From b3e6571586ededd4e12a2d796b6a79efeb8d0728 Mon Sep 17 00:00:00 2001
From: Michael Scire <SciresM@gmail.com>
Date: Fri, 14 Feb 2020 04:01:09 -0800
Subject: [PATCH] kern: improve panic output

---
 libraries/libmesosphere/source/kern_panic.cpp | 101 +++++++++++++-----
 1 file changed, 74 insertions(+), 27 deletions(-)

diff --git a/libraries/libmesosphere/source/kern_panic.cpp b/libraries/libmesosphere/source/kern_panic.cpp
index eb58d853c..a60e88093 100644
--- a/libraries/libmesosphere/source/kern_panic.cpp
+++ b/libraries/libmesosphere/source/kern_panic.cpp
@@ -29,33 +29,81 @@ namespace ams::kern {
 
     namespace {
 
-        size_t g_panic_count = 0;
+        constexpr std::array<s32, cpu::NumCores> NegativeArray = [] {
+            std::array<s32, cpu::NumCores> arr = {};
+            for (size_t i = 0; i < arr.size(); i++) {
+                arr[i] = -1;
+            }
+            return arr;
+        }();
+
+        std::atomic<s32> g_next_ticket    = 0;
+        std::atomic<s32> g_current_ticket = 0;
+
+        std::array<s32, cpu::NumCores> g_core_tickets = NegativeArray;
+
+        s32 GetCoreTicket() {
+            const s32 core_id = GetCurrentCoreId();
+            if (g_core_tickets[core_id] == -1) {
+                g_core_tickets[core_id] = 2 * g_next_ticket.fetch_add(1);
+            }
+            return g_core_tickets[core_id];
+        }
+
+        void WaitCoreTicket() {
+            const s32 expected = GetCoreTicket();
+            const s32 desired  = expected + 1;
+            s32 compare = g_current_ticket;
+            do {
+                if (compare == desired) {
+                    break;
+                }
+                compare = expected;
+            } while (!g_current_ticket.compare_exchange_weak(compare, desired));
+        }
+
+        void ReleaseCoreTicket() {
+            const s32 expected = GetCoreTicket() + 1;
+            const s32 desired  = expected + 1;
+            s32 compare = g_current_ticket;
+            do {
+                if (compare != expected) {
+                    break;
+                }
+            } while (!g_current_ticket.compare_exchange_weak(compare, desired));
+        }
 
         [[gnu::unused]] void PrintCurrentState() {
-            if (g_panic_count == 1) {
-                g_panic_count++;
+            /* Wait for it to be our turn to print. */
+            WaitCoreTicket();
 
-                MESOSPHERE_RELEASE_LOG("Base Address: %p\n", _start);
+            const s32 core_id = GetCurrentCoreId();
+            MESOSPHERE_RELEASE_LOG("Core[%d] Current State:\n", core_id);
 
-                /* TODO: Dump register state. */
+            /* TODO: Dump register state. */
 
-                #ifdef ATMOSPHERE_ARCH_ARM64
-                    MESOSPHERE_RELEASE_LOG("Backtrace:\n");
-                    uintptr_t fp = reinterpret_cast<uintptr_t>(__builtin_frame_address(0));
-                    for (size_t i = 0; i < 32 && fp && util::IsAligned(fp, 0x10) && cpu::GetPhysicalAddressWritable(nullptr, fp, true); i++) {
-                        struct {
-                            uintptr_t fp;
-                            uintptr_t lr;
-                        } *stack_frame = reinterpret_cast<decltype(stack_frame)>(fp);
-                        MESOSPHERE_RELEASE_LOG("    [%02zx]: %p\n", i, reinterpret_cast<void *>(stack_frame->lr));
-                        fp = stack_frame->fp;
-                    }
-                #endif
-            }
+            #ifdef ATMOSPHERE_ARCH_ARM64
+                MESOSPHERE_RELEASE_LOG("    Backtrace:\n");
+                uintptr_t fp = reinterpret_cast<uintptr_t>(__builtin_frame_address(0));
+                for (size_t i = 0; i < 32 && fp && util::IsAligned(fp, 0x10) && cpu::GetPhysicalAddressWritable(nullptr, fp, true); i++) {
+                    struct {
+                        uintptr_t fp;
+                        uintptr_t lr;
+                    } *stack_frame = reinterpret_cast<decltype(stack_frame)>(fp);
+                    MESOSPHERE_RELEASE_LOG("        [%02zx]: %p\n", i, reinterpret_cast<void *>(stack_frame->lr));
+                    fp = stack_frame->fp;
+                }
+            #endif
+
+            MESOSPHERE_RELEASE_LOG("\n");
+
+            /* Allow the next core to print. */
+            ReleaseCoreTicket();
         }
 
         NORETURN void StopSystem() {
             #ifdef MESOSPHERE_BUILD_FOR_DEBUGGING
+                /* Print the current core. */
                 PrintCurrentState();
             #endif
 
@@ -66,16 +114,15 @@ namespace ams::kern {
 
     NORETURN WEAK_SYMBOL void Panic(const char *file, int line, const char *format, ...) {
         #ifdef MESOSPHERE_BUILD_FOR_DEBUGGING
-            if (g_panic_count == 0) {
-                g_panic_count++;
+            /* Wait for it to be our turn to print. */
+            WaitCoreTicket();
 
-                ::std::va_list vl;
-                va_start(vl, format);
-                MESOSPHERE_RELEASE_LOG("KernelPanic (Core %d): %s:%d\n", GetCurrentCoreId(), file, line);
-                MESOSPHERE_RELEASE_VLOG(format, vl);
-                MESOSPHERE_RELEASE_LOG("\n");
-                va_end(vl);
-            }
+            ::std::va_list vl;
+            va_start(vl, format);
+            MESOSPHERE_RELEASE_LOG("Core[%d]: Kernel Panic at %s:%d\n", GetCurrentCoreId(), file, line);
+            MESOSPHERE_RELEASE_VLOG(format, vl);
+            MESOSPHERE_RELEASE_LOG("\n");
+            va_end(vl);
         #endif
 
         StopSystem();