diff --git a/system/lib/libc/musl/arch/emscripten/bits/alltypes.h b/system/lib/libc/musl/arch/emscripten/bits/alltypes.h
index 3599062069ac0..83b834246fbf0 100644
--- a/system/lib/libc/musl/arch/emscripten/bits/alltypes.h
+++ b/system/lib/libc/musl/arch/emscripten/bits/alltypes.h
@@ -1,61 +1,59 @@
-#define __LITTLE_ENDIAN 1234
-#define __BIG_ENDIAN 4321
-#define __USE_TIME_BITS64 1
-
-#define __BYTE_ORDER __LITTLE_ENDIAN
-
-#define __LONG_MAX  __LONG_MAX__
-
+/*
+ * The .h version of this file is generated from the .h.in.
+ * See update_alltypes.sh.
+ */
 #define _Addr __PTRDIFF_TYPE__
 #define _Int64 __INT64_TYPE__
 #define _Reg __PTRDIFF_TYPE__
 
-#if __GNUC__ >= 3
-#if defined(__NEED_va_list) && !defined(__DEFINED_va_list)
-typedef __builtin_va_list va_list;
-#define __DEFINED_va_list
-#endif
+#define __BYTE_ORDER 1234
+#define __LONG_MAX __LONG_MAX__
 
-#if defined(__NEED___isoc_va_list) && !defined(__DEFINED___isoc_va_list)
-typedef __builtin_va_list __isoc_va_list;
-#define __DEFINED___isoc_va_list
+#ifndef __cplusplus
+#if defined(__NEED_wchar_t) && !defined(__DEFINED_wchar_t)
+typedef __WCHAR_TYPE__ wchar_t;
+#define __DEFINED_wchar_t
 #endif
 
-#else
-#if defined(__NEED_va_list) && !defined(__DEFINED_va_list)
-typedef struct __va_list * va_list;
-#define __DEFINED_va_list
 #endif
-
-#if defined(__NEED___isoc_va_list) && !defined(__DEFINED___isoc_va_list)
-typedef struct __va_list * __isoc_va_list;
-#define __DEFINED___isoc_va_list
+#if defined(__NEED_wint_t) && !defined(__DEFINED_wint_t)
+typedef __WINT_TYPE__ wint_t;
+#define __DEFINED_wint_t
 #endif
 
+
+// XXX EMSCRIPTEN: ensure it's always 32-bits even in wasm64
+#if defined(__NEED_blkcnt_t) && !defined(__DEFINED_blkcnt_t)
+typedef int blkcnt_t;
+#define __DEFINED_blkcnt_t
 #endif
 
-#ifndef __cplusplus
-#ifdef __WCHAR_TYPE__
-#if defined(__NEED_wchar_t) && !defined(__DEFINED_wchar_t)
-typedef __WCHAR_TYPE__ wchar_t;
-#define __DEFINED_wchar_t
+#if defined(__NEED_blksize_t) && !defined(__DEFINED_blksize_t)
+typedef int blksize_t;
+#define __DEFINED_blksize_t
 #endif
 
-#else
-#if defined(__NEED_wchar_t) && !defined(__DEFINED_wchar_t)
-typedef int wchar_t;
-#define __DEFINED_wchar_t
+#if defined(__NEED_clock_t) && !defined(__DEFINED_clock_t)
+typedef int clock_t;
+#define __DEFINED_clock_t
 #endif
 
+#if defined(__NEED_dev_t) && !defined(__DEFINED_dev_t)
+typedef unsigned int dev_t;
+#define __DEFINED_dev_t
 #endif
+
+#if defined(__NEED_suseconds_t) && !defined(__DEFINED_suseconds_t)
+typedef int suseconds_t;
+#define __DEFINED_suseconds_t
 #endif
-#if defined(__NEED_wint_t) && !defined(__DEFINED_wint_t)
-typedef __WINT_TYPE__ wint_t;
-#define __DEFINED_wint_t
+
+#if defined(__NEED_wctype_t) && !defined(__DEFINED_wctype_t)
+typedef unsigned int wctype_t;
+#define __DEFINED_wctype_t
 #endif
 
 
-#if defined(__FLT_EVAL_METHOD__) && __FLT_EVAL_METHOD__ == 0
 #if defined(__NEED_float_t) && !defined(__DEFINED_float_t)
 typedef float float_t;
 #define __DEFINED_float_t
@@ -66,76 +64,54 @@ typedef double double_t;
 #define __DEFINED_double_t
 #endif
 
-#else
-#if defined(__NEED_float_t) && !defined(__DEFINED_float_t)
-typedef long double float_t;
-#define __DEFINED_float_t
-#endif
 
-#if defined(__NEED_double_t) && !defined(__DEFINED_double_t)
-typedef long double double_t;
-#define __DEFINED_double_t
+#ifndef __cplusplus
+#if defined(__NEED_max_align_t) && !defined(__DEFINED_max_align_t)
+typedef struct { _Alignas(8) long long __ll; long double __ld; } max_align_t;
+#define __DEFINED_max_align_t
 #endif
 
+#elif defined(__GNUC__)
+#if defined(__NEED_max_align_t) && !defined(__DEFINED_max_align_t)
+typedef struct { __attribute__((__aligned__(8))) long long __ll; long double __ld; } max_align_t;
+#define __DEFINED_max_align_t
 #endif
 
-#if defined(__NEED_time_t) && !defined(__DEFINED_time_t)
-typedef _Int64 time_t;
-#define __DEFINED_time_t
+#else
+#if defined(__NEED_max_align_t) && !defined(__DEFINED_max_align_t)
+typedef struct { alignas(8) long long __ll; long double __ld; } max_align_t;
+#define __DEFINED_max_align_t
 #endif
 
-#if defined(__NEED_suseconds_t) && !defined(__DEFINED_suseconds_t)
-typedef int suseconds_t; /* XXX EMSCRIPTEN: ensure it's always 32-bits even in wasm64 */
-#define __DEFINED_suseconds_t
 #endif
 
-
+// For canvas transfer implementation in Emscripten, use an extra control field
+// to pass a pointer to a string denoting the WebGL canvases to transfer.
 #if defined(__NEED_pthread_attr_t) && !defined(__DEFINED_pthread_attr_t)
-typedef struct {
-    union {
-        int __i[10];
-        volatile int __vi[10];
-        unsigned long __s[10];
-    } __u;
-#ifdef __EMSCRIPTEN__
-    // For canvas transfer implementation in Emscripten, use an extra control field
-    // to pass a pointer to a string denoting the WebGL canvases to transfer.
-    const char *_a_transferredcanvases;
-#endif
-} pthread_attr_t;
+typedef struct { union { int __i[10]; volatile int __vi[10]; unsigned long __s[10]; } __u; const char *_a_transferredcanvases; } pthread_attr_t;
 #define __DEFINED_pthread_attr_t
 #endif
 
+
+// TODO(kleisauke): Remove these two typedefs.
 #if defined(__NEED_pthread_mutex_t) && !defined(__DEFINED_pthread_mutex_t)
-typedef struct { union { int __i[6]; volatile int __vi[6]; volatile void *__p[6]; } __u; } pthread_mutex_t;
+typedef struct { union { int __i[6]; volatile int __vi[6]; volatile void * /*volatile*/__p[6]; } __u; } pthread_mutex_t;
 #define __DEFINED_pthread_mutex_t
 #endif
 
 #if defined(__NEED_mtx_t) && !defined(__DEFINED_mtx_t)
-typedef struct { union { int __i[6]; volatile int __vi[6]; volatile void *__p[6]; } __u; } mtx_t;
+typedef struct { union { int __i[6]; volatile int __vi[6]; volatile void * /*volatile*/__p[6]; } __u; } mtx_t;
 #define __DEFINED_mtx_t
 #endif
 
-#if defined(__NEED_pthread_cond_t) && !defined(__DEFINED_pthread_cond_t)
-typedef struct { union { int __i[12]; volatile int __vi[12]; void *__p[12]; } __u; } pthread_cond_t;
-#define __DEFINED_pthread_cond_t
-#endif
-
-#if defined(__NEED_cnd_t) && !defined(__DEFINED_cnd_t)
-typedef struct { union { int __i[12]; volatile int __vi[12]; void *__p[12]; } __u; } cnd_t;
-#define __DEFINED_cnd_t
-#endif
-
-#if defined(__NEED_pthread_rwlock_t) && !defined(__DEFINED_pthread_rwlock_t)
-typedef struct { union { int __i[sizeof(long)==8?14:8]; volatile int __vi[sizeof(long)==8?14:8]; void *__p[sizeof(long)==8?7:8]; } __u; } pthread_rwlock_t;
-#define __DEFINED_pthread_rwlock_t
-#endif
-
-#if defined(__NEED_pthread_barrier_t) && !defined(__DEFINED_pthread_barrier_t)
-typedef struct { union { int __i[5]; volatile int __vi[5]; void *__p[5]; } __u; } pthread_barrier_t;
-#define __DEFINED_pthread_barrier_t
-#endif
 
+// END EMSCRIPTEN-SPECIFIC DEFINITIONS
+//
+// Below here are the shared musl definitions.  The emscripten-specific definitions above will take precedence
+// due to the `__DEFINED_` macro system.
+#define __LITTLE_ENDIAN 1234
+#define __BIG_ENDIAN 4321
+#define __USE_TIME_BITS64 1
 
 #if defined(__NEED_size_t) && !defined(__DEFINED_size_t)
 typedef unsigned _Addr size_t;
@@ -172,6 +148,16 @@ typedef _Reg register_t;
 #define __DEFINED_register_t
 #endif
 
+#if defined(__NEED_time_t) && !defined(__DEFINED_time_t)
+typedef _Int64 time_t;
+#define __DEFINED_time_t
+#endif
+
+#if defined(__NEED_suseconds_t) && !defined(__DEFINED_suseconds_t)
+typedef _Int64 suseconds_t;
+#define __DEFINED_suseconds_t
+#endif
+
 
 #if defined(__NEED_int8_t) && !defined(__DEFINED_int8_t)
 typedef signed char     int8_t;
@@ -179,22 +165,22 @@ typedef signed char     int8_t;
 #endif
 
 #if defined(__NEED_int16_t) && !defined(__DEFINED_int16_t)
-typedef short           int16_t;
+typedef signed short    int16_t;
 #define __DEFINED_int16_t
 #endif
 
 #if defined(__NEED_int32_t) && !defined(__DEFINED_int32_t)
-typedef int             int32_t;
+typedef signed int      int32_t;
 #define __DEFINED_int32_t
 #endif
 
 #if defined(__NEED_int64_t) && !defined(__DEFINED_int64_t)
-typedef _Int64          int64_t;
+typedef signed _Int64   int64_t;
 #define __DEFINED_int64_t
 #endif
 
 #if defined(__NEED_intmax_t) && !defined(__DEFINED_intmax_t)
-typedef _Int64          intmax_t;
+typedef signed _Int64   intmax_t;
 #define __DEFINED_intmax_t
 #endif
 
@@ -250,17 +236,17 @@ typedef unsigned _Int64 ino_t;
 #endif
 
 #if defined(__NEED_dev_t) && !defined(__DEFINED_dev_t)
-typedef unsigned int dev_t;
+typedef unsigned _Int64 dev_t;
 #define __DEFINED_dev_t
 #endif
 
 #if defined(__NEED_blksize_t) && !defined(__DEFINED_blksize_t)
-typedef int blksize_t; /* XXX EMSCRIPTEN: ensure it's always 32-bits even in wasm64 */
+typedef long blksize_t;
 #define __DEFINED_blksize_t
 #endif
 
 #if defined(__NEED_blkcnt_t) && !defined(__DEFINED_blkcnt_t)
-typedef int blkcnt_t;
+typedef _Int64 blkcnt_t;
 #define __DEFINED_blkcnt_t
 #endif
 
@@ -274,13 +260,14 @@ typedef unsigned _Int64 fsfilcnt_t;
 #define __DEFINED_fsfilcnt_t
 #endif
 
+
 #if defined(__NEED_wint_t) && !defined(__DEFINED_wint_t)
 typedef unsigned wint_t;
 #define __DEFINED_wint_t
 #endif
 
 #if defined(__NEED_wctype_t) && !defined(__DEFINED_wctype_t)
-typedef unsigned int wctype_t; /* XXX EMSCRIPTEN: ensure it's always 32-bits even in wasm64 */
+typedef unsigned long wctype_t;
 #define __DEFINED_wctype_t
 #endif
 
@@ -296,22 +283,17 @@ typedef int clockid_t;
 #endif
 
 #if defined(__NEED_clock_t) && !defined(__DEFINED_clock_t)
-typedef int clock_t;  /* XXX EMSCRIPTEN: ensure it's always 32-bits even in wasm64 */
+typedef long clock_t;
 #define __DEFINED_clock_t
 #endif
 
-#if defined(__NEED_max_align_t) && !defined(__DEFINED_max_align_t)
-typedef struct { long long __ll; long double __ld; } max_align_t;
-#define __DEFINED_max_align_t
-#endif
-
 #if defined(__NEED_struct_timeval) && !defined(__DEFINED_struct_timeval)
 struct timeval { time_t tv_sec; suseconds_t tv_usec; };
 #define __DEFINED_struct_timeval
 #endif
 
 #if defined(__NEED_struct_timespec) && !defined(__DEFINED_struct_timespec)
-struct timespec { time_t tv_sec; long tv_nsec; };
+struct timespec { time_t tv_sec; int :8*(sizeof(time_t)-sizeof(long))*(__BYTE_ORDER==4321); long tv_nsec; int :8*(sizeof(time_t)-sizeof(long))*(__BYTE_ORDER!=4321); };
 #define __DEFINED_struct_timespec
 #endif
 
@@ -396,12 +378,28 @@ typedef struct { unsigned __attr[2]; } pthread_rwlockattr_t;
 #endif
 
 
+#if defined(__NEED_struct__IO_FILE) && !defined(__DEFINED_struct__IO_FILE)
+struct _IO_FILE { char __x; };
+#define __DEFINED_struct__IO_FILE
+#endif
+
 #if defined(__NEED_FILE) && !defined(__DEFINED_FILE)
 typedef struct _IO_FILE FILE;
 #define __DEFINED_FILE
 #endif
 
 
+#if defined(__NEED_va_list) && !defined(__DEFINED_va_list)
+typedef __builtin_va_list va_list;
+#define __DEFINED_va_list
+#endif
+
+#if defined(__NEED___isoc_va_list) && !defined(__DEFINED___isoc_va_list)
+typedef __builtin_va_list __isoc_va_list;
+#define __DEFINED___isoc_va_list
+#endif
+
+
 #if defined(__NEED_mbstate_t) && !defined(__DEFINED_mbstate_t)
 typedef struct __mbstate_t { unsigned __opaque1, __opaque2; } mbstate_t;
 #define __DEFINED_mbstate_t
@@ -443,6 +441,42 @@ typedef unsigned short sa_family_t;
 #endif
 
 
+#if defined(__NEED_pthread_attr_t) && !defined(__DEFINED_pthread_attr_t)
+typedef struct { union { int __i[sizeof(long)==8?14:9]; volatile int __vi[sizeof(long)==8?14:9]; unsigned long __s[sizeof(long)==8?7:9]; } __u; } pthread_attr_t;
+#define __DEFINED_pthread_attr_t
+#endif
+
+#if defined(__NEED_pthread_mutex_t) && !defined(__DEFINED_pthread_mutex_t)
+typedef struct { union { int __i[sizeof(long)==8?10:6]; volatile int __vi[sizeof(long)==8?10:6]; volatile void *volatile __p[sizeof(long)==8?5:6]; } __u; } pthread_mutex_t;
+#define __DEFINED_pthread_mutex_t
+#endif
+
+#if defined(__NEED_mtx_t) && !defined(__DEFINED_mtx_t)
+typedef struct { union { int __i[sizeof(long)==8?10:6]; volatile int __vi[sizeof(long)==8?10:6]; volatile void *volatile __p[sizeof(long)==8?5:6]; } __u; } mtx_t;
+#define __DEFINED_mtx_t
+#endif
+
+#if defined(__NEED_pthread_cond_t) && !defined(__DEFINED_pthread_cond_t)
+typedef struct { union { int __i[12]; volatile int __vi[12]; void *__p[12*sizeof(int)/sizeof(void*)]; } __u; } pthread_cond_t;
+#define __DEFINED_pthread_cond_t
+#endif
+
+#if defined(__NEED_cnd_t) && !defined(__DEFINED_cnd_t)
+typedef struct { union { int __i[12]; volatile int __vi[12]; void *__p[12*sizeof(int)/sizeof(void*)]; } __u; } cnd_t;
+#define __DEFINED_cnd_t
+#endif
+
+#if defined(__NEED_pthread_rwlock_t) && !defined(__DEFINED_pthread_rwlock_t)
+typedef struct { union { int __i[sizeof(long)==8?14:8]; volatile int __vi[sizeof(long)==8?14:8]; void *__p[sizeof(long)==8?7:8]; } __u; } pthread_rwlock_t;
+#define __DEFINED_pthread_rwlock_t
+#endif
+
+#if defined(__NEED_pthread_barrier_t) && !defined(__DEFINED_pthread_barrier_t)
+typedef struct { union { int __i[sizeof(long)==8?8:5]; volatile int __vi[sizeof(long)==8?8:5]; void *__p[sizeof(long)==8?4:5]; } __u; } pthread_barrier_t;
+#define __DEFINED_pthread_barrier_t
+#endif
+
+
 #undef _Addr
 #undef _Int64
 #undef _Reg
diff --git a/system/lib/libc/musl/arch/emscripten/bits/alltypes.h.in b/system/lib/libc/musl/arch/emscripten/bits/alltypes.h.in
index fc922d01f4ac4..5eced059b4372 100644
--- a/system/lib/libc/musl/arch/emscripten/bits/alltypes.h.in
+++ b/system/lib/libc/musl/arch/emscripten/bits/alltypes.h.in
@@ -1,25 +1,47 @@
+/*
+ * The .h version of this file is generated from the .h.in.
+ * See update_alltypes.sh.
+ */
 #define _Addr __PTRDIFF_TYPE__
 #define _Int64 __INT64_TYPE__
 #define _Reg __PTRDIFF_TYPE__
 
-TYPEDEF __builtin_va_list va_list;
-TYPEDEF __builtin_va_list __isoc_va_list;
+#define __BYTE_ORDER 1234
+#define __LONG_MAX __LONG_MAX__
 
 #ifndef __cplusplus
-TYPEDEF unsigned wchar_t;
+TYPEDEF __WCHAR_TYPE__ wchar_t;
 #endif
-TYPEDEF unsigned wint_t;
+TYPEDEF __WINT_TYPE__ wint_t;
+
+// XXX EMSCRIPTEN: ensure it's always 32-bits even in wasm64
+TYPEDEF int blkcnt_t;
+TYPEDEF int blksize_t;
+TYPEDEF int clock_t;
+TYPEDEF unsigned int dev_t;
+TYPEDEF int suseconds_t;
+TYPEDEF unsigned int wctype_t;
 
 TYPEDEF float float_t;
 TYPEDEF double double_t;
 
-TYPEDEF struct { long long __ll; long double __ld; } max_align_t;
-TYPEDEF long time_t;
-TYPEDEF long suseconds_t;
+#ifndef __cplusplus
+TYPEDEF struct { _Alignas(8) long long __ll; long double __ld; } max_align_t;
+#elif defined(__GNUC__)
+TYPEDEF struct { __attribute__((__aligned__(8))) long long __ll; long double __ld; } max_align_t;
+#else
+TYPEDEF struct { alignas(8) long long __ll; long double __ld; } max_align_t;
+#endif
+
+// For canvas transfer implementation in Emscripten, use an extra control field
+// to pass a pointer to a string denoting the WebGL canvases to transfer.
+TYPEDEF struct { union { int __i[10]; volatile int __vi[10]; unsigned long __s[10]; } __u; const char *_a_transferredcanvases; } pthread_attr_t;
 
-TYPEDEF struct { union { int __i[10]; unsigned __s[10]; } __u; } pthread_attr_t;
-TYPEDEF struct { union { int __i[7]; void *__p[7]; } __u; } pthread_mutex_t;
-TYPEDEF struct { union { int __i[12]; void *__p[12]; } __u; } pthread_cond_t;
-TYPEDEF struct { union { int __i[8]; void *__p[8]; } __u; } pthread_rwlock_t;
-TYPEDEF struct { union { int __i[5]; void *__p[5]; } __u; } pthread_barrier_t;
+// TODO(kleisauke): Remove these two typedefs.
+TYPEDEF struct { union { int __i[6]; volatile int __vi[6]; volatile void * /*volatile*/__p[6]; } __u; } pthread_mutex_t;
+TYPEDEF struct { union { int __i[6]; volatile int __vi[6]; volatile void * /*volatile*/__p[6]; } __u; } mtx_t;
 
+// END EMSCRIPTEN-SPECIFIC DEFINITIONS
+//
+// Below here are the shared musl definitions.  The emscripten-specific definitions above will take precedence
+// due to the `__DEFINED_` macro system.
diff --git a/system/lib/libc/musl/tools/mkalltypes.sed b/system/lib/libc/musl/tools/mkalltypes.sed
new file mode 100644
index 0000000000000..fa15efc35f64e
--- /dev/null
+++ b/system/lib/libc/musl/tools/mkalltypes.sed
@@ -0,0 +1,15 @@
+/^TYPEDEF/s/TYPEDEF \(.*\) \([^ ]*\);$/#if defined(__NEED_\2) \&\& !defined(__DEFINED_\2)\
+typedef \1 \2;\
+#define __DEFINED_\2\
+#endif\
+/
+/^STRUCT/s/STRUCT * \([^ ]*\) \(.*\);$/#if defined(__NEED_struct_\1) \&\& !defined(__DEFINED_struct_\1)\
+struct \1 \2;\
+#define __DEFINED_struct_\1\
+#endif\
+/
+/^UNION/s/UNION * \([^ ]*\) \(.*\);$/#if defined(__NEED_union_\1) \&\& !defined(__DEFINED_union_\1)\
+union \1 \2;\
+#define __DEFINED_union_\1\
+#endif\
+/
diff --git a/system/lib/libc/update_alltypes.sh b/system/lib/libc/update_alltypes.sh
new file mode 100755
index 0000000000000..5892c9815554e
--- /dev/null
+++ b/system/lib/libc/update_alltypes.sh
@@ -0,0 +1,10 @@
+#!/bin/sh
+# This script updates alltypes.h based on the contents of alltypes.h.in.
+# In upstream this must be done by the top level Makefile.
+
+musl_srcdir="$PWD/musl"
+musl_includedir="$musl_srcdir/include"
+emscripten_dir="$musl_srcdir/arch/emscripten/bits"
+sed -f $musl_srcdir/tools/mkalltypes.sed \
+  $emscripten_dir/alltypes.h.in \
+  $musl_includedir/alltypes.h.in > $emscripten_dir/alltypes.h