diff --git a/system/lib/libc/README.md b/system/lib/libc/README.md
index e970933eb771a..8b4b6f8125186 100644
--- a/system/lib/libc/README.md
+++ b/system/lib/libc/README.md
@@ -7,8 +7,7 @@ and use a script (`system/lib/update_musl.py`) to pull in updates.
 
 Some changes have been made to the version that was taken from upstream, including:
 
- * Emscripten-specific changes (from before this readme existed). These should be marked with `XXX EMSCRIPTEN` in the source, or ifdefed with `#if __EMSCRIPTEN__`. They are mostly in pthreads code and hopefully temporary.
- * Backporting an operator-precedence warning fix from 6e76e1540fc58a418494bf5eb832b556f9c5763e in the upstream version.
+ * Emscripten-specific changes (from before this readme existed). These should be marked with `XXX EMSCRIPTEN` in the source, or ifdefed with `#ifdef __EMSCRIPTEN__`. They are mostly in pthreads code and hopefully temporary.
  * Switch to using the wasi `fd_write` syscall instead of `writev`.
  * Simplify stdout stream handling: do not support seeking, terminal handling, etc., as it just increases code size and Emscripten doesn't have those features anyhow.
  * Setting `_POSIX_REALTIME_SIGNALS` and `_POSIX_SPAWN` macros to -1, to exclude unsupported functions.
diff --git a/system/lib/libc/musl/arch/emscripten/bits/fenv.h b/system/lib/libc/musl/arch/emscripten/bits/fenv.h
index d3512cb6f7f53..96b60ee219548 100644
--- a/system/lib/libc/musl/arch/emscripten/bits/fenv.h
+++ b/system/lib/libc/musl/arch/emscripten/bits/fenv.h
@@ -6,22 +6,6 @@
 #define FE_TOWARDZERO 0xc00
 
 typedef unsigned short fexcept_t;
-
-typedef struct {
-	unsigned short __control_word;
-	unsigned short __unused1;
-	unsigned short __status_word;
-	unsigned short __unused2;
-	unsigned short __tags;
-	unsigned short __unused3;
-	unsigned int __eip;
-	unsigned short __cs_selector;
-	unsigned int __opcode:11;
-	unsigned int __unused4:5;
-	unsigned int __data_offset;
-	unsigned short __data_selector;
-	unsigned short __unused5;
-	unsigned int __mxcsr;
-} fenv_t;
+typedef unsigned short fenv_t;
 
 #define FE_DFL_ENV      ((const fenv_t *) -1)
diff --git a/system/lib/libc/musl/arch/emscripten/bits/limits.h b/system/lib/libc/musl/arch/emscripten/bits/limits.h
index 7a09fdc1d175d..b36e964152ea1 100644
--- a/system/lib/libc/musl/arch/emscripten/bits/limits.h
+++ b/system/lib/libc/musl/arch/emscripten/bits/limits.h
@@ -1 +1,3 @@
-#define PAGE_SIZE 65536
+// A value used historically in Emscripten, and which we don't have a strong
+// reason to change so far.
+#define PAGESIZE 65536
diff --git a/system/lib/libc/musl/arch/emscripten/bits/mman.h b/system/lib/libc/musl/arch/emscripten/bits/mman.h
new file mode 100644
index 0000000000000..c52e718d0623f
--- /dev/null
+++ b/system/lib/libc/musl/arch/emscripten/bits/mman.h
@@ -0,0 +1,4 @@
+// XXX Emscripten in sync with both:
+// - musl/arch/x86_64/bits/mman.h
+// - musl/arch/i386/bits/mman.h
+#define MAP_32BIT      0x40
diff --git a/system/lib/libc/musl/arch/emscripten/bits/posix.h b/system/lib/libc/musl/arch/emscripten/bits/posix.h
index 30a38714f36dd..0dd953c3223f5 100644
--- a/system/lib/libc/musl/arch/emscripten/bits/posix.h
+++ b/system/lib/libc/musl/arch/emscripten/bits/posix.h
@@ -1,2 +1,9 @@
+#ifdef __wasm64__
+// 64-bit wide pointers under wasm64
+#define _POSIX_V6_LP64_OFF64  1
+#define _POSIX_V7_LP64_OFF64  1
+#else
+// 32-bit wide pointers under wasm32
 #define _POSIX_V6_ILP32_OFFBIG  1
 #define _POSIX_V7_ILP32_OFFBIG  1
+#endif
diff --git a/system/lib/libc/musl/arch/emscripten/bits/setjmp.h b/system/lib/libc/musl/arch/emscripten/bits/setjmp.h
index decd26dca07a0..1c9aa40ed60c4 100644
--- a/system/lib/libc/musl/arch/emscripten/bits/setjmp.h
+++ b/system/lib/libc/musl/arch/emscripten/bits/setjmp.h
@@ -1 +1,2 @@
+// XXX Emscripten in sync with musl/arch/i386/bits/setjmp.h
 typedef unsigned long __jmp_buf[6];
diff --git a/system/lib/libc/musl/arch/emscripten/bits/signal.h b/system/lib/libc/musl/arch/emscripten/bits/signal.h
index 58bc5e2c3a780..0c989dfdb9ef9 100644
--- a/system/lib/libc/musl/arch/emscripten/bits/signal.h
+++ b/system/lib/libc/musl/arch/emscripten/bits/signal.h
@@ -1,3 +1,4 @@
+// XXX Emscripten in sync with musl/arch/i386/bits/signal.h
 #if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
  || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
 
@@ -7,25 +8,44 @@
 #endif
 
 #ifdef _GNU_SOURCE
-#define REG_GS          0
-#define REG_FS          1
-#define REG_ES          2
-#define REG_DS          3
-#define REG_EDI         4
-#define REG_ESI         5
-#define REG_EBP         6
-#define REG_ESP         7
-#define REG_EBX         8
-#define REG_EDX         9
-#define REG_ECX         10
-#define REG_EAX         11
-#define REG_TRAPNO      12
-#define REG_ERR         13
-#define REG_EIP         14
-#define REG_CS          15
-#define REG_EFL         16
-#define REG_UESP        17
-#define REG_SS          18
+enum { REG_GS = 0 };
+#define REG_GS REG_GS
+enum { REG_FS = 1 };
+#define REG_FS REG_FS
+enum { REG_ES = 2 };
+#define REG_ES REG_ES
+enum { REG_DS = 3 };
+#define REG_DS REG_DS
+enum { REG_EDI = 4 };
+#define REG_EDI REG_EDI
+enum { REG_ESI = 5 };
+#define REG_ESI REG_ESI
+enum { REG_EBP = 6 };
+#define REG_EBP REG_EBP
+enum { REG_ESP = 7 };
+#define REG_ESP REG_ESP
+enum { REG_EBX = 8 };
+#define REG_EBX REG_EBX
+enum { REG_EDX = 9 };
+#define REG_EDX REG_EDX
+enum { REG_ECX = 10 };
+#define REG_ECX REG_ECX
+enum { REG_EAX = 11 };
+#define REG_EAX REG_EAX
+enum { REG_TRAPNO = 12 };
+#define REG_TRAPNO REG_TRAPNO
+enum { REG_ERR = 13 };
+#define REG_ERR REG_ERR
+enum { REG_EIP = 14 };
+#define REG_EIP REG_EIP
+enum { REG_CS = 15 };
+#define REG_CS REG_CS
+enum { REG_EFL = 16 };
+#define REG_EFL REG_EFL
+enum { REG_UESP = 17 };
+#define REG_UESP REG_UESP
+enum { REG_SS = 18 };
+#define REG_SS REG_SS
 #endif
 
 struct sigaltstack {
diff --git a/system/lib/libc/musl/arch/emscripten/bits/stat.h b/system/lib/libc/musl/arch/emscripten/bits/stat.h
index bfa9a597bcf6d..d0259d1483089 100644
--- a/system/lib/libc/musl/arch/emscripten/bits/stat.h
+++ b/system/lib/libc/musl/arch/emscripten/bits/stat.h
@@ -1,8 +1,8 @@
+// XXX Emscripten in sync with musl/arch/i386/bits/stat.h except for the padding and 64-bit time_t redirections change.
+
 /* copied from kernel definition, but with padding replaced
  * by the corresponding correctly-sized userspace types. */
-
-struct stat
-{
+struct stat {
 	dev_t st_dev;
 #ifndef __EMSCRIPTEN__
 	int __st_dev_padding;
@@ -19,6 +19,12 @@ struct stat
 	off_t st_size;
 	blksize_t st_blksize;
 	blkcnt_t st_blocks;
+#ifndef __EMSCRIPTEN__ // XXX Emscripten no need to activate the symbol redirections for 64-bit time_t.
+	struct {
+		long tv_sec;
+		long tv_nsec;
+	} __st_atim32, __st_mtim32, __st_ctim32;
+#endif
 	struct timespec st_atim;
 	struct timespec st_mtim;
 	struct timespec st_ctim;
diff --git a/system/lib/libc/musl/arch/emscripten/bits/user.h b/system/lib/libc/musl/arch/emscripten/bits/user.h
index fa623621eeba3..e69de29bb2d1d 100644
--- a/system/lib/libc/musl/arch/emscripten/bits/user.h
+++ b/system/lib/libc/musl/arch/emscripten/bits/user.h
@@ -1,48 +0,0 @@
-#undef __WORDSIZE
-#define __WORDSIZE 32
-
-typedef struct user_fpregs_struct
-{
-	long cwd, swd, twd, fip, fcs, foo, fos, st_space[20];
-} elf_fpregset_t;
-
-typedef struct user_fpxregs_struct
-{
-	unsigned short cwd, swd, twd, fop;
-	long fip, fcs, foo, fos, mxcsr, reserved;
-	long st_space[32], xmm_space[32], padding[56];
-} elf_fpxregset_t;
-
-struct user_regs_struct
-{
-	long ebx, ecx, edx, esi, edi, ebp, eax, xds, xes, xfs, xgs;
-	long orig_eax, eip, xcs, eflags, esp, xss;
-};
-
-#define ELF_NGREG 17
-typedef unsigned long elf_greg_t, elf_gregset_t[ELF_NGREG];
-
-struct user
-{
-	struct user_regs_struct		regs;
-	int				u_fpvalid;
-	struct user_fpregs_struct	i387;
-	unsigned long			u_tsize;
-	unsigned long			u_dsize;
-	unsigned long			u_ssize;
-	unsigned long			start_code;
-	unsigned long			start_stack;
-	long				signal;
-	int				reserved;
-	struct user_regs_struct		*u_ar0;
-	struct user_fpregs_struct	*u_fpstate;
-	unsigned long			magic;
-	char				u_comm[32];
-	int				u_debugreg[8];
-};
-
-#define PAGE_MASK		(~(PAGE_SIZE-1))
-#define NBPG			PAGE_SIZE
-#define UPAGES			1
-#define HOST_TEXT_START_ADDR	(u.start_code)
-#define HOST_STACK_END_ADDR	(u.start_stack + u.u_ssize * NBPG)
diff --git a/system/lib/libc/musl/arch/generic/bits/ipc.h b/system/lib/libc/musl/arch/generic/bits/ipc.h
index 40d6f3a2587cf..779c42fd7bf52 100644
--- a/system/lib/libc/musl/arch/generic/bits/ipc.h
+++ b/system/lib/libc/musl/arch/generic/bits/ipc.h
@@ -9,3 +9,5 @@ struct ipc_perm {
 	long __pad1;
 	long __pad2;
 };
+
+#define IPC_64 0x100
diff --git a/system/lib/libc/musl/include/setjmp.h b/system/lib/libc/musl/include/setjmp.h
index af72c80cdbce0..5aabfa95c4a05 100644
--- a/system/lib/libc/musl/include/setjmp.h
+++ b/system/lib/libc/musl/include/setjmp.h
@@ -26,7 +26,7 @@ typedef struct __jmp_buf_tag {
  || defined(_BSD_SOURCE)
 typedef jmp_buf sigjmp_buf;
 /* XXX EMSCRIPTEN: No signals support, alias sigsetjmp and siglongjmp to their non-signals counterparts. */
-#if __EMSCRIPTEN__ && !defined(LLVM_LIBC)
+#if defined(__EMSCRIPTEN__) && !defined(LLVM_LIBC)
 #define sigsetjmp(buf, x) setjmp((buf))
 #define siglongjmp(buf, val) longjmp(buf, val)
 #else
diff --git a/system/lib/libc/musl/include/unistd.h b/system/lib/libc/musl/include/unistd.h
index d98a7460db4d3..d194bf1243c46 100644
--- a/system/lib/libc/musl/include/unistd.h
+++ b/system/lib/libc/musl/include/unistd.h
@@ -240,20 +240,20 @@ pid_t gettid(void);
 #define _POSIX_NO_TRUNC         1
 #define _POSIX_RAW_SOCKETS      _POSIX_VERSION
 
-#ifndef __EMSCRIPTEN__
-#define _POSIX_REALTIME_SIGNALS _POSIX_VERSION
-#else
+#ifdef __EMSCRIPTEN__
 #define _POSIX_REALTIME_SIGNALS -1
+#else
+#define _POSIX_REALTIME_SIGNALS _POSIX_VERSION
 #endif
 
 #define _POSIX_REGEXP           1
 #define _POSIX_SAVED_IDS        1
 #define _POSIX_SHELL            1
 
-#ifndef __EMSCRIPTEN__
-#define _POSIX_SPAWN            _POSIX_VERSION
-#else
+#ifdef __EMSCRIPTEN__
 #define _POSIX_SPAWN            -1
+#else
+#define _POSIX_SPAWN            _POSIX_VERSION
 #endif
 
 #define _POSIX_VDISABLE         0
@@ -263,10 +263,10 @@ pid_t gettid(void);
 #else
 #define _POSIX_THREADS          _POSIX_VERSION
 #endif
-#ifndef __EMSCRIPTEN__
-#define _POSIX_THREAD_PROCESS_SHARED _POSIX_VERSION
-#else
+#ifdef __EMSCRIPTEN__
 #define _POSIX_THREAD_PROCESS_SHARED -1
+#else
+#define _POSIX_THREAD_PROCESS_SHARED _POSIX_VERSION
 #endif
 #define _POSIX_THREAD_SAFE_FUNCTIONS _POSIX_VERSION
 #define _POSIX_THREAD_ATTR_STACKADDR _POSIX_VERSION
diff --git a/system/lib/libc/musl/src/exit/abort.c b/system/lib/libc/musl/src/exit/abort.c
index a6427d51d66e9..8ff8a8626ee07 100644
--- a/system/lib/libc/musl/src/exit/abort.c
+++ b/system/lib/libc/musl/src/exit/abort.c
@@ -6,13 +6,13 @@
 #include "lock.h"
 #include "ksigaction.h"
 
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 #include "emscripten_internal.h"
 #endif
 
 _Noreturn void abort(void)
 {
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 	/* In emscripten we call out to JS to perform the actual abort where it can
 	 * produce a nice error.
 	 * Note that the JS library function is not called `abort` to avoid conflict
diff --git a/system/lib/libc/musl/src/internal/libm.h b/system/lib/libc/musl/src/internal/libm.h
index a47208aa6ad3c..9d8b892d5b3e8 100644
--- a/system/lib/libc/musl/src/internal/libm.h
+++ b/system/lib/libc/musl/src/internal/libm.h
@@ -144,6 +144,16 @@ static inline long double fp_barrierl(long double x)
 }
 #endif
 
+#ifdef __EMSCRIPTEN__
+/*
+ * wasm doesn't have user-accessible floating point exceptions, so there's
+ * no point in trying to force expression evaluations to produce them.
+ */
+#define fp_force_evalf(x)
+#define fp_force_eval(x)
+#define fp_force_evall(x)
+#define FORCE_EVAL(x)
+#else
 /* fp_force_eval ensures that the input value is computed when that's
    otherwise unused.  To prevent the constant folding of the input
    expression, an additional fp_barrier may be needed or a compilation
@@ -177,13 +187,6 @@ static inline void fp_force_evall(long double x)
 }
 #endif
 
-#ifdef __EMSCRIPTEN__
-/*
- * asm.js doesn't have user-accessible floating point exceptions, so there's
- * no point in trying to force expression evaluations to produce them.
- */
-#define FORCE_EVAL(x)
-#else
 #define FORCE_EVAL(x) do {                        \
 	if (sizeof(x) == sizeof(float)) {         \
 		fp_force_evalf(x);                \
diff --git a/system/lib/libc/musl/src/internal/locale_impl.h b/system/lib/libc/musl/src/internal/locale_impl.h
index 9a7b07c4aac0e..1f46f88fa7d74 100644
--- a/system/lib/libc/musl/src/internal/locale_impl.h
+++ b/system/lib/libc/musl/src/internal/locale_impl.h
@@ -31,7 +31,7 @@ hidden char *__gettextdomain(void);
 
 #define LOC_MAP_FAILED ((const struct __locale_map *)-1)
 
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 // Disable message translation completely under emscripten since we don't
 // support loading any actual locale data, and even looking up the current
 // local via CURRENT_LOCALE via TLS is not free.
diff --git a/system/lib/libc/musl/src/internal/pthread_impl.h b/system/lib/libc/musl/src/internal/pthread_impl.h
index a366b6cef8eb3..d7978ba8fccf7 100644
--- a/system/lib/libc/musl/src/internal/pthread_impl.h
+++ b/system/lib/libc/musl/src/internal/pthread_impl.h
@@ -237,7 +237,7 @@ static inline void __wake(volatile void *addr, int cnt, int priv)
 	if (priv) priv = FUTEX_PRIVATE;
 	if (cnt<0) cnt = INT_MAX;
 #ifdef __EMSCRIPTEN__
-	emscripten_futex_wake(addr, (cnt)<0?INT_MAX:(cnt));
+	emscripten_futex_wake(addr, cnt);
 #else
 	__syscall(SYS_futex, addr, FUTEX_WAKE|priv, cnt) != -ENOSYS ||
 	__syscall(SYS_futex, addr, FUTEX_WAKE, cnt);
diff --git a/system/lib/libc/musl/src/internal/syscall.h b/system/lib/libc/musl/src/internal/syscall.h
index 1a6c4313852d7..b4152b6145eff 100644
--- a/system/lib/libc/musl/src/internal/syscall.h
+++ b/system/lib/libc/musl/src/internal/syscall.h
@@ -30,7 +30,7 @@
 typedef long syscall_arg_t;
 #endif
 
-#ifdef __cplusplus
+#ifdef __cplusplus // XXX Emscripten we need C linkage for this
 extern "C" {
 #endif
 hidden long __syscall_ret(unsigned long),
@@ -40,14 +40,7 @@ hidden long __syscall_ret(unsigned long),
 }
 #endif
 
-#ifndef __EMSCRIPTEN__
-#define __syscall1(n,a) __syscall1(n,__scc(a))
-#define __syscall2(n,a,b) __syscall2(n,__scc(a),__scc(b))
-#define __syscall3(n,a,b,c) __syscall3(n,__scc(a),__scc(b),__scc(c))
-#define __syscall4(n,a,b,c,d) __syscall4(n,__scc(a),__scc(b),__scc(c),__scc(d))
-#define __syscall5(n,a,b,c,d,e) __syscall5(n,__scc(a),__scc(b),__scc(c),__scc(d),__scc(e))
-#define __syscall6(n,a,b,c,d,e,f) __syscall6(n,__scc(a),__scc(b),__scc(c),__scc(d),__scc(e),__scc(f))
-#else // __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 #define __syscall_emscripten(n, ...) n(__VA_ARGS__)
 #define __syscall_emscripten0(n) __syscall_emscripten(n)
 #define __syscall_emscripten1(n,a) __syscall_emscripten(n,__scc(a))
@@ -56,7 +49,14 @@ hidden long __syscall_ret(unsigned long),
 #define __syscall_emscripten4(n,a,b,c,d) __syscall_emscripten(n,__scc(a),__scc(b),__scc(c),__scc(d))
 #define __syscall_emscripten5(n,a,b,c,d,e) __syscall_emscripten(n,__scc(a),__scc(b),__scc(c),__scc(d),__scc(e))
 #define __syscall_emscripten6(n,a,b,c,d,e,f) __syscall_emscripten(n,__scc(a),__scc(b),__scc(c),__scc(d),__scc(e),__scc(f))
-#endif // __EMSCRIPTEN__
+#else // !defined(__EMSCRIPTEN__)
+#define __syscall1(n,a) __syscall1(n,__scc(a))
+#define __syscall2(n,a,b) __syscall2(n,__scc(a),__scc(b))
+#define __syscall3(n,a,b,c) __syscall3(n,__scc(a),__scc(b),__scc(c))
+#define __syscall4(n,a,b,c,d) __syscall4(n,__scc(a),__scc(b),__scc(c),__scc(d))
+#define __syscall5(n,a,b,c,d,e) __syscall5(n,__scc(a),__scc(b),__scc(c),__scc(d),__scc(e))
+#define __syscall6(n,a,b,c,d,e,f) __syscall6(n,__scc(a),__scc(b),__scc(c),__scc(d),__scc(e),__scc(f))
+#endif // !defined(__EMSCRIPTEN__)
 
 #define __SYSCALL_NARGS_X(a,b,c,d,e,f,g,h,n,...) n
 #define __SYSCALL_NARGS(...) __SYSCALL_NARGS_X(__VA_ARGS__,7,6,5,4,3,2,1,0,)
@@ -64,10 +64,10 @@ hidden long __syscall_ret(unsigned long),
 #define __SYSCALL_CONCAT(a,b) __SYSCALL_CONCAT_X(a,b)
 #define __SYSCALL_DISP(b,...) __SYSCALL_CONCAT(b,__SYSCALL_NARGS(__VA_ARGS__))(__VA_ARGS__)
 
-#ifndef __EMSCRIPTEN__
-#define __syscall(...) __SYSCALL_DISP(__syscall,__VA_ARGS__)
-#else
+#ifdef __EMSCRIPTEN__
 #define __syscall(...) __SYSCALL_DISP(__syscall_emscripten,__VA_ARGS__)
+#else
+#define __syscall(...) __SYSCALL_DISP(__syscall,__VA_ARGS__)
 #endif
 
 #define syscall(...) __syscall_ret(__syscall(__VA_ARGS__))
@@ -75,7 +75,9 @@ hidden long __syscall_ret(unsigned long),
 #define socketcall(nm,a,b,c,d,e,f) __syscall_ret(__socketcall(nm,a,b,c,d,e,f))
 #define socketcall_cp(nm,a,b,c,d,e,f) __syscall_ret(__socketcall_cp(nm,a,b,c,d,e,f))
 
-#ifndef __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
+#define __syscall_cp(...) __syscall(__VA_ARGS__)
+#else // !defined(__EMSCRIPTEN__)
 #define __syscall_cp0(n) (__syscall_cp)(n,0,0,0,0,0,0)
 #define __syscall_cp1(n,a) (__syscall_cp)(n,__scc(a),0,0,0,0,0)
 #define __syscall_cp2(n,a,b) (__syscall_cp)(n,__scc(a),__scc(b),0,0,0,0)
@@ -85,9 +87,7 @@ hidden long __syscall_ret(unsigned long),
 #define __syscall_cp6(n,a,b,c,d,e,f) (__syscall_cp)(n,__scc(a),__scc(b),__scc(c),__scc(d),__scc(e),__scc(f))
 
 #define __syscall_cp(...) __SYSCALL_DISP(__syscall_cp,__VA_ARGS__)
-#else // __EMSCRIPTEN__
-#define __syscall_cp(...) __syscall(__VA_ARGS__)
-#endif // __EMSCRIPTEN__
+#endif // !defined(__EMSCRIPTEN__)
 
 #define syscall_cp(...) __syscall_ret(__syscall_cp(__VA_ARGS__))
 
@@ -408,7 +408,12 @@ hidden long __syscall_ret(unsigned long),
 #define SIOCGSTAMPNS_OLD 0x8907
 #endif
 
-#ifndef __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
+#define __sys_open2(x,pn,fl) __syscall_openat(__scc(AT_FDCWD), __scc(pn), __scc((fl)|O_LARGEFILE))
+#define __sys_open3(x,pn,fl,mo) __syscall_openat(__scc(AT_FDCWD), __scc(pn), __scc((fl)|O_LARGEFILE), __scc(mo))
+#define __sys_open_cp2(x,pn,fl) __syscall_openat(__scc(AT_FDCWD), __scc(pn), __scc((fl)|O_LARGEFILE))
+#define __sys_open_cp3(x,pn,fl,mo) __syscall_openat(__scc(AT_FDCWD), __scc(pn), __scc((fl)|O_LARGEFILE), __scc(mo))
+#else // !defined(__EMSCRIPTEN__)
 #ifdef SYS_open
 #define __sys_open2(x,pn,fl) __syscall2(SYS_open, pn, (fl)|O_LARGEFILE)
 #define __sys_open3(x,pn,fl,mo) __syscall3(SYS_open, pn, (fl)|O_LARGEFILE, mo)
@@ -420,13 +425,7 @@ hidden long __syscall_ret(unsigned long),
 #define __sys_open_cp2(x,pn,fl) __syscall_cp3(SYS_openat, AT_FDCWD, pn, (fl)|O_LARGEFILE)
 #define __sys_open_cp3(x,pn,fl,mo) __syscall_cp4(SYS_openat, AT_FDCWD, pn, (fl)|O_LARGEFILE, mo)
 #endif
-#else // __EMSCRIPTEN__
-#define __sys_open2(x,pn,fl) __syscall_openat(__scc(AT_FDCWD), __scc(pn), __scc((fl)|O_LARGEFILE))
-#define __sys_open3(x,pn,fl,mo) __syscall_openat(__scc(AT_FDCWD), __scc(pn), __scc((fl)|O_LARGEFILE), __scc(mo))
-#define __sys_open_cp2(x,pn,fl) __syscall_openat(__scc(AT_FDCWD), __scc(pn), __scc((fl)|O_LARGEFILE))
-#define __sys_open_cp3(x,pn,fl,mo) __syscall_openat(__scc(AT_FDCWD), __scc(pn), __scc((fl)|O_LARGEFILE), __scc(mo))
-#endif
-
+#endif // !defined(__EMSCRIPTEN__)
 #define __sys_open(...) __SYSCALL_DISP(__sys_open,,__VA_ARGS__)
 #define sys_open(...) __syscall_ret(__sys_open(__VA_ARGS__))
 
@@ -445,7 +444,7 @@ hidden long __emulate_wait4(int, int *, int, void *, int);
 #define sys_wait4(a,b,c,d) __syscall_ret(__sys_wait4(a,b,c,d))
 #define sys_wait4_cp(a,b,c,d) __syscall_ret(__sys_wait4_cp(a,b,c,d))
 
-#ifdef __cplusplus
+#ifdef __cplusplus // XXX Emscripten static array size is a C99 feature, not permitted in C++
 hidden void __procfdname(char __buf[], unsigned);
 #else
 hidden void __procfdname(char __buf[static 15+3*sizeof(int)], unsigned);
diff --git a/system/lib/libc/musl/src/linux/sbrk.c b/system/lib/libc/musl/src/linux/sbrk.c
index 8e3a9b6645d68..cf483a57fb329 100644
--- a/system/lib/libc/musl/src/linux/sbrk.c
+++ b/system/lib/libc/musl/src/linux/sbrk.c
@@ -1,4 +1,4 @@
-#if !__EMSCRIPTEN__ /* Emscripten controls sbrk itself */
+#ifndef __EMSCRIPTEN__ /* Emscripten controls sbrk itself */
 #define _BSD_SOURCE
 #include <unistd.h>
 #include <stdint.h>
@@ -11,4 +11,3 @@ void *sbrk(intptr_t inc)
 	return (void *)__syscall(SYS_brk, 0);
 }
 #endif
-
diff --git a/system/lib/libc/musl/src/math/sqrt.c b/system/lib/libc/musl/src/math/sqrt.c
index 6854c98381642..3b07abee8380a 100644
--- a/system/lib/libc/musl/src/math/sqrt.c
+++ b/system/lib/libc/musl/src/math/sqrt.c
@@ -27,7 +27,7 @@ double sqrt(double x)
 {
 // XXX EMSCRIPTEN: use the wasm instruction via clang builtin
 // See https://github.com/emscripten-core/emscripten/issues/9236
-#ifdef __wasm__
+#ifdef __EMSCRIPTEN__
 	return __builtin_sqrt(x);
 #else
 	uint64_t ix, top, m;
diff --git a/system/lib/libc/musl/src/math/sqrtf.c b/system/lib/libc/musl/src/math/sqrtf.c
index fd74702691215..d1f3b9595ccd0 100644
--- a/system/lib/libc/musl/src/math/sqrtf.c
+++ b/system/lib/libc/musl/src/math/sqrtf.c
@@ -18,7 +18,7 @@ float sqrtf(float x)
 {
 // XXX EMSCRIPTEN: use the wasm instruction via clang builtin
 // See https://github.com/emscripten-core/emscripten/issues/9236
-#ifdef __wasm__
+#ifdef __EMSCRIPTEN__
 	return __builtin_sqrtf(x);
 #else
 	uint32_t ix, m, m1, m0, even, ey;
diff --git a/system/lib/libc/musl/src/network/freeaddrinfo.c b/system/lib/libc/musl/src/network/freeaddrinfo.c
index c4016d9f7c246..68fdc09cb9e10 100644
--- a/system/lib/libc/musl/src/network/freeaddrinfo.c
+++ b/system/lib/libc/musl/src/network/freeaddrinfo.c
@@ -6,7 +6,7 @@
 
 void freeaddrinfo(struct addrinfo *p)
 {
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 	// Emscripten's usage of this structure is very simple: we always allocate
 	// ai_addr, and do not use the linked list aspect at all. There is also no
 	// aliasing with aibuf.
diff --git a/system/lib/libc/musl/src/sched/sched_yield.c b/system/lib/libc/musl/src/sched/sched_yield.c
index 7bd3846fc239e..82a14a3914e95 100644
--- a/system/lib/libc/musl/src/sched/sched_yield.c
+++ b/system/lib/libc/musl/src/sched/sched_yield.c
@@ -1,7 +1,7 @@
 #include <sched.h>
 #include "syscall.h"
 
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 #include <emscripten/emscripten.h>
 #include <emscripten/threading.h>
 #include "threading_internal.h"
@@ -9,7 +9,7 @@
 
 int sched_yield()
 {
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 	// SharedArrayBuffer and wasm threads do not support explicit yielding.
 	// For now we at least call `emscripten_yield` which processes the event queue
 	// (along with other essential tasks).
diff --git a/system/lib/libc/musl/src/stat/fchmod.c b/system/lib/libc/musl/src/stat/fchmod.c
index 58badd5c01bb8..ca2a6c783b2bd 100644
--- a/system/lib/libc/musl/src/stat/fchmod.c
+++ b/system/lib/libc/musl/src/stat/fchmod.c
@@ -9,7 +9,7 @@
 int fchmod(int fd, mode_t mode)
 {
 	int ret = __syscall(SYS_fchmod, fd, mode);
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 	if (ret != -EBADF || !__wasi_fd_is_valid(fd))
 		return __syscall_ret(ret);
 #else
diff --git a/system/lib/libc/musl/src/stat/fstatat.c b/system/lib/libc/musl/src/stat/fstatat.c
index 631451268c590..6d499c44174a3 100644
--- a/system/lib/libc/musl/src/stat/fstatat.c
+++ b/system/lib/libc/musl/src/stat/fstatat.c
@@ -145,7 +145,7 @@ static int fstatat_kstat(int fd, const char *restrict path, struct stat *restric
 int __fstatat(int fd, const char *restrict path, struct stat *restrict st, int flag)
 {
 	int ret;
-#ifdef __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__ // XXX Emscripten statx syscall unsupported
 	// some logic here copied from fstatat_kstat above
 	if (flag==AT_EMPTY_PATH && fd>=0 && !*path)
 		ret = __syscall(SYS_fstat, fd, st);
diff --git a/system/lib/libc/musl/src/stdio/__stdio_read.c b/system/lib/libc/musl/src/stdio/__stdio_read.c
index 392a4858281f3..c7adefe079f01 100644
--- a/system/lib/libc/musl/src/stdio/__stdio_read.c
+++ b/system/lib/libc/musl/src/stdio/__stdio_read.c
@@ -8,8 +8,7 @@ size_t __stdio_read(FILE *f, unsigned char *buf, size_t len)
 		{ .iov_base = f->buf, .iov_len = f->buf_size }
 	};
 	ssize_t cnt;
-
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 	size_t num;
 	if (__wasi_syscall_ret(__wasi_fd_read(f->fd, (struct __wasi_iovec_t*)iov, 2, &num))) {
 		num = -1;
diff --git a/system/lib/libc/musl/src/stdio/__stdio_write.c b/system/lib/libc/musl/src/stdio/__stdio_write.c
index cce9f6a16a558..097acd53b79cc 100644
--- a/system/lib/libc/musl/src/stdio/__stdio_write.c
+++ b/system/lib/libc/musl/src/stdio/__stdio_write.c
@@ -12,7 +12,7 @@ size_t __stdio_write(FILE *f, const unsigned char *buf, size_t len)
 	int iovcnt = 2;
 	ssize_t cnt;
 	for (;;) {
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 		size_t num;
 		if (__wasi_syscall_ret(__wasi_fd_write(f->fd, (struct __wasi_ciovec_t*)iov, iovcnt, &num))) {
 			num = -1;
diff --git a/system/lib/libc/musl/src/stdio/stdout.c b/system/lib/libc/musl/src/stdio/stdout.c
index 62cf40220a5c4..5054e5b6ccc14 100644
--- a/system/lib/libc/musl/src/stdio/stdout.c
+++ b/system/lib/libc/musl/src/stdio/stdout.c
@@ -1,6 +1,6 @@
 #include "stdio_impl.h"
 
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 // Emscripten doesn't support terminal seeking.
 static off_t __emscripten_stdout_seek(FILE *f, off_t off, int whence)
 {
@@ -23,7 +23,7 @@ hidden FILE __stdout_FILE = {
 	.fd = 1,
 	.flags = F_PERM | F_NORD,
 	.lbf = '\n',
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 	// avoid stout_write which adds special terminal window size handling, which emscripten doesn't support anyhow
 	.write = __stdio_write,
 	.seek = __emscripten_stdout_seek,
diff --git a/system/lib/libc/musl/src/stdio/vfprintf.c b/system/lib/libc/musl/src/stdio/vfprintf.c
index c0542b599024c..ce1acf9140e48 100644
--- a/system/lib/libc/musl/src/stdio/vfprintf.c
+++ b/system/lib/libc/musl/src/stdio/vfprintf.c
@@ -147,7 +147,7 @@ typedef void (*pop_arg_long_double_t)(union arg *arg, va_list *ap);
 
 static void pop_arg_long_double(union arg *arg, va_list *ap)
 {
-  arg->f = va_arg(*ap, long double);
+	arg->f = va_arg(*ap, long double);
 }
 
 static void pop_arg(union arg *arg, int type, va_list *ap, pop_arg_long_double_t pop_arg_long_double)
diff --git a/system/lib/libc/musl/src/string/memcmp.c b/system/lib/libc/musl/src/string/memcmp.c
index c93cf8cc97330..ba9ab6d41d3c9 100644
--- a/system/lib/libc/musl/src/string/memcmp.c
+++ b/system/lib/libc/musl/src/string/memcmp.c
@@ -1,4 +1,4 @@
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 #include <stdint.h>
 #endif
 #include <string.h>
diff --git a/system/lib/libc/musl/src/thread/__timedwait.c b/system/lib/libc/musl/src/thread/__timedwait.c
index 9e3ccc9849257..51afba0044942 100644
--- a/system/lib/libc/musl/src/thread/__timedwait.c
+++ b/system/lib/libc/musl/src/thread/__timedwait.c
@@ -32,10 +32,10 @@ static int __futex4_cp(volatile void *addr, int op, int val, const struct timesp
 	if (r != -ENOSYS) return r;
 	return __syscall_cp(SYS_futex, addr, op & ~FUTEX_PRIVATE, val, to);
 }
-#endif
 
 static volatile int dummy = 0;
 weak_alias(dummy, __eintr_valid_flag);
+#endif
 
 int __timedwait_cp(volatile int *addr, int val,
 	clockid_t clk, const struct timespec *at, int priv)
@@ -64,11 +64,13 @@ int __timedwait_cp(volatile int *addr, int val,
 	r = -__futex4_cp(addr, FUTEX_WAIT|priv, val, top);
 #endif
 	if (r != EINTR && r != ETIMEDOUT && r != ECANCELED) r = 0;
+#ifndef __EMSCRIPTEN__ // XXX Emscripten revert musl commit a63c0104e496f7ba78b64be3cd299b41e8cd427f
 	/* Mitigate bug in old kernels wrongly reporting EINTR for non-
 	 * interrupting (SA_RESTART) signal handlers. This is only practical
 	 * when NO interrupting signal handlers have been installed, and
 	 * works by sigaction tracking whether that's the case. */
 	if (r == EINTR && !__eintr_valid_flag) r = 0;
+#endif
 
 	return r;
 }
diff --git a/system/lib/libc/musl/src/thread/pthread_mutex_timedlock.c b/system/lib/libc/musl/src/thread/pthread_mutex_timedlock.c
index 232c9b321a8e2..95eefb45ea0a8 100644
--- a/system/lib/libc/musl/src/thread/pthread_mutex_timedlock.c
+++ b/system/lib/libc/musl/src/thread/pthread_mutex_timedlock.c
@@ -77,7 +77,7 @@ int __pthread_mutex_timedlock(pthread_mutex_t *restrict m, const struct timespec
 #ifndef __EMSCRIPTEN__
 	if (type&8) return pthread_mutex_timedlock_pi(m, at);
 #endif
-	
+
 	int spins = 100;
 	while (spins-- && m->_m_lock && !m->_m_waiters) a_spin();
 
diff --git a/system/lib/libc/musl/src/time/clock_gettime.c b/system/lib/libc/musl/src/time/clock_gettime.c
index 18926de8ce8f3..36d901e85dff1 100644
--- a/system/lib/libc/musl/src/time/clock_gettime.c
+++ b/system/lib/libc/musl/src/time/clock_gettime.c
@@ -56,7 +56,7 @@ static void *volatile vdso_func = (void *)cgt_init;
 
 #endif
 
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 _Static_assert(CLOCK_REALTIME == __WASI_CLOCKID_REALTIME, "monotonic clock must match");
 _Static_assert(CLOCK_MONOTONIC == __WASI_CLOCKID_MONOTONIC, "monotonic clock must match");
 
diff --git a/system/lib/libc/musl/src/time/clock_nanosleep.c b/system/lib/libc/musl/src/time/clock_nanosleep.c
index 7ad2aba1a0b7a..3684e43aa14c6 100644
--- a/system/lib/libc/musl/src/time/clock_nanosleep.c
+++ b/system/lib/libc/musl/src/time/clock_nanosleep.c
@@ -1,7 +1,7 @@
 #include <time.h>
 #include <errno.h>
 #include "syscall.h"
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 #include <errno.h>
 #include <emscripten/threading.h>
 #endif
@@ -12,7 +12,7 @@
 int __clock_nanosleep(clockid_t clk, int flags, const struct timespec *req, struct timespec *rem)
 {
 	if (clk == CLOCK_THREAD_CPUTIME_ID) return EINVAL;
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 	if (!req || req->tv_nsec < 0 || req->tv_nsec > 999999999L || req->tv_sec < 0) {
 		return EINVAL;
 	}
diff --git a/system/lib/libc/musl/src/time/clock_settime.c b/system/lib/libc/musl/src/time/clock_settime.c
index ed0182fff664c..686488414371a 100644
--- a/system/lib/libc/musl/src/time/clock_settime.c
+++ b/system/lib/libc/musl/src/time/clock_settime.c
@@ -1,9 +1,6 @@
 #include <time.h>
 #include <errno.h>
 #include "syscall.h"
-#ifdef __EMSCRIPTEN__
-#include <errno.h>
-#endif
 
 #define IS32BIT(x) !((x)+0x80000000ULL>>32)
 
@@ -13,8 +10,7 @@ int clock_settime(clockid_t clk, const struct timespec *ts)
 	// JS and wasm VMs do not allow setting the time.
 	errno = EPERM;
 	return -1;
-#else
-#ifdef SYS_clock_settime64
+#elif defined(SYS_clock_settime64) // XXX EMSCRIPTEN replace #ifdef SYS_clock_settime64
 	time_t s = ts->tv_sec;
 	long ns = ts->tv_nsec;
 	int r = -ENOSYS;
@@ -29,5 +25,4 @@ int clock_settime(clockid_t clk, const struct timespec *ts)
 #else
 	return syscall(SYS_clock_settime, clk, ts);
 #endif
-#endif
 }
diff --git a/system/lib/libc/musl/src/unistd/fchdir.c b/system/lib/libc/musl/src/unistd/fchdir.c
index bcbd0fc9cc9cd..a22f5f4fed65d 100644
--- a/system/lib/libc/musl/src/unistd/fchdir.c
+++ b/system/lib/libc/musl/src/unistd/fchdir.c
@@ -9,7 +9,7 @@
 int fchdir(int fd)
 {
 	int ret = __syscall(SYS_fchdir, fd);
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 	if (ret != -EBADF || !__wasi_fd_is_valid(fd))
 		return __syscall_ret(ret);
 #else
diff --git a/system/lib/libc/musl/src/unistd/fchown.c b/system/lib/libc/musl/src/unistd/fchown.c
index a328189505444..02facc410b5d1 100644
--- a/system/lib/libc/musl/src/unistd/fchown.c
+++ b/system/lib/libc/musl/src/unistd/fchown.c
@@ -9,7 +9,7 @@
 int fchown(int fd, uid_t uid, gid_t gid)
 {
 	int ret = __syscall(SYS_fchown, fd, uid, gid);
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 	// We can't continue onwards to try the /proc/fd/NNN approach that musl does,
 	// as we don't support that much of POSIX.
 	return __syscall_ret(ret);
@@ -24,5 +24,5 @@ int fchown(int fd, uid_t uid, gid_t gid)
 #else
 	return syscall(SYS_fchownat, AT_FDCWD, buf, uid, gid, 0);
 #endif
-#endif // EMSCRIPTEN
+#endif // __EMSCRIPTEN__
 }
diff --git a/system/lib/libc/musl/src/unistd/fsync.c b/system/lib/libc/musl/src/unistd/fsync.c
index 2b26be534e96c..8c6c1d13dcc5d 100644
--- a/system/lib/libc/musl/src/unistd/fsync.c
+++ b/system/lib/libc/musl/src/unistd/fsync.c
@@ -3,7 +3,7 @@
 
 int fsync(int fd)
 {
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 	return __wasi_syscall_ret(__wasi_fd_sync(fd));
 #else
 	return syscall_cp(SYS_fsync, fd);
diff --git a/system/lib/libc/musl/src/unistd/pread.c b/system/lib/libc/musl/src/unistd/pread.c
index a2361a0473b51..7b790d47d1abc 100644
--- a/system/lib/libc/musl/src/unistd/pread.c
+++ b/system/lib/libc/musl/src/unistd/pread.c
@@ -3,7 +3,7 @@
 
 ssize_t pread(int fd, void *buf, size_t size, off_t ofs)
 {
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 	__wasi_iovec_t iov = {
 		.buf = buf,
 		.buf_len = size
diff --git a/system/lib/libc/musl/src/unistd/preadv.c b/system/lib/libc/musl/src/unistd/preadv.c
index fa6b78c101b3f..5c86d09cf2c7d 100644
--- a/system/lib/libc/musl/src/unistd/preadv.c
+++ b/system/lib/libc/musl/src/unistd/preadv.c
@@ -5,7 +5,7 @@
 
 ssize_t preadv(int fd, const struct iovec *iov, int count, off_t ofs)
 {
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 	size_t num;
 	if (__wasi_syscall_ret(__wasi_fd_pread(fd, (struct __wasi_iovec_t*)iov, count, ofs, &num))) {
 		return -1;
diff --git a/system/lib/libc/musl/src/unistd/pwrite.c b/system/lib/libc/musl/src/unistd/pwrite.c
index 3573ab3902f82..671d7732abd1a 100644
--- a/system/lib/libc/musl/src/unistd/pwrite.c
+++ b/system/lib/libc/musl/src/unistd/pwrite.c
@@ -3,7 +3,7 @@
 
 ssize_t pwrite(int fd, const void *buf, size_t size, off_t ofs)
 {
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 	__wasi_ciovec_t iov = {
 		.buf = buf,
 		.buf_len = size
diff --git a/system/lib/libc/musl/src/unistd/pwritev.c b/system/lib/libc/musl/src/unistd/pwritev.c
index bb44236c51ef7..b2d9d7c541f23 100644
--- a/system/lib/libc/musl/src/unistd/pwritev.c
+++ b/system/lib/libc/musl/src/unistd/pwritev.c
@@ -5,7 +5,7 @@
 
 ssize_t pwritev(int fd, const struct iovec *iov, int count, off_t ofs)
 {
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 	size_t num;
 	if (__wasi_syscall_ret(__wasi_fd_pwrite(fd, (struct __wasi_ciovec_t*)iov, count, ofs, &num))) {
 		return -1;
diff --git a/system/lib/libc/musl/src/unistd/read.c b/system/lib/libc/musl/src/unistd/read.c
index f079439c9d302..f84e9436c7c8b 100644
--- a/system/lib/libc/musl/src/unistd/read.c
+++ b/system/lib/libc/musl/src/unistd/read.c
@@ -3,7 +3,7 @@
 
 ssize_t read(int fd, void *buf, size_t count)
 {
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 	__wasi_iovec_t iov = {
 		.buf = buf,
 		.buf_len = count
diff --git a/system/lib/libc/musl/src/unistd/readv.c b/system/lib/libc/musl/src/unistd/readv.c
index bb0760da6e147..3a40c1e9626f6 100644
--- a/system/lib/libc/musl/src/unistd/readv.c
+++ b/system/lib/libc/musl/src/unistd/readv.c
@@ -3,7 +3,7 @@
 
 ssize_t readv(int fd, const struct iovec *iov, int count)
 {
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 	size_t num;
 	if (__wasi_syscall_ret(__wasi_fd_read(fd, (struct __wasi_iovec_t*)iov, count, &num))) {
 		num = -1;
diff --git a/system/lib/libc/musl/src/unistd/write.c b/system/lib/libc/musl/src/unistd/write.c
index 53742cd4fd972..135229be89121 100644
--- a/system/lib/libc/musl/src/unistd/write.c
+++ b/system/lib/libc/musl/src/unistd/write.c
@@ -3,7 +3,7 @@
 
 ssize_t write(int fd, const void *buf, size_t count)
 {
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 	__wasi_ciovec_t iov = {
 		.buf = buf,
 		.buf_len = count
diff --git a/system/lib/libc/musl/src/unistd/writev.c b/system/lib/libc/musl/src/unistd/writev.c
index 443d14f35d1be..4e81f107f61fb 100644
--- a/system/lib/libc/musl/src/unistd/writev.c
+++ b/system/lib/libc/musl/src/unistd/writev.c
@@ -1,12 +1,12 @@
 #include <sys/uio.h>
 #include "syscall.h"
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 #include <wasi/api.h>
 #endif
 
 ssize_t writev(int fd, const struct iovec *iov, int count)
 {
-#if __EMSCRIPTEN__
+#ifdef __EMSCRIPTEN__
 	size_t num;
 	if (__wasi_syscall_ret(__wasi_fd_write(fd, (struct __wasi_ciovec_t*)iov, count, &num))) {
 		return -1;