From 73d81d13cab886e72d7743a64b3358b6cc65a30a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?John=20T=C3=B6rnblom?= <john.tornblom@gmail.com>
Date: Thu, 31 Aug 2023 23:42:53 +0200
Subject: [PATCH 1/2] add arbitrary syscall function

---
 crt/crt.c     |  2 ++
 crt/syscall.c | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+)
 create mode 100644 crt/syscall.c

diff --git a/crt/crt.c b/crt/crt.c
index cba5739..8197ea6 100644
--- a/crt/crt.c
+++ b/crt/crt.c
@@ -15,6 +15,8 @@
 extern int payload_main(struct payload_args *args);
 extern int libc_init();
 extern int libkernel_init();
+extern int syscall_init();
+
 
 void __ps5sdk_crt_start(struct payload_args *args)
 {
diff --git a/crt/syscall.c b/crt/syscall.c
new file mode 100644
index 0000000..adb37c1
--- /dev/null
+++ b/crt/syscall.c
@@ -0,0 +1,33 @@
+/*****************************************************
+ * PS5 SDK - Syscall
+ * Implements the syscall() function by setting up
+ * registers manually, then jumping to a syscall
+ * instruction in libkernel.
+ ****************************************************/
+
+#include <ps5/payload_main.h>
+
+static __attribute__ ((used)) long ptr_syscall;
+
+asm(".intel_syntax noprefix\n"
+    ".global syscall\n"
+    ".type syscall @function\n"
+    "syscall:\n"
+    "  mov rax, rdi\n"                      // sysno
+    "  mov rdi, rsi\n"                      // arg1
+    "  mov rsi, rdx\n"                      // arg2
+    "  mov rdx, rcx\n"                      // arg3
+    "  mov r10, r8\n"                       // arg4
+    "  mov r8,  r9\n"                       // arg5
+    "  mov r9,  qword ptr [rsp + 8]\n"      // arg6
+    "  jmp qword ptr [rip + ptr_syscall]\n" // syscall
+    "  ret\n"
+    );
+
+int syscall_init(const struct payload_args *args) {
+	if(args->dlsym(0x2001, "getpid", &ptr_syscall)) {
+		return -1;
+	}
+	ptr_syscall += 0xa;
+	return 0;
+}

From 5dae4cc8d3f7480cd2f30b5cf52c82dfc37c2035 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?John=20T=C3=B6rnblom?= <john.tornblom@gmail.com>
Date: Fri, 1 Sep 2023 00:40:14 +0200
Subject: [PATCH 2/2] init syscall() from crt

---
 crt/crt.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/crt/crt.c b/crt/crt.c
index 8197ea6..d726661 100644
--- a/crt/crt.c
+++ b/crt/crt.c
@@ -11,8 +11,10 @@
 #define ERR_CRT_UNKNOWN             0xDEAD0000
 #define ERR_CRT_LIBKERNEL_INIT_FAIL 0xDEAD0001
 #define ERR_CRT_MODULE_INIT_FAIL    0xDEAD0002
+#define ERR_CRT_SYSCALL_INIT_FAIL   0xDEAD0003
 
 extern int payload_main(struct payload_args *args);
+extern int syscall_init(struct payload_args *args);
 extern int libc_init();
 extern int libkernel_init();
 extern int syscall_init();
@@ -25,7 +27,12 @@ void __ps5sdk_crt_start(struct payload_args *args)
 	// Dlsym must be initialized first to resolve everything else
 	init_dlsym(args->dlsym);
 
-	// Kickstart libkernel and libc
+	// Kickstart syscall, libkernel and libc
+	if (syscall_init(args) != 0) {
+		rv = ERR_CRT_SYSCALL_INIT_FAIL;
+		goto out;
+	}
+
 	if (libkernel_init() != 0) {
 		rv = ERR_CRT_LIBKERNEL_INIT_FAIL;
 		goto out;