a.cpp

// Include the most common headers from the C standard library
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>

// Include the main libnx system header, for Switch development
#include <switch.h>

// Size of the inner heap (adjust as necessary).
#define INNER_HEAP_SIZE 0x80000

extern "C" {

// Sysmodules should not use applet*.
u32 __nx_applet_type = AppletType_None;

// Sysmodules will normally only want to use one FS session.
u32 __nx_fs_num_sessions = 1;

// Newlib heap configuration function (makes malloc/free work).
void __libnx_initheap(void)
{
    static char inner_heap[INNER_HEAP_SIZE];
    extern char* fake_heap_start;
    extern char* fake_heap_end;

    // Configure the newlib heap.
    fake_heap_start = inner_heap;
    fake_heap_end   = inner_heap + sizeof(inner_heap);
}

// Service initialization.
void __appInit(void) {
    // for (int i = 0; i < 10; i++) {
    //     svcSleepThread(1e+9L);
    // }
    Result rc;

    // Open a service manager session.
    rc = smInitialize();
    if (R_FAILED(rc))
        diagAbortWithResult(MAKERESULT(Module_Libnx, LibnxError_InitFail_SM));

    // Retrieve the current version of Horizon OS.
    rc = setsysInitialize();
    if (R_SUCCEEDED(rc)) {
        SetSysFirmwareVersion fw;
        rc = setsysGetFirmwareVersion(&fw);
        if (R_SUCCEEDED(rc))
            hosversionSet(MAKEHOSVERSION(fw.major, fw.minor, fw.micro));
        setsysExit();
    }

    // Disable this if you don't want to use the filesystem.
    rc = fsInitialize();
    if (R_FAILED(rc))
        diagAbortWithResult(MAKERESULT(Module_Libnx, LibnxError_InitFail_FS));

    // Disable this if you don't want to use the SD card filesystem.
    fsdevMountSdmc();

    // Add other services you want to use here.
    if (R_FAILED(rc = pmdmntInitialize()))
        fatalThrow(rc);

    // Close the service manager session.
    smExit();
}

// Service deinitialization.
void __appExit(void) {
    // Close extra services you added to __appInit here.
    pmdmntExit();
    fsdevUnmountAll(); // Disable this if you don't want to use the SD card filesystem.
    fsExit(); // Disable this if you don't want to use the filesystem.
}

} // extern "C"

namespace {

Mutex log_mutex{};

void log(const char* format, ...) {
    mutexLock(&log_mutex);
    auto f = fopen("/sys-patch.txt", "a");
    va_list args;
    va_start(args, format);
    vfprintf(f, format, args);
    va_end(args);
    fclose(f);
    mutexUnlock(&log_mutex);
}

struct DebugEventInfo {
    u32 event_type;
    u32 flags;
    u64 thread_id;
    u64 title_id;
    u64 process_id;
    char process_name[12];
    u32 mmu_flags;
    u8 _0x30[0x10];
};
static_assert(sizeof(DebugEventInfo) == 0x40);

bool find_and_open_process(u64 tid, Handle* handle_out) {
    Handle handle{};
    DebugEventInfo event_info{};

    u64 pids[200]{};
    s32 process_count{};

    // this never fails
    if (R_FAILED(svcGetProcessList(&process_count, pids, 200))) {
        log("failed to get process count???\n");
        return false;
    }
    log("process_count: %d\n", process_count);

    for (s32 i = 0; i < (process_count - 1); i++) {
        log("[%d] checking pid: 0x%08lX\n", i, pids[i]);
        // freezes here at i=4 and i=6
        if (R_SUCCEEDED(svcDebugActiveProcess(&handle, pids[i]))) {
            log("success svcDebugActiveProcess %d id: 0x%08lX\n", i, pids[i]);
            if (R_SUCCEEDED(svcGetDebugEvent(&event_info, handle))) {
                log("success svcGetDebugEvent %d id: 0x%08lX name: %s\n", i, pids[i], event_info.process_name);
                if (event_info.title_id == tid) {
                    log("got handle!\n");
                    *handle_out = handle;
                    return true;
                } else {
                    log("found the wrong tid: 0x%08lX %d id: 0x%08lX name: %s\n", event_info.title_id, i, pids[i], event_info.process_name);
                }
            } else {
                log("failed to svcGetDebugEvent: %d id: 0x%08lX\n", i, pids[i]);
            }
        } else {
            log("failed to debug active process: %d id: 0x%08lX\n", i, pids[i]);
        }

        if (handle) {
            log("closing handle\n");
            svcCloseHandle(handle);
            handle = 0;
        }
    }

    return false;
}

} // namespace

// Main program entrypoint
int main(int argc, char* argv[]) {
    // Initialization code can go here.
    // Your code / main loop goes here.
    // If you need threads, you can use threadCreate etc.
    mutexInit(&log_mutex);

    remove("/sys-patch.txt");
    log("hello world\n");

    // this never returns because the switch hangs within the process.
    constexpr u64 fs_tid = 0x0100000000000000;
    Handle fs_handle{};
    if (!find_and_open_process(fs_tid, &fs_handle)) {
        log("failed to get process handle :(\n");
    } else {
        log("got process handle :)\n");
    }

    for (;;) {
        svcSleepThread(1e+9L); // 1sec sleep
    }

    // Deinitialization and resources clean up code can go here.
    return 0;
}

a.json

{
	"name":	"a",
	"title_id":	"0x420000000000000B",
	"title_id_range_min":	"0x420000000000000B",
	"title_id_range_max":	"0x420000000000000B",
	"main_thread_stack_size":	"0x4000",
	"main_thread_priority":	49,
	"default_cpu_id":	3,
	"process_category":	1,
	"is_retail":	true,
	"pool_partition":	2,
	"is_64_bit":	true,
	"address_space_type":	1,
	"filesystem_access":	{
		"permissions":	"0xffffffffffffffff"
	},
	"service_access":	["*"],
	"service_host":	["*"],
	"kernel_capabilities":	[{
			"type":	"kernel_flags",
			"value":	{
				"highest_thread_priority":	63,
				"lowest_thread_priority":	24,
				"lowest_cpu_id":	3,
				"highest_cpu_id":	3
			}
		}, {
			"type":	"syscalls",
			"value":	{
				"svcUnknown":	"0x00",
				"svcSetHeapSize":	"0x01",
				"svcSetMemoryPermission":	"0x02",
				"svcSetMemoryAttribute":	"0x03",
				"svcMapMemory":	"0x04",
				"svcUnmapMemory":	"0x05",
				"svcQueryMemory":	"0x06",
				"svcExitProcess":	"0x07",
				"svcCreateThread":	"0x08",
				"svcStartThread":	"0x09",
				"svcExitThread":	"0x0a",
				"svcSleepThread":	"0x0b",
				"svcGetThreadPriority":	"0x0c",
				"svcSetThreadPriority":	"0x0d",
				"svcGetThreadCoreMask":	"0x0e",
				"svcSetThreadCoreMask":	"0x0f",
				"svcGetCurrentProcessorNumber":	"0x10",
				"svcSignalEvent":	"0x11",
				"svcClearEvent":	"0x12",
				"svcMapSharedMemory":	"0x13",
				"svcUnmapSharedMemory":	"0x14",
				"svcCreateTransferMemory":	"0x15",
				"svcCloseHandle":	"0x16",
				"svcResetSignal":	"0x17",
				"svcWaitSynchronization":	"0x18",
				"svcCancelSynchronization":	"0x19",
				"svcArbitrateLock":	"0x1a",
				"svcArbitrateUnlock":	"0x1b",
				"svcWaitProcessWideKeyAtomic":	"0x1c",
				"svcSignalProcessWideKey":	"0x1d",
				"svcGetSystemTick":	"0x1e",
				"svcConnectToNamedPort":	"0x1f",
				"svcSendSyncRequestLight":	"0x20",
				"svcSendSyncRequest":	"0x21",
				"svcSendSyncRequestWithUserBuffer":	"0x22",
				"svcSendAsyncRequestWithUserBuffer":	"0x23",
				"svcGetProcessId":	"0x24",
				"svcGetThreadId":	"0x25",
				"svcBreak":	"0x26",
				"svcOutputDebugString":	"0x27",
				"svcReturnFromException":	"0x28",
				"svcGetInfo":	"0x29",
				"svcFlushEntireDataCache":	"0x2a",
				"svcFlushDataCache":	"0x2b",
				"svcMapPhysicalMemory":	"0x2c",
				"svcUnmapPhysicalMemory":	"0x2d",
				"svcGetFutureThreadInfo":	"0x2e",
				"svcGetLastThreadInfo":	"0x2f",
				"svcGetResourceLimitLimitValue":	"0x30",
				"svcGetResourceLimitCurrentValue":	"0x31",
				"svcSetThreadActivity":	"0x32",
				"svcGetThreadContext3":	"0x33",
				"svcWaitForAddress":	"0x34",
				"svcSignalToAddress":	"0x35",
				"svcUnknown":	"0x36",
				"svcUnknown":	"0x37",
				"svcUnknown":	"0x38",
				"svcUnknown":	"0x39",
				"svcUnknown":	"0x3a",
				"svcUnknown":	"0x3b",
				"svcDumpInfo":	"0x3c",
				"svcDumpInfoNew":	"0x3d",
				"svcUnknown":	"0x3e",
				"svcUnknown":	"0x3f",
				"svcCreateSession":	"0x40",
				"svcAcceptSession":	"0x41",
				"svcReplyAndReceiveLight":	"0x42",
				"svcReplyAndReceive":	"0x43",
				"svcReplyAndReceiveWithUserBuffer":	"0x44",
				"svcCreateEvent":	"0x45",
				"svcUnknown":	"0x46",
				"svcUnknown":	"0x47",
				"svcMapPhysicalMemoryUnsafe":	"0x48",
				"svcUnmapPhysicalMemoryUnsafe":	"0x49",
				"svcSetUnsafeLimit":	"0x4a",
				"svcCreateCodeMemory":	"0x4b",
				"svcControlCodeMemory":	"0x4c",
				"svcSleepSystem":	"0x4d",
				"svcReadWriteRegister":	"0x4e",
				"svcSetProcessActivity":	"0x4f",
				"svcCreateSharedMemory":	"0x50",
				"svcMapTransferMemory":	"0x51",
				"svcUnmapTransferMemory":	"0x52",
				"svcCreateInterruptEvent":	"0x53",
				"svcQueryPhysicalAddress":	"0x54",
				"svcQueryIoMapping":	"0x55",
				"svcCreateDeviceAddressSpace":	"0x56",
				"svcAttachDeviceAddressSpace":	"0x57",
				"svcDetachDeviceAddressSpace":	"0x58",
				"svcMapDeviceAddressSpaceByForce":	"0x59",
				"svcMapDeviceAddressSpaceAligned":	"0x5a",
				"svcMapDeviceAddressSpace":	"0x5b",
				"svcUnmapDeviceAddressSpace":	"0x5c",
				"svcInvalidateProcessDataCache":	"0x5d",
				"svcStoreProcessDataCache":	"0x5e",
				"svcFlushProcessDataCache":	"0x5f",
				"svcDebugActiveProcess":	"0x60",
				"svcBreakDebugProcess":	"0x61",
				"svcTerminateDebugProcess":	"0x62",
				"svcGetDebugEvent":	"0x63",
				"svcContinueDebugEvent":	"0x64",
				"svcGetProcessList":	"0x65",
				"svcGetThreadList":	"0x66",
				"svcGetDebugThreadContext":	"0x67",
				"svcSetDebugThreadContext":	"0x68",
				"svcQueryDebugProcessMemory":	"0x69",
				"svcReadDebugProcessMemory":	"0x6a",
				"svcWriteDebugProcessMemory":	"0x6b",
				"svcSetHardwareBreakPoint":	"0x6c",
				"svcGetDebugThreadParam":	"0x6d",
				"svcUnknown":	"0x6e",
				"svcGetSystemInfo":	"0x6f",
				"svcCreatePort":	"0x70",
				"svcManageNamedPort":	"0x71",
				"svcConnectToPort":	"0x72",
				"svcSetProcessMemoryPermission":	"0x73",
				"svcMapProcessMemory":	"0x74",
				"svcUnmapProcessMemory":	"0x75",
				"svcQueryProcessMemory":	"0x76",
				"svcMapProcessCodeMemory":	"0x77",
				"svcUnmapProcessCodeMemory":	"0x78",
				"svcCreateProcess":	"0x79",
				"svcStartProcess":	"0x7a",
				"svcTerminateProcess":	"0x7b",
				"svcGetProcessInfo":	"0x7c",
				"svcCreateResourceLimit":	"0x7d",
				"svcSetResourceLimitLimitValue":	"0x7e",
				"svcCallSecureMonitor":	"0x7f"
			}
		}, {
			"type":	"min_kernel_version",
			"value":	"0x0030"
		}, {
			"type":	"handle_table_size",
			"value":	1023
		}, {
			"type":	"debug_flags",
			"value":	{
				"allow_debug":	true,
				"force_debug":	true
			}
	}]
}

log.txt

hello world
process_count: 62
[0] checking pid: 0x00000001
success svcDebugActiveProcess 0 id: 0x00000001
success svcGetDebugEvent 0 id: 0x00000001 name: Loader
found the wrong tid: 0x100000000000001 0 id: 0x00000001 name: Loader
closing handle
[1] checking pid: 0x00000002
success svcDebugActiveProcess 1 id: 0x00000002
success svcGetDebugEvent 1 id: 0x00000002 name: sm
found the wrong tid: 0x100000000000004 1 id: 0x00000002 name: sm
closing handle
[2] checking pid: 0x00000003
success svcDebugActiveProcess 2 id: 0x00000003
success svcGetDebugEvent 2 id: 0x00000003 name: spl
found the wrong tid: 0x100000000000028 2 id: 0x00000003 name: spl
closing handle
[3] checking pid: 0x00000004