Add config option to delay libc initialisation

The initialisation of libc should occur after system calls have been
initalised. Some calls are initialised externally or have external
dependencies.

Signed-off-by: Curtis Millar <curtis.millar@data61.csiro.au>

libsel4muslcsys/CMakeLists.txt

diff --git a/libsel4muslcsys/CMakeLists.txt b/libsel4muslcsys/CMakeLists.txt
index c7ae46f..336a75c 100644
--- a/libsel4muslcsys/CMakeLists.txt
+++ b/libsel4muslcsys/CMakeLists.txt
@@ -53,6 +53,17 @@
     DEFAULT
     OFF
 )
+
+config_string(
+    LibSel4MuslcSysConstructorPriority
+    LIB_SEL4_MUSLC_SYS_CONSTRUCTOR_PRIORITY
+    "Set the priority of the muslc initialisation constructors such that
+	they occur after external initialisation of the system call
+	dependencies."
+    DEFAULT
+    "CONSTRUCTOR_MIN_PRIORITY + 1"
+    UNQUOTE
+)
 mark_as_advanced(
     LibSel4MuslcSysMorecoreBytes
     LibSel4MuslcSysDebugHalt

libsel4muslcsys/src/vsyscall.c

diff --git a/libsel4muslcsys/src/vsyscall.c b/libsel4muslcsys/src/vsyscall.c
index e9f1b4e..bad8ace 100644
--- a/libsel4muslcsys/src/vsyscall.c
+++ b/libsel4muslcsys/src/vsyscall.c
@@ -221,7 +221,7 @@
  * it can be overriden. We are able to have this constructor
  * in this file since we know it will get looked at by the linker due
  * to __vsyscall_ptr being here */
-static void CONSTRUCTOR(CONSTRUCTOR_MIN_PRIORITY + 1) init_syscall_table(void)
+static void CONSTRUCTOR(CONSTRUCTOR_MIN_PRIORITY) init_syscall_table(void)
 {
     muslcsys_syscall_t ret UNUSED;
     ret = muslcsys_install_syscall(__NR_set_tid_address, sys_set_tid_address);
@@ -242,7 +242,7 @@
 #ifdef CONFIG_LIB_SEL4_MUSLC_SYS_CPIO_FS
 extern char _cpio_archive[];
 extern char _cpio_archive_end[];
-static void CONSTRUCTOR(CONSTRUCTOR_MIN_PRIORITY + 1) install_default_cpio(void)
+static void CONSTRUCTOR(CONSTRUCTOR_MIN_PRIORITY) install_default_cpio(void)
 {
     unsigned long cpio_len = _cpio_archive_end - _cpio_archive;
     muslcsys_install_cpio_interface(_cpio_archive, cpio_len, cpio_get_file);
@@ -300,7 +300,7 @@
 extern void __init_libc(char const *const *envp, char const *pn);
 
 /* Initialise muslc environment */
-void CONSTRUCTOR(CONSTRUCTOR_MIN_PRIORITY) muslcsys_init_muslc(void)
+void CONSTRUCTOR(CONFIG_LIB_SEL4_MUSLC_SYS_CONSTRUCTOR_PRIORITY) muslcsys_init_muslc(void)
 {
     seL4_IPCBuffer *tmp = __sel4_ipc_buffer;
     __init_libc(sel4runtime_envp(), sel4runtime_argv()[0]);