the sandbox caching of thread id's only works with glibc
see: https://gitlab.alpinelinux.org/alpine/aports/-/merge_requests/32356
see: https://gitlab.alpinelinux.org/alpine/aports/-/issues/13579
--
--- a/sandbox/linux/services/namespace_sandbox.cc
+++ b/sandbox/linux/services/namespace_sandbox.cc
@@ -209,6 +209,70 @@
   return base::LaunchProcess(argv, launch_options_copy);
 }
 
+#if defined(__aarch64__)
+#define TLS_ABOVE_TP
+#endif
+
+struct musl_pthread
+{
+  /* Part 1 -- these fields may be external or
+  * internal (accessed via asm) ABI. Do not change. */
+  struct pthread *self;
+#ifndef TLS_ABOVE_TP
+  uintptr_t *dtv;
+#endif
+  struct pthread *prev, *next; /* non-ABI */
+  uintptr_t sysinfo;
+#ifndef TLS_ABOVE_TP
+#ifdef CANARY_PAD
+  uintptr_t canary_pad;
+#endif
+  uintptr_t canary;
+#endif
+
+/* Part 2 -- implementation details, non-ABI. */
+  int tid;
+  int errno_val;
+  volatile int detach_state;
+  volatile int cancel;
+  volatile unsigned char canceldisable, cancelasync;
+  unsigned char tsd_used:1;
+  unsigned char dlerror_flag:1;
+  unsigned char *map_base;
+  size_t map_size;
+  void *stack;
+  size_t stack_size;
+  size_t guard_size;
+  void *result;
+  struct __ptcb *cancelbuf;
+  void **tsd;
+  struct {
+    volatile void *volatile head;
+    long off;
+    volatile void *volatile pending;
+  } robust_list;
+  int h_errno_val;
+  volatile int timer_id;
+  locale_t locale;
+  volatile int killlock[1];
+  char *dlerror_buf;
+  void *stdio_locks;
+
+  /* Part 3 -- the positions of these fields relative to
+  * the end of the structure is external and internal ABI. */
+#ifdef TLS_ABOVE_TP
+  uintptr_t canary;
+  uintptr_t *dtv;
+#endif
+};
+
+void MaybeUpdateMuslTidCache()
+{
+  pid_t real_tid = sys_gettid();
+  pid_t* cached_tid_location = &reinterpret_cast<struct musl_pthread*>(pthread_self())->tid;
+  *cached_tid_location = real_tid;
+}
+
 // static
 pid_t NamespaceSandbox::ForkInNewPidNamespace(bool drop_capabilities_in_child) {
   const pid_t pid =
@@ -226,6 +290,7 @@
 #if defined(LIBC_GLIBC)
     MaybeUpdateGlibcTidCache();
 #endif
+    MaybeUpdateMuslTidCache();
     return 0;
   }
 
