Strace: Move output formatting to separate function

Moving the formatting of strace's output into a separate function will
allow us to introduce more complexity into the formatting logic without
touching the main body of the program.

The new function uses a switch statement to select how to format the
arguments and result depending on the syscall. At this point we only
include the default formatting, where the registers are simply dumped,
but later on we can add specializations for each system call we want to
support.

Userland/Utilities/strace.cpp

@@ -20,6 +20,12 @@
 
 static int g_pid = -1;
 
+#if ARCH(I386)
+using syscall_arg_t = u32;
+#else
+using syscall_arg_t = u64;
+#endif
+
 static void handle_sigint(int)
 {
     if (g_pid == -1)
@@ -30,6 +36,26 @@ static void handle_sigint(int)
     }
 }
 
+static String format_syscall(syscall_arg_t syscall_index, syscall_arg_t arg1, syscall_arg_t arg2, syscall_arg_t arg3, syscall_arg_t res)
+{
+    auto syscall_function = (Syscall::Function)syscall_index;
+    StringBuilder builder;
+    builder.append(Syscall::to_string(syscall_function));
+    builder.append('(');
+
+    switch (syscall_function) {
+    default:
+        builder.appendff("{:#08x}, {:#08x}, {:#08x})\t={}",
+            arg1,
+            arg2,
+            arg3,
+            res);
+    }
+
+    builder.append('\n');
+    return builder.to_string();
+}
+
 int main(int argc, char** argv)
 {
     if (pledge("stdio wpath cpath proc exec ptrace sigaction", nullptr) < 0) {
@@ -129,15 +155,15 @@ int main(int argc, char** argv)
             return 1;
         }
 #if ARCH(I386)
-        u32 syscall_index = regs.eax;
-        u32 arg1 = regs.edx;
-        u32 arg2 = regs.ecx;
-        u32 arg3 = regs.ebx;
+        syscall_arg_t syscall_index = regs.eax;
+        syscall_arg_t arg1 = regs.edx;
+        syscall_arg_t arg2 = regs.ecx;
+        syscall_arg_t arg3 = regs.ebx;
 #else
-        u64 syscall_index = regs.rax;
-        u64 arg1 = regs.rdx;
-        u64 arg2 = regs.rcx;
-        u64 arg3 = regs.rbx;
+        syscall_arg_t syscall_index = regs.rax;
+        syscall_arg_t arg1 = regs.rdx;
+        syscall_arg_t arg2 = regs.rcx;
+        syscall_arg_t arg3 = regs.rbx;
 #endif
 
         if (ptrace(PT_SYSCALL, g_pid, 0, 0) == -1) {
@@ -160,12 +186,7 @@ int main(int argc, char** argv)
         u64 res = regs.rax;
 #endif
 
-        auto string = String::formatted("{}({:#08x}, {:#08x}, {:#08x})\t={}\n",
-            Syscall::to_string((Syscall::Function)syscall_index),
-            arg1,
-            arg2,
-            arg3,
-            res);
+        auto string = format_syscall(syscall_index, arg1, arg2, arg3, res);
 
         if (!trace_file->write(string)) {
             warnln("write: {}", trace_file->error_string());