Use precise size for sigset_t. NFC (#26574)

Author: sbc100

system/lib/libc/musl/arch/emscripten/bits/alltypes.h

@@ -400,8 +400,15 @@ typedef struct __locale_struct * locale_t;
 #endif
 
 
+// Musl uses 128 bytes for sigset_t, presumably for some kind of ABI
+// compatability with the kernel or GLIBC, but in emscripten we can be precise.
+// Since we have _NSIG = 65 which only need 2 `long`s for the bitmask.
+// The signals we support are
+// 1 - 31 - standard POSIX signals (see emscripten/bits/signal.h)
+// 32 - 34 - pthread-specific signals (see pthread_impl.h>
+// 35 - 65 - user-defined RT signals (we don't currently have any test coverage of these).
 #if defined(__NEED_sigset_t) && !defined(__DEFINED_sigset_t)
-typedef struct __sigset_t { unsigned long __bits[128/sizeof(long)]; } sigset_t;
+typedef struct __sigset_t { unsigned long __bits[2]; } sigset_t;
 #define __DEFINED_sigset_t
 #endif
 

system/lib/libc/musl/include/alltypes.h.in

@@ -73,7 +73,14 @@ TYPEDEF struct __mbstate_t { unsigned __opaque1, __opaque2; } mbstate_t;
 
 TYPEDEF struct __locale_struct * locale_t;
 
-TYPEDEF struct __sigset_t { unsigned long __bits[128/sizeof(long)]; } sigset_t;
+// Musl uses 128 bytes for sigset_t, presumably for some kind of ABI
+// compatability with the kernel or GLIBC, but in emscripten we can be precise.
+// Since we have _NSIG = 65 which only need 2 `long`s for the bitmask.
+// The signals we support are
+// 1 - 31 - standard POSIX signals (see emscripten/bits/signal.h)
+// 32 - 34 - pthread-specific signals (see pthread_impl.h>
+// 35 - 65 - user-defined RT signals (we don't currently have any test coverage of these).
+TYPEDEF struct __sigset_t { unsigned long __bits[2]; } sigset_t;
 
 STRUCT iovec { void *iov_base; size_t iov_len; };
 

test/codesize/test_codesize_cxx_lto.json

@@ -2,9 +2,9 @@
   "a.out.js": 18563,
   "a.out.js.gz": 7666,
   "a.out.nodebug.wasm": 101956,
-  "a.out.nodebug.wasm.gz": 39461,
+  "a.out.nodebug.wasm.gz": 39460,
   "total": 120519,
-  "total_gz": 47127,
+  "total_gz": 47126,
   "sent": [
     "a (emscripten_resize_heap)",
     "b (_setitimer_js)",

test/codesize/test_codesize_hello_dylink_all.json

@@ -1,7 +1,7 @@
 {
   "a.out.js": 244300,
-  "a.out.nodebug.wasm": 577451,
-  "total": 821751,
+  "a.out.nodebug.wasm": 577444,
+  "total": 821744,
   "sent": [
     "IMG_Init",
     "IMG_Load",

test/core/test_signals.c

@@ -146,6 +146,7 @@ void test_sigaction() {
 
 void test_sigemptyset() {
   sigset_t s = { 0 };
+  printf("sizeof sigset_t: %zu\n", sizeof(sigset_t));
   assert(sigisemptyset(&s));
   sigaddset(&s, SIGUSR1);
   assert(!sigisemptyset(&s));