kern: optimize logging for release kernel strings (saves printf space in .text)

libraries/libmesosphere/include/mesosphere/kern_debug_log.hpp

@@ -28,6 +28,8 @@ namespace ams::kern {
             static NOINLINE void Printf(const char *format, ...) __attribute__((format(printf, 1, 2)));
             static NOINLINE void VPrintf(const char *format, ::std::va_list vl);
 
+            static NOINLINE void LogException(const char *str);
+
             static NOINLINE Result PrintUserString(ams::kern::svc::KUserPointer<const char *> user_str, size_t len);
 
             /* Functionality for preserving across sleep. */
@@ -49,6 +51,8 @@ namespace ams::kern {
 
 #endif
 
+#define MESOSPHERE_EXCEPTION_LOG(str) ::ams::kern::KDebugLog::LogException(str)
+
 #define MESOSPHERE_RELEASE_LOG(fmt, ...) ::ams::kern::KDebugLog::Printf((fmt), ## __VA_ARGS__)
 #define MESOSPHERE_RELEASE_VLOG(fmt, vl) ::ams::kern::KDebugLog::VPrintf((fmt), (vl))
 

libraries/libmesosphere/source/arch/arm64/kern_exception_handlers.cpp

@@ -308,7 +308,7 @@ namespace ams::kern::arch::arm64 {
                 {
                     if (ec != EsrEc_SoftwareStepEl0) {
                         /* If the exception wasn't single-step, print details. */
-                        MESOSPHERE_RELEASE_LOG("Exception occurred. %016lx\n", GetCurrentProcess().GetProgramId());
+                        MESOSPHERE_EXCEPTION_LOG("Exception occurred. ");
 
                         {
                             /* Print the current thread's registers. */
@@ -327,7 +327,7 @@ namespace ams::kern::arch::arm64 {
                 #else
                 {
                     /* Print that an exception occurred. */
-                    MESOSPHERE_RELEASE_LOG("Exception occurred. %016lx\n", GetCurrentProcess().GetProgramId());
+                    MESOSPHERE_EXCEPTION_LOG("Exception occurred. ");
 
                     {
                         /* Print the current thread's registers. */
@@ -496,7 +496,7 @@ namespace ams::kern::arch::arm64 {
         }
 
         /* Print that an exception occurred. */
-        MESOSPHERE_RELEASE_LOG("Exception occurred. %016lx\n", GetCurrentProcess().GetProgramId());
+        MESOSPHERE_EXCEPTION_LOG("Exception occurred. ");
 
         /* Exit the current process. */
         GetCurrentProcess().Exit();

libraries/libmesosphere/source/kern_debug_log.cpp

@@ -20,15 +20,15 @@ namespace ams::kern {
 
     namespace {
 
-        KSpinLock g_debug_log_lock;
+        constinit KSpinLock g_debug_log_lock;
-        bool      g_initialized_impl;
+        constinit bool      g_initialized_impl;
 
         /* NOTE: Nintendo's print buffer is size 0x100. */
-        char g_print_buffer[0x400];
+        constinit char g_print_buffer[0x400];
 
         void PutString(const char *str) {
             /* Only print if the implementation is initialized. */
-            if (!g_initialized_impl) {
+            if (AMS_UNLIKELY(!g_initialized_impl)) {
                 return;
             }
 
@@ -73,6 +73,20 @@ namespace ams::kern {
 
         #endif
 
+        ALWAYS_INLINE void FormatU64(char * const dst, u64 value) {
+            /* Adjust, so that we can print the value backwards. */
+            char *cur = dst + 2 * sizeof(value);
+
+            /* Format the value in (as %016lx) */
+            while (cur > dst) {
+                /* Extract the digit. */
+                const auto digit = value & 0xF;
+                value >>= 4;
+
+                *(--cur) = (digit <= 9) ? ('0' + digit) : ('a' + digit - 10);
+            }
+        }
+
     }
 
     void KDebugLog::Initialize() {
@@ -109,6 +123,33 @@ namespace ams::kern {
         ::ams::util::TVSNPrintf(dst, dst_size, format, vl);
     }
 
+    void KDebugLog::LogException(const char *str) {
+        if (KTargetSystem::IsDebugLoggingEnabled()) {
+            /* Get the current program ID. */
+            /* NOTE: Nintendo does this after printing the string, */
+            /* but it seems wise to avoid holding the lock/disabling interrupts */
+            /* for longer than is strictly necessary. */
+            char suffix[18];
+            if (const auto *cur_process = GetCurrentProcessPointer(); AMS_LIKELY(cur_process != nullptr)) {
+                FormatU64(suffix, cur_process->GetProgramId());
+                suffix[16] = '\n';
+                suffix[17] = '\x00';
+            } else {
+                suffix[0] = '\n';
+                suffix[1] = '\x00';
+            }
+
+            KScopedInterruptDisable di;
+            KScopedSpinLock lk(g_debug_log_lock);
+
+            /* Log the string. */
+            PutString(str);
+
+            /* Log the program id (and newline) suffix. */
+            PutString(suffix);
+        }
+    }
+
     Result KDebugLog::PrintUserString(ams::kern::svc::KUserPointer<const char *> user_str, size_t len) {
         /* If printing is enabled, print the user string. */
         #if defined(MESOSPHERE_ENABLE_DEBUG_PRINT)

libraries/libmesosphere/source/svc/kern_svc_exception.cpp

@@ -60,7 +60,7 @@ namespace ams::kern::svc {
             }
 
             /* Print that break was called. */
-            MESOSPHERE_RELEASE_LOG("Break() called. %016lx\n", GetCurrentProcess().GetProgramId());
+            MESOSPHERE_EXCEPTION_LOG("Break() called. ");
 
             /* Try to enter JIT debug state. */
             if (GetCurrentProcess().EnterJitDebug(ams::svc::DebugEvent_Exception, ams::svc::DebugException_UserBreak, KDebug::GetProgramCounter(GetCurrentThread()), break_reason, address, size)) {