak_dummy(volatile char *sp, size_t sz)
+fiber_probe_stack_weak_dummy(volatile char *sp, size_t sz)
 {
     (void) sp;
     (void) sz;
@@ -305,13 +308,14 @@ probe_stack(volatile char *sp0, size_t sz, size_t pgsz)
 #endif
     size_t i = 0;
     while (i < sz) {
-        *(volatile uintptr_t *) sp |= (uintptr_t) 0;
+        /* sp is page aligned, cast via void * to silence -Wcast-align */
+        *(volatile uintptr_t *) (volatile void *) sp |= (uintptr_t) 0;
         i += pgsz;
         sp -= pgsz;
     }
 
 #ifdef HAVE_probe_stack_weak_dummy
-    _probe_stack_weak_dummy(sp0, sz);
+    fiber_probe_stack_weak_dummy(sp0, sz);
 #endif
 }
 
@@ -368,7 +372,7 @@ fiber_exec_on(Fiber *active, Fiber *temp, FiberFunc f, void *args)
 }
 
 size_t
-fiber_stack_alignment()
+fiber_stack_alignment(void)
 {
     return STACK_ALIGNMENT;
 }