diff --git a/src/VM/VM.c b/src/VM/VM.c
index a14b751..2753c6a 100644
--- a/src/VM/VM.c
+++ b/src/VM/VM.c
@@ -6,11 +6,15 @@ void VM_init(VM* vm){
     vm->state = VMState_Initialized;
 }
 
-void VM_setErrorMessage(VM* vm, const char* format, ...){
+void _VM_setError(VM* vm, const char* context, const char* format, ...){
     va_list argv;
+    char position_str[32];
+    sprintf(position_str, "[at 0x%x][", (u32)vm->current_pos);
+    char* real_format = strcat_malloc(position_str, context, "] ", format);
     va_start(argv, format);
-    char* NULLABLE(buf) = vsprintf_malloc(256, format, argv);
+    char* NULLABLE(buf) = vsprintf_malloc(256, real_format, argv);
     va_end(argv);
+    free(real_format);
     if(buf == NULL){
         buf = malloc(16);
         strcpy(buf, "SPRINTF FAILED");
@@ -20,11 +24,11 @@ void VM_setErrorMessage(VM* vm, const char* format, ...){
 
 bool VM_loadProgram(VM* vm, u8* data, size_t size){
     if(data == NULL){
-        VM_setErrorMessage(vm, "[VM_loadProgram] can't load program because data == NULL");
+        VM_setError(vm, "data == NULL");
         return false;
     }
     if(size == 0){
-        VM_setErrorMessage(vm, "[VM_loadProgram] can't load program because size == 0");
+        VM_setError(vm, "size == 0");
         return false;
     }
 
@@ -35,30 +39,30 @@ bool VM_loadProgram(VM* vm, u8* data, size_t size){
 
 i32 VM_executeProgram(VM* vm){
     if(vm->data == NULL){
-        VM_setErrorMessage(vm, "[VM_executeProgram] data is null");
+        VM_setError(vm, "data == null");
         return -1;
     }
 
-    size_t pos = 0;
-    while (pos < vm->data_size){
-        u8 opcode = vm->data[pos];
+    vm->current_pos = 0;
+    while (vm->current_pos < vm->data_size){
+        u8 opcode = vm->data[vm->current_pos];
 
         const Instruction* instr = Instruction_getFromOpcode(opcode);
         if(instr == NULL){
-            VM_setErrorMessage(vm, "[%p] unknown opcode %02x", (void*)pos, opcode);
+            VM_setError(vm, "unknown opcode %02X", opcode);
             return -1;
         }
 
-        pos++;
-        i32 bytes_read = instr->implementation(vm, pos);
+        vm->current_pos++;
+        i32 bytes_read = instr->implementation(vm);
         if(bytes_read < 0)
             return -1;
 
-        pos += bytes_read;
+        vm->current_pos += bytes_read;
     }
 
     if(vm->state != VMState_Exited){
-        VM_setErrorMessage(vm, "[%p] unexpected end of program", (void*)pos);
+        VM_setError(vm, "unexpected end of the program");
         return -1;
     }
 
@@ -68,7 +72,8 @@ i32 VM_executeProgram(VM* vm){
 
 bool VM_dataRead(VM* vm, void* dst, size_t pos, size_t size){
     if(pos + size >= vm->data_size){
-        VM_setErrorMessage(vm, "[%p] unexpected end of data", (void*)vm->data_size);
+        VM_setError(vm, "can't read %lli bytes from 0x%x, because only %lli are avaliable",
+            size, (u32)pos, vm->data_size - size);
         return false;
     }
 
diff --git a/src/VM/VM.h b/src/VM/VM.h
index 149a6c9..865555b 100644
--- a/src/VM/VM.h
+++ b/src/VM/VM.h
@@ -49,6 +49,7 @@ typedef struct VM {
 
     u8* data;
     size_t data_size;
+    size_t current_pos;
 } VM;
 
 void VM_init(VM* vm);
@@ -64,4 +65,5 @@ i32 VM_executeProgram(VM* vm);
 
 bool VM_dataRead(VM* vm, void* dst, size_t pos, size_t size);
 
-void VM_setErrorMessage(VM* vm, const char* format, ...) __attribute__((__format__ (__printf__, 2, 3)));
+#define VM_setError(vm, format, ...) _VM_setError(vm, __func__, format ,##__VA_ARGS__)
+void _VM_setError(VM* vm, const char* context, const char* format, ...) __attribute__((__format__(__printf__, 3, 4)));
diff --git a/src/instructions/impl/EXIT.c b/src/instructions/impl/EXIT.c
index bf1d641..ae95b17 100644
--- a/src/instructions/impl/EXIT.c
+++ b/src/instructions/impl/EXIT.c
@@ -2,7 +2,7 @@
 
 /// EXIT
 /// ax - exit code
-i32 EXIT_impl(VM* vm, size_t pos){
+i32 EXIT_impl(VM* vm){
     vm->state = VMState_Exited;
     return 0;
 }
diff --git a/src/instructions/impl/MOV.c b/src/instructions/impl/MOV.c
index 5149a0e..567421b 100644
--- a/src/instructions/impl/MOV.c
+++ b/src/instructions/impl/MOV.c
@@ -1,13 +1,13 @@
 #include "impl_macros.h"
 
 /// MOV [dst_register] [src_register]
-i32 MOV_impl(VM* vm, size_t pos){
+i32 MOV_impl(VM* vm){
     u8 dst_register_i = 0;
     readRegisterVar(dst_register_i);
     u8  src_register_i = 0;
     readRegisterVar(src_register_i);
     if(dst_register_i == src_register_i){
-        VM_setErrorMessage(vm, "[%p] dst_register_i == src_register_i (%x) ", (void*)pos, src_register_i);
+        VM_setError(vm, "dst_register_i == src_register_i (%x) ", src_register_i);
         return -1;
     }
 
diff --git a/src/instructions/impl/NOP.c b/src/instructions/impl/NOP.c
index 59cbe67..e14facb 100644
--- a/src/instructions/impl/NOP.c
+++ b/src/instructions/impl/NOP.c
@@ -1,6 +1,6 @@
 #include "impl_macros.h"
 
 /// NOP
-i32 NOP_impl(VM* vm, size_t pos){
+i32 NOP_impl(VM* vm){
     return 0;
 }
diff --git a/src/instructions/impl/PUSH.c b/src/instructions/impl/PUSH.c
index ecc2c4a..91c4241 100644
--- a/src/instructions/impl/PUSH.c
+++ b/src/instructions/impl/PUSH.c
@@ -1,14 +1,14 @@
 #include "impl_macros.h"
 
 /// PUSH [dst_register] [value_size] [value]
-i32 PUSH_impl(VM* vm, size_t pos){
+i32 PUSH_impl(VM* vm){
     u8 dst_register_i = 0;
     readRegisterVar(dst_register_i);
     u8 value_size = 0;
     readValueSizeVar(value_size);
     
     vm->registers[dst_register_i].u32v = 0;
-    if(!VM_dataRead(vm, &vm->registers[dst_register_i].u32v, pos, value_size))
+    if(!VM_dataRead(vm, &vm->registers[dst_register_i].u32v, vm->current_pos, value_size))
         return -1;
 
     return sizeof(dst_register_i) + sizeof(value_size) + value_size;
diff --git a/src/instructions/impl/SYS.c b/src/instructions/impl/SYS.c
index 44813ff..3394ad9 100644
--- a/src/instructions/impl/SYS.c
+++ b/src/instructions/impl/SYS.c
@@ -1,13 +1,13 @@
 #include "impl_macros.h"
 
-FILE* NULLABLE(fileFromN)(VM* vm, size_t pos, u32 file_n){
+FILE* NULLABLE(fileFromN)(VM* vm, u32 file_n){
     FILE* f = NULL;
     switch(file_n){
         case 0: f = stdin; break;
         case 1: f = stdout; break;
         case 2: f = stderr; break;
         default:
-            VM_setErrorMessage(vm, "[%p] invalid file_n (%x) ", (void*)pos, file_n);
+            VM_setError(vm, "invalid file_n (%x) ", file_n);
             break;
     }
 
@@ -16,7 +16,7 @@ FILE* NULLABLE(fileFromN)(VM* vm, size_t pos, u32 file_n){
 
 /// SYS
 /// ax - func code
-i32 SYS_impl(VM* vm, size_t pos){
+i32 SYS_impl(VM* vm){
     u8 func_code = vm->ax.u8v0;
     size_t result_code = 0;
     switch(func_code){
@@ -25,17 +25,17 @@ i32 SYS_impl(VM* vm, size_t pos){
         // cx - buffer ptr
         // dx - buffer size
         case 0:;
-            result_code = fread(vm->data + vm->cx.u32v, 1, vm->dx.u32v, fileFromN(vm, pos, vm->bx.u32v));
+            result_code = fread(vm->data + vm->cx.u32v, 1, vm->dx.u32v, fileFromN(vm, vm->bx.u32v));
             break;
         // sys_write
         // bx - file n
         // cx - buffer ptr
         // dx - buffer size
         case 1:;
-            result_code = fwrite(vm->data + vm->cx.u32v, 1, vm->dx.u32v, fileFromN(vm, pos, vm->bx.u32v));
+            result_code = fwrite(vm->data + vm->cx.u32v, 1, vm->dx.u32v, fileFromN(vm, vm->bx.u32v));
             break;
         default:
-            VM_setErrorMessage(vm, "[%p] invalid system call (%x) ", (void*)pos, func_code);
+            VM_setError(vm, "invalid system call (%x) ", func_code);
             return -1;
     }
 
diff --git a/src/instructions/impl/impl_macros.h b/src/instructions/impl/impl_macros.h
index aaef32d..6dd7e1e 100644
--- a/src/instructions/impl/impl_macros.h
+++ b/src/instructions/impl/impl_macros.h
@@ -2,14 +2,14 @@
 #include "../instructions.h"
 
 #define readVar(VAR) {\
-    if(!VM_dataRead(vm, &VAR, pos, sizeof(VAR))) \
+    if(!VM_dataRead(vm, &VAR, vm->current_pos, sizeof(VAR))) \
         return -1;\
-    pos += sizeof(VAR);\
+    vm->current_pos += sizeof(VAR);\
 }
 
 #define validateRegisterIndex(VAR) {\
     if(VAR > sizeof(vm->registers)){\
-        VM_setErrorMessage(vm, "[%p] invalid register index (%x)", (void*)pos, VAR);\
+        VM_setError(vm, "invalid register index (%x)", VAR);\
         return -1;\
     }\
 }
@@ -21,7 +21,7 @@
 
 #define validateValueSize(VAR) {\
     if(VAR < 1 || VAR > 4){\
-        VM_setErrorMessage(vm, "[%p] invalid value_size (%x)", (void*)pos, VAR);\
+        VM_setError(vm, "invalid value_size (%x)", VAR);\
         return -1;\
     }\
 }
diff --git a/src/instructions/impl/math_operators.c b/src/instructions/impl/math_operators.c
index feeb0f0..b39b113 100644
--- a/src/instructions/impl/math_operators.c
+++ b/src/instructions/impl/math_operators.c
@@ -22,26 +22,26 @@
 }
 
 /// ADD [dst_register] [src_register]
-i32 ADD_impl(VM* vm, size_t pos){
+i32 ADD_impl(VM* vm){
     mathOperatorImpl(+);
 }
 
 /// SUB [dst_register] [src_register]
-i32 SUB_impl(VM* vm, size_t pos){
+i32 SUB_impl(VM* vm){
     mathOperatorImpl(-);
 }
 
 /// MUL [dst_register] [src_register]
-i32 MUL_impl(VM* vm, size_t pos){
+i32 MUL_impl(VM* vm){
     mathOperatorImpl(*)
 }
 
 /// DIV [dst_register] [src_register]
-i32 DIV_impl(VM* vm, size_t pos){
+i32 DIV_impl(VM* vm){
     mathOperatorImpl(/)
 }
 
 /// MOD [dst_register] [src_register]
-i32 MOD_impl(VM* vm, size_t pos){
+i32 MOD_impl(VM* vm){
     mathOperatorImpl(%)
 }
diff --git a/src/instructions/instructions.h b/src/instructions/instructions.h
index 67a3760..fc1f693 100644
--- a/src/instructions/instructions.h
+++ b/src/instructions/instructions.h
@@ -3,7 +3,7 @@
 
 ///@param program_pos position in vm->program next afrer opcode
 ///@returns number of bytes read
-typedef i32 (*InstructionImplFunc_t)(VM* vm, size_t program_pos);
+typedef i32 (*InstructionImplFunc_t)(VM* vm);
 
 typedef struct Instruction {
     const char* name;
@@ -20,15 +20,15 @@ typedef struct Instruction {
 /// @return ptr to struct or NULL
 const Instruction* NULLABLE(Instruction_getFromOpcode)(u8 opcode);
 
-i32 NOP_impl(VM* vm, size_t pos);
-i32 PUSH_impl(VM* vm, size_t pos);
-i32 MOV_impl(VM* vm, size_t pos);
-i32 ADD_impl(VM* vm, size_t pos);
-i32 SUB_impl(VM* vm, size_t pos);
-i32 MUL_impl(VM* vm, size_t pos);
-i32 DIV_impl(VM* vm, size_t pos);
-i32 MOD_impl(VM* vm, size_t pos);
-i32 SYS_impl(VM* vm, size_t pos);
-i32 EXIT_impl(VM* vm, size_t pos);
-i32 JMP_impl(VM* vm, size_t pos);
-i32 CALL_impl(VM* vm, size_t pos);
+i32 NOP_impl(VM* vm);
+i32 PUSH_impl(VM* vm);
+i32 MOV_impl(VM* vm);
+i32 ADD_impl(VM* vm);
+i32 SUB_impl(VM* vm);
+i32 MUL_impl(VM* vm);
+i32 DIV_impl(VM* vm);
+i32 MOD_impl(VM* vm);
+i32 SYS_impl(VM* vm);
+i32 EXIT_impl(VM* vm);
+i32 JMP_impl(VM* vm);
+i32 CALL_impl(VM* vm);
diff --git a/src/main.c b/src/main.c
index d916227..01d6411 100644
--- a/src/main.c
+++ b/src/main.c
@@ -19,7 +19,7 @@ i32 main(const i32 argc, const char** argv){
             for(u8 opcode = 0; opcode < 255; opcode++){
                 const Instruction* instr = Instruction_getFromOpcode(opcode);
                 if(instr != NULL){
-                    printf("%02x %s\n", opcode, instr->name);
+                    printf("%02X %s\n", opcode, instr->name);
                 }
             }
             return 0;
@@ -76,6 +76,40 @@ i32 main(const i32 argc, const char** argv){
     return exit_code;
 }
 
+
+char* _strcat_malloc(size_t n, const char* str0, ...){
+    va_list argv;
+    va_start(argv, str0);
+    char* heap_ptr = _vstrcat_malloc(n, str0, argv);
+    va_end(argv);
+    return heap_ptr;
+}
+
+char* _vstrcat_malloc(size_t n, const char* str0, va_list argv){
+    size_t str0_len = strlen(str0);
+    size_t total_len = str0_len;
+    const char** const parts = malloc(sizeof(const char*) * n);
+    size_t* const part_lengths = malloc(sizeof(size_t) * n);
+    for(size_t i = 0; i < n; i++){
+        const char* part = va_arg(argv, const char*);
+        size_t length = strlen(part);
+        parts[i] = part;
+        part_lengths[i] = length;
+        total_len += length;
+    }
+    char* const buf = malloc(total_len + 1);
+    memcpy(buf, str0, str0_len);
+    char* walking_ptr = buf + str0_len;
+    for(size_t i = 0; i < n; i++){
+        memcpy(walking_ptr, parts[i], part_lengths[i]);
+        walking_ptr += part_lengths[i];
+    }
+    buf[total_len] = '\0';
+    free(parts);
+    free(part_lengths);
+    return buf;
+}
+
 char* NULLABLE(sprintf_malloc)(size_t buffer_size, const char* format, ...){
     va_list argv;
     va_start(argv, format);
diff --git a/src/std.h b/src/std.h
index 8296c0b..9f30d40 100644
--- a/src/std.h
+++ b/src/std.h
@@ -24,10 +24,28 @@ typedef u8 bool;
 #define true  1
 #define false 0
 
+#define __count_args( \
+    a0, a1, a2, a3, a4, a5, a6, a7 , a8, a9, a10,a11,a12,a13,a14,a15, \
+    a16,a17,a18,a19,a20,a21,a22,a23, a24,a25,a26,a27,a28,a29,a30,a31, \
+    a32,a33,a34,a35,a36,a37,a38,a39, a40,a41,a42,a43,a44,a45,a46,a47, \
+    a48,a49,a50,a51,a52,a53,a54,a55, a56,a57,a58,a59,a60,a61,a62,a63, \
+    a64,...) a64
+// Macro for counting variadic arguments (max 64)
+// (see usage in kprint.h)
+#define count_args(ARGS...) __count_args(ARGS, \
+    64,63,62,61,60,59,58,57, 56,55,54,53,52,51,50,49, \
+    48,47,46,45,44,43,42,41, 40,39,38,37,36,35,34,33, \
+    32,31,30,29,28,27,26,25, 24,23,22,21,20,19,18,17, \
+    16,15,14,13,12,11,10,9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
+
 #define printfe(FORMAT, ...) fprintf(stderr, FORMAT ,##__VA_ARGS__)
 
 /// @warning pointer can be null
 #define NULLABLE(NAME) NAME
 
-char* NULLABLE(sprintf_malloc)(size_t buffer_size, const char* format, ...) __attribute__((__format__ (__printf__, 2, 3)));
+#define strcat_malloc(STR0, ...) _strcat_malloc(count_args(__VA_ARGS__), STR0, __VA_ARGS__)
+char* _strcat_malloc(size_t n, const char* str0, ...);
+char* _vstrcat_malloc(size_t n, const char* str0, va_list argv);
+
+char* NULLABLE(sprintf_malloc)(size_t buffer_size, const char* format, ...) __attribute__((__format__(__printf__, 2, 3)));
 char* NULLABLE(vsprintf_malloc)(size_t buffer_size, const char* format, va_list argv);