a lot of cleanup, added pmp

Makefile

@@ -1,23 +1,9 @@
 # small makefile for compiling the kernel
 
-# kernel lib dir
-KLIBDIR=kinclude
-# object file dir
-ODIR=obj
-# target dir
-TARGET=out
-
-GCC_PREF=riscv32-unknown-elf-
-
-CC=$(GCC_PREF)gcc
-OBJDUMP=$(GCC_PREF)objdump
-CFLAGS=-I$(KLIBDIR) -MD -mcmodel=medany -Wall -Wextra -pedantic-errors -Wno-builtin-declaration-mismatch
-KERNEL_CFLAGS=-nostdlib -T linker.ld
-ARCH = rv32im
-
 ### Build configuration:
-# Define the maximum number of running processes
+# process and binary count
 PROCESS_COUNT = 8
+PACKAGED_BINARY_COUNT = 8
 
 # Define the maximum number of binaries packaged with the kernel
 PACKAGED_BINARY_COUNT = 4
@@ -25,17 +11,34 @@ PACKAGED_BINARY_COUNT = 4
 # Comment this out if you don't have any text IO device memory mapped
 CFLAGS += -DTEXT_IO_ADDR=0xff0000 -DTEXT_IO_BUFLEN=64
 
-# Uncomment these to build with only the rv32i standard
+# If you want to build without any extension, you can uncomment the next line
 #CFLAGS += -D__risc_no_ext=1
-#ARCH = rv32i
+# also change this to represent your target RISC-V architecture and extensions
+ARCH = rv32im
 
 # Configure if mtime is memory-mapped or inside a CSR:
 # replace 0xFF11FF22FF33 with the correct address
 #CFLAGS += -DTIMECMP_IN_MEMORY=1 -DTIMECMP_MEM_ADDR=0xFF11FF22
 
+# Set this to the first out-of-bounds memory address
+END_OF_USABLE_MEM=0xff0000
 
 ### End configuration
-CFLAGS += -march=$(ARCH) -DPROCESS_COUNT=$(PROCESS_COUNT) -DNUM_BINARIES=$(PACKAGED_BINARY_COUNT)
+
+# kernel lib dir
+KLIBDIR=kinclude
+# object file dir
+ODIR=obj
+# target dir
+TARGET=out
+
+GCC_PREF=riscv32-unknown-elf-
+
+CC=$(GCC_PREF)gcc
+OBJDUMP=$(GCC_PREF)objdump
+CFLAGS+=-I$(KLIBDIR) -MD -mcmodel=medany -Wall -Wextra -pedantic-errors -Wno-builtin-declaration-mismatch -march=$(ARCH)
+KERNEL_CFLAGS=-nostdlib -T linker.ld
+CFLAGS+=-DPROCESS_COUNT=$(PROCESS_COUNT) -DPACKAGED_BINARY_COUNT=$(PACKAGED_BINARY_COUNT) -DEND_OF_USABLE_MEM=$(END_OF_USABLE_MEM)
 
 # dependencies that need to be built:
 _DEPS = ecall.c csr.c sched.c io.c malloc.c

kernel.c

@@ -4,20 +4,26 @@
 #include "sched.h"
 #include "io.h"
 #include "malloc.h"
+#include "csr.h"
 
 void read_binary_table();
-
+void setup_mem_protection();
-extern struct process_control_block processes[PROCESS_COUNT];
 
 // this array is populated when the memory image is built, therefore it should
 // resign in a section which is not overwritten with zeros on startup
-loaded_binary binary_table[NUM_BINARIES] __attribute__ ((section(".data")));
+loaded_binary binary_table[PACKAGED_BINARY_COUNT] __attribute__ ((section(".data")));
 
+// access the memset function defined in boot.S
 extern void memset(unsigned int, void*, void*);
 
+// access linker symbols:
+extern byte* _end, _ftext;
+
 extern void init()
 {
     dbgln("Kernel started!", 15);
+    // setup phsycial memory protection
+    setup_mem_protection();
     // initialize scheduler
     scheudler_init();
     // initialize tabel for associating ecall codes with their handlers
@@ -33,13 +39,13 @@ void read_binary_table()
 {
     char msg[28] = "found bin with id 0 at pos 0";
 
-    malloc_info info = {
+    struct malloc_info info = {
-        .allocate_memory_end    = (void*) 0xFF0000,
+        .allocate_memory_end    = (void*) END_OF_USABLE_MEM,
         .allocate_memory_start  = (void*) 0
     };
 
     // calculate the end of loaded binaries
-    for (int i = 0; i < NUM_BINARIES; i++) {
+    for (int i = 0; i < PACKAGED_BINARY_COUNT; i++) {
         if (binary_table[i].binid == 0)
             break;
 
@@ -56,15 +62,34 @@ void read_binary_table()
     // initialize malloc
     malloc_init(&info);
 
-    for (int i = 0; i < NUM_BINARIES; i++) {
+    for (int i = 0; i < PACKAGED_BINARY_COUNT; i++) {
         if (binary_table[i].binid == 0)
             break;
 
         // create a new process for each binary found
         // it should have around 4kb stack
-        optional_pcbptr res = create_new_process(binary_table + i, 1 << 12);
+        optional_pcbptr res = create_new_process(binary_table + i);
         if (has_error(res)) {
             dbgln("Error creating initial process!", 31);
         }
     }
 }
+
+void setup_mem_protection()
+{
+    // this pmp config uses Top-of-Range mode - read more in the privileged spec p.49
+    // we disallow all access to 0x0-0x100 from user and machine mode
+    // and all access to 0x100-kernel_end from user mode
+    // to do this, we must first calculate the kernel bin length
+    uint32 kernel_bin_len = ((uint32) &_end) - ((uint32) &_ftext);
+
+    CSR_WRITE(CSR_PMPADDR, 0x100);
+    CSR_WRITE(CSR_PMPADDR + 1, 0x100 + kernel_bin_len);
+
+    // this contains two pmp configs:
+    // fields:    L    A  RWX
+    // pmpcfg0: 0b1_00_01_000 <- disallow RWX from U and M mode
+    // pmpcfg1: 0b0_00_01_000 <- disallow RWX from U mode
+    // the resulint number is 0b0000100010001000, hex 0x888
+    CSR_WRITE(CSR_PMPCFG, 0x888);
+}

kinclude/csr.c

@@ -1,3 +1,4 @@
+#include "ktypes.h"
 #include "csr.h"
 
 #ifdef TIMECMP_IN_MEMORY
@@ -6,10 +7,10 @@
 #error "You set TIMECMP_IN_MEMORY but did not provide a memory addres in TIMECMP_MEM_ADDR!"
 #endif
 
-void write_mtimecmp(unsigned long long int mtimecmp)
+void write_mtimecmp(uint64 mtimecmp)
 {
-    unsigned int lo = mtimecmp & 0xffffffff;
+    uint32 lo = mtimecmp & 0xffffffff;
-    unsigned int hi = mtimecmp >> 32;
+    uint32 hi = mtimecmp >> 32;
 
     __asm__ volatile (
           "li t0, %0\n"
@@ -21,10 +22,10 @@ void write_mtimecmp(unsigned long long int mtimecmp)
 
 #else
 
-void write_mtimecmp(unsigned long long int mtimecmp)
+void write_mtimecmp(uint64 mtimecmp)
 {
-    unsigned int lower = mtimecmp & 0xffffffff;
+    uint32 lower = mtimecmp & 0xffffffff;
-    unsigned int higher = mtimecmp >> 32;
+    uint32 higher = mtimecmp >> 32;
 
     __asm__ volatile (
           "csrw %0, %2\n"

kinclude/csr.h

@@ -16,6 +16,9 @@
 #define CSR_MTIMECMP    0x780       // mtimecmp register for timer interrupts
 #define CSR_MTIMECMPH   0x781       // mtimecmph register for timer interrupts
 
+#define CSR_PMPCFG      0x3A0       // start of physical memory protection config
+#define CSR_PMPADDR     0x3B0       // start of pmp addresses
+
 #ifndef CSR_HALT
 #define CSR_HALT        0x789       // writing nonzero value here will halt the cpu
 #endif
@@ -35,9 +38,9 @@
         __asm__ ("csrw %0, %1" :: "I"(CSR_HALT), "I"(code)); \
 }
 
-void write_mtimecmp(unsigned long long int mtimecmp);
+void write_mtimecmp(uint64 mtimecmp);
 
-inline __attribute__((always_inline)) unsigned long long int read_time()
+inline __attribute__((always_inline)) uint64 read_time()
 {
     unsigned int lower, higher;
 
@@ -47,7 +50,7 @@ inline __attribute__((always_inline)) unsigned long long int read_time()
           : "=r"(lower), "=r"(higher)
           : "i"(CSR_TIME), "i"(CSR_TIMEH)
     );
-    return (unsigned long long) higher << 32 | lower;
+    return (uint64) higher << 32 | lower;
 }
 
 #endif

kinclude/ecall.c

@@ -16,12 +16,15 @@ ecall_handler ecall_table[ECALL_TABLE_LEN] = { 0 };
 
 optional_int ecall_handle_spawn_thread(int* args_ptr, struct process_control_block* pcb)
 {
+    // args_ptr is a pointer to the pcb->regs field, starting at a0.
+    // args_ptr[0] is a0, args_ptr[1] is a1, etc.
     void* entry = (void*) args_ptr[0];  // a0
     void* args = (void*) args_ptr[1];   // a1
-    //int   flags = args_ptr[2];          // a2
 
-    optional_pcbptr pcb_or_err = create_new_thread(pcb, entry, args, 1 << 14);
+    // create a new thread
+    optional_pcbptr pcb_or_err = create_new_thread(pcb, entry, args);
 
+    // if an error occured, pass it along to the process
     if (has_error(pcb_or_err))
         return (optional_int) { .error = pcb_or_err.error };
 
@@ -30,12 +33,15 @@ optional_int ecall_handle_spawn_thread(int* args_ptr, struct process_control_blo
 
 optional_int ecall_handle_sleep(int* args, struct process_control_block* pcb)
 {
+    // read len from a0
     int len = args[0];
 
+    // only allow sleeping for positive intervals
     if (len < 0) {
         return (optional_int) { .error = EINVAL };
     }
 
+    // if a positive interval is given, calculate the wakeup time
     if (len > 0) {
         pcb->asleep_until = read_time() + len;
         pcb->status = PROC_WAIT_SLEEP;
@@ -46,28 +52,35 @@ optional_int ecall_handle_sleep(int* args, struct process_control_block* pcb)
 
 optional_int ecall_handle_join(int* args, struct process_control_block* pcb)
 {
-    int pid = args[0];  // a0
+    int pid = args[0];  // read pid from processes a0 register
 
+    // find the referenced process
     struct process_control_block* target = process_from_pid(pid);
 
     if (target == NULL)
         return (optional_int) { .error = ESRCH };
 
+    // if the process is dead, join can return immediately
     if (target->status == PROC_DEAD)
         return (optional_int) { .value = target->exit_code };
 
+    // mark the current process as waiting for the target process
     pcb->status = PROC_WAIT_PROC;
     pcb->waiting_for_process = target;
 
+    // check if a valid timeout was passed in register a1
     int timeout = args[1];
 
     if (timeout <= 0)
         return (optional_int) { .value = 0 };
 
+    // set the asleep_until field
     unsigned int len = (unsigned int) timeout;
 
     pcb->asleep_until = read_time() + len;
 
+    // here we can return whatever value we want, as it is overwritten when
+    // the process is awoken again
     return (optional_int) { .value = 0 };
 }
 
@@ -100,6 +113,7 @@ optional_int ecall_handle_exit(int* args, struct process_control_block* pcb)
     pcb->status = PROC_DEAD;
     pcb->exit_code = *args;
 
+    // print a message if debugging is enabled
     if (DEBUGGING) {
         char msg[34] = "process    exited with code   ";
 
@@ -119,10 +133,12 @@ optional_int ecall_handle_exit(int* args, struct process_control_block* pcb)
 
 void trap_handle_ecall()
 {
+    // save current clock so we don't waste too much process time
     mark_ecall_entry();
+    // get the current process
     struct process_control_block* pcb = get_current_process();
     int *regs = pcb->regs;
-    int code = regs[REG_A0 + 7];    // code is stored inside a7
+    int code = regs[REG_A0 + 7];    // syscall code is stored inside a7
 
     // check if the code is too large/small or if the handler is zero
     if (code < 0 || code > ECALL_TABLE_LEN || ecall_table[code] == NULL) {
@@ -154,7 +170,7 @@ void trap_handle(int interrupt_bit, int code, int mtval)
             scheduler_run_next();
             break;
         default:
-            // impossible
+            // any other interrupt is not supported currently
             HALT(12);
             break;
         }
@@ -187,6 +203,8 @@ void trap_handle(int interrupt_bit, int code, int mtval)
     __builtin_unreachable();
 }
 
+// this writes the function pointers to the ecall table
+// it's called from the kernels init() function
 void init_ecall_table()
 {
     ecall_table[ECALL_SPAWN] = ecall_handle_spawn_thread;
@@ -196,6 +214,8 @@ void init_ecall_table()
     ecall_table[ECALL_EXIT] = ecall_handle_exit;
 }
 
+// this exception handler is crude and just kills off any process who
+// causes an exception.
 void handle_exception(int ecode, int mtval)
 {
     // kill off offending process

kinclude/io.c

@@ -1,23 +1,33 @@
 #include "io.h"
+// this file should only be used for debugging purposes. Most functions here
+// could easily corrupt kernel memory if used with untrusted input.
+// ALWAYS check your buffer lengths!
 
 #ifdef TEXT_IO_ADDR
 
+// this function writes a string to the TEXT_IO buffer
+// it adds a newline at the end and splits the passed string into smaller chunks
+// if it is larger than TEXT_IO_BUFLEN.
 void dbgln(char* text, int len)
 {
+    // if the passed text is longer than TEXT_IO_BUFLEN, print it in chunks
     while (len > TEXT_IO_BUFLEN) {
         dbgln(text, TEXT_IO_BUFLEN);
         text += TEXT_IO_BUFLEN;
         len -= TEXT_IO_BUFLEN;
     }
 
+    // this is the address of the textIO
     char* ioaddr = (char*) TEXT_IO_ADDR + 4;
 
+    // write message bytewise to buffer (this could be implemented faster)
     for (int i = 0; i < len; i++) {
         if (*text == 0)
             break;
         *ioaddr++ = *text++;
     }
 
+    // add a newline
     if (len < TEXT_IO_BUFLEN)
         *ioaddr = '\n';
 
@@ -28,13 +38,16 @@ void dbgln(char* text, int len)
 
 /* alphabet for itoa */
 char alpha[16] = "0123456789abcdef";
+// convert int to str
 char* itoa(int value, char* str, int base)
 {
+    // fail on unknown base
     if (base > 16 || base < 2) {
         *str++ = '?';
         return str;
     }
 
+    // handle negative numbers
     if (value < 0) {
         *str++ = '-';
         value *= -1;
@@ -51,6 +64,7 @@ char* itoa(int value, char* str, int base)
         digits++;
     } while (value > 0);
 
+    // write reversed number to the buffer
     value = num;
     do {
         num = value % base;

kinclude/ktypes.h

@@ -1,8 +1,14 @@
 #ifndef H_ktypes
 #define H_ktypes
 
+// define the nullpointer
 #define NULL ((void*) 0)
 
+// types with explicit bit-widths
+typedef unsigned int uint32;
+typedef unsigned long long uint64;
+typedef unsigned char byte;
+
 /*
  * Error codes
  */

kinclude/malloc.c

@@ -5,7 +5,7 @@
 #include "io.h"
 
 // information about the systems memory layout is stored here
-static malloc_info global_malloc_info = { 0 };
+static struct malloc_info global_malloc_info = { 0 };
 // this pointer points to the end of unused memory
 static void* allocate_memory_end;
 // this stack holds currently unused program stacks
@@ -22,8 +22,11 @@ void stash_stack(void* stack_top)
     }
 }
 
-void malloc_init(malloc_info* given_info)
+// this function is called by the kernels init() function after it parsed the
+// list of loaded binaries and calculated the available memory for general allocation
+void malloc_init(struct malloc_info* given_info)
 {
+    // save the passed info
     global_malloc_info = *given_info;
     allocate_memory_end = given_info->allocate_memory_end;
     allocate_memory_end = (void*) (((int) allocate_memory_end) - PROCESS_COUNT);
@@ -53,6 +56,8 @@ optional_voidptr malloc_stack()
     return (optional_voidptr) { .value = stack_top };
 }
 
+// a stack is not returned to the general memory pool (since EMBARK has no such
+// pool) but rather just added to the pool of free process stacks.
 void free_stack(void* stack_top)
 {
     stash_stack(stack_top);

kinclude/malloc.h

@@ -3,14 +3,14 @@
 
 #include "ktypes.h"
 
-typedef struct malloc_info {
+struct malloc_info {
     void* allocate_memory_end;
     void* allocate_memory_start;
-} malloc_info;
+};
 
 optional_voidptr malloc_stack();
 void free_stack(void* stack_top);
 
-void malloc_init(malloc_info* info);
+void malloc_init(struct malloc_info* info);
 
 #endif

kinclude/sched.c

@@ -15,8 +15,8 @@ struct process_control_block processes[PROCESS_COUNT];
 // pointer to the currently scheduled process
 struct process_control_block* current_process = NULL;
 // timer variables to add kernel time back to the processes time slice
-unsigned long long int scheduling_interrupted_start;
+uint64 scheduling_interrupted_start;
-unsigned long long int next_interrupt_scheduled_for;
+uint64 next_interrupt_scheduled_for;
 // this counter generates process ids
 int next_process_id = 1;
 
@@ -60,7 +60,7 @@ void scheduler_try_return_to(struct process_control_block* pcb)
 // select a new process to run next
 struct process_control_block* scheduler_select_free()
 {
-    unsigned long long int mtime;
+    uint64 mtime;
     int timeout_available = 0; // note if a timeout is available
 
     while (1) {
@@ -122,6 +122,7 @@ struct process_control_block* scheduler_select_free()
     }
 }
 
+// performs the context switch from kernel to userspace mode
 void scheduler_switch_to(struct process_control_block* pcb)
 {
     CSR_WRITE(CSR_MEPC, pcb->pc);
@@ -167,6 +168,7 @@ void scheduler_switch_to(struct process_control_block* pcb)
     __builtin_unreachable();
 }
 
+// get a PCB from a pid
 struct process_control_block* process_from_pid(int pid)
 {
     for (int i = 0; i < PROCESS_COUNT; i++) {
@@ -186,6 +188,7 @@ struct process_control_block* get_current_process()
     return current_process;
 }
 
+// this method sets up the mtimecmp register to trigger the next timer interrupt
 void set_next_interrupt()
 {
     next_interrupt_scheduled_for = read_time() + TIME_SLICE_LEN;
@@ -197,14 +200,20 @@ void mark_ecall_entry()
     scheduling_interrupted_start = read_time();
 }
 
+// this function selects an unused entry in the processes list
+// it tries to select slots which have been unused the longest
 optional_pcbptr find_available_pcb_slot()
 {
+    // this method loops over the process list using an index which persists
+    // over multiple function calls, wrapping when it reaches the end. This
+    // makes free space selection relatively fair.
     static int index = 0;
     int start_index = index;
     struct process_control_block* pcb = processes + index;
 
     while (pcb->status != PROC_DEAD) {
         index = (index + 1) % PROCESS_COUNT;
+        // if we iterated over the whole list and found nothing, we have no space left!
         if (index == start_index)
             return (optional_pcbptr) { .error = ENOBUFS };
         pcb = processes + index;
@@ -214,9 +223,9 @@ optional_pcbptr find_available_pcb_slot()
     return (optional_pcbptr) { .value = pcb };
 }
 
-optional_pcbptr create_new_process(loaded_binary* bin, int stack_size)
+optional_pcbptr create_new_process(loaded_binary* bin)
 {
-    // try to get a position in the processes list
+    // try to get an unused entry in the processes list
     optional_pcbptr slot_or_err = find_available_pcb_slot();
 
     // if that failed, we cannot creat a new process
@@ -226,7 +235,7 @@ optional_pcbptr create_new_process(loaded_binary* bin, int stack_size)
     }
 
     // allocate stack for the new process
-    optional_voidptr stack_top_or_err = malloc_stack(stack_size); // allocate 4Kib stack
+    optional_voidptr stack_top_or_err = malloc_stack(); // allocate stack
 
     // if that failed, we also can't create a new process
     if (has_error(stack_top_or_err)) {
@@ -259,9 +268,9 @@ optional_pcbptr create_new_process(loaded_binary* bin, int stack_size)
     return (optional_pcbptr) { .value = pcb };
 }
 
-optional_pcbptr create_new_thread(struct process_control_block* parent, void* entrypoint, void* args, int stack_size)
+optional_pcbptr create_new_thread(struct process_control_block* parent, void* entrypoint, void* args)
 {
-    // try to get a position in the processes list
+    // try to get an unused entry in the processes list
     optional_pcbptr slot_or_err = find_available_pcb_slot();
 
     // if that failed, we cannot creat a new process
@@ -271,7 +280,7 @@ optional_pcbptr create_new_thread(struct process_control_block* parent, void* en
     }
 
     // allocate stack for the new process
-    optional_voidptr stack_top_or_err = malloc_stack(stack_size); // allocate 4Kib stack
+    optional_voidptr stack_top_or_err = malloc_stack(); // allocate stack
 
     // if that failed, we also can't create a new process
     if (has_error(stack_top_or_err)) {

kinclude/sched.h

@@ -20,8 +20,8 @@ struct process_control_block* get_current_process();
 void mark_ecall_entry();
 
 // process creation / destruction
-optional_pcbptr create_new_process(loaded_binary*, int);
+optional_pcbptr create_new_process(loaded_binary*);
-optional_pcbptr create_new_thread(struct process_control_block*, void*, void*, int);
+optional_pcbptr create_new_thread(struct process_control_block*, void*, void*);
 void destroy_process(struct process_control_block* pcb);
 void kill_child_processes(struct process_control_block* pcb);
 #endif

package.py

@@ -14,17 +14,8 @@ SECTOR_SIZE = 512
 # start address
 MEM_START = 0x100
 
-# this is the name of the global variable holding the list of loaded binaries
+# address where the userspace binaries should be located  (-1 to start directly after the kernel)
-KERNEL_BINARY_TABLE = 'binary_table'
+USR_BIN_START = -1
-# loaded_binary struct size (4 integers)
-KERNEL_BINARY_TABLE_ENTRY_SIZE = 4 * 4
-
-# overwrite this function to generate the entries for the loaded binary list
-def create_loaded_bin_struct(binid: int, entrypoint: int, start: int, end: int):
-    """
-    Creates the binary data to populate the KERNEL_BINARY_TABLE structs
-    """
-    return b''.join(num.to_bytes(4, 'little') for num in (binid, entrypoint, start, end))
 
 ## end of config
 
@@ -40,7 +31,23 @@ EMPTY_SECTIONS = set((
     '.bss', '.sbss', '.stack'
 ))
 
+# this is the name of the global variable holding the list of loaded binaries
+KERNEL_BINARY_TABLE = 'binary_table'
+# loaded_binary struct size (4 integers)
+KERNEL_BINARY_TABLE_ENTRY_SIZE = 4 * 4
+
+# overwrite this function to generate the entries for the loaded binary list
+def create_loaded_bin_struct(binid: int, entrypoint: int, start: int, end: int):
+    """
+    Creates the binary data to populate the KERNEL_BINARY_TABLE structs
+    """
+    return b''.join(num.to_bytes(4, 'little') for num in (binid, entrypoint, start, end))
+
+
 def overlaps(p1, l1, p2, l2) -> bool:
+    """
+    check if the intervals (p1, p1+l1) and (p2, p2+l2) overlap
+    """
     return (p1 <= p2 and p1 + l1 > p2) or (p2 <= p1 and p2 + l2 > p1)
 
 class Section:
@@ -202,6 +209,9 @@ def package(kernel: str, binaries: List[str], out: str):
 
     img.putBin(kernel)
 
+    if USR_BIN_START > 0:
+        img.seek(USR_BIN_START)
+
     binid = 0
     for bin_name in binaries:
         img.align(8) # align to eight bytes

programs/Makefile

@@ -11,5 +11,5 @@ spawn:
 thread:
 	$(CC) $(CFLAGS) -o threads threads.c
 
-all: simple spawn threads
+all: simple spawn thread
 

programs/spawn.c

@@ -110,22 +110,6 @@ char* itoa(int value, char* str, int base)
     return str;
 }
 
-void wrap_main()
-{
-    dbgln("start", 5);
-
-    register int code asm ("s1") = main();
-
-    dbgln("end", 3);
-
-    __asm__ __volatile__ (
-         "mv     a0, s1\n"
-         "li     a7, 5\n"
-         "ecall\n"
-         "ebreak\n"
-    );
-}
-
 void _start()
 {
     __asm__ __volatile__ (
@@ -134,6 +118,10 @@ void _start()
           "            la      gp, _gp\n"
           ".option pop\n"
     );
+    __asm__ __volatile__ (
+         "mv     a0, %0\n"
+         "li     a7, 5\n"
+         "ecall\n" :: "r"(main())
+    );
 
-    wrap_main();
 }

programs/threads.c

@@ -13,6 +13,7 @@ int main()
         return 1;
     }
     struct optional_int t2 = spawn(thread, &arg2);
+
     if (has_error(t2)) {
         __asm__ ("ebreak");
         return 2;
@@ -36,6 +37,7 @@ int thread(void* args)
 {
     // read value
     int arg = *((int*) args);
+
     //char buff[64] = "sleeping for ";
     //char* end = itoa(arg, &buff[13], 10);
 
@@ -118,12 +120,10 @@ void _start()
           "            la      gp, _gp\n"
           ".option pop\n"
     );
-
+    main();
-    register int code asm ("s1") = main();
     __asm__ __volatile__ (
-         "mv     a0, s1\n"
          "li     a7, 5\n"
          "ecall\n"
-         "ebreak\n"
     );
+    __builtin_unreachable();
 }

programs/threads.h

@@ -26,7 +26,11 @@ char* itoa(int value, char* str, int base);
 
 int thread(void* args);
 
-__attribute__((naked)) struct optional_int spawn(int (*target)(void*), void* args) {
+// ignore unused parameter errors only for these functions
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunused-parameter"
+__attribute__((naked)) struct optional_int spawn(int (*target)(void*), void* args)
+{
     __asm__ (
          "li a7, 1\n"
          "ecall\n"
@@ -35,7 +39,8 @@ __attribute__((naked)) struct optional_int spawn(int (*target)(void*), void* arg
     __builtin_unreachable();
 }
 
-__attribute__((naked)) struct optional_int join(int pid, int timeout) {
+__attribute__((naked)) struct optional_int join(int pid, int timeout)
+{
     __asm__ (
          "li a7, 3\n"
          "ecall\n"
@@ -45,7 +50,8 @@ __attribute__((naked)) struct optional_int join(int pid, int timeout) {
 }
 
 
-__attribute__((naked)) struct optional_int sleep(int timeout) {
+__attribute__((naked)) struct optional_int sleep(int timeout)
+{
     __asm__ (
          "li a7, 2\n"
          "ecall\n"
@@ -53,3 +59,4 @@ __attribute__((naked)) struct optional_int sleep(int timeout) {
     );
     __builtin_unreachable();
 }
+#pragma GCC diagnostic pop