I am getting Access violation writing location 0xB7066CBC while running this code.Unable to figure out whats going on, any suggestions?
int main(void)
{
unsigned int SIG = 0x00000000;
unsigned int *base = (unsigned int *)0xb7066CBC;
SIG = 0x5a5a5a5a;
memcpy(base ,&SIG, 4);
}
Here are the values I am getting when I encounter this failure.
&SIG 0x003bf7c0 {0x5a5a5a5a}
SIG 0x5a5a5a5a
base 0xb7066cbc {???}
I am getting Access violation writing location 0xB7066CBC while running this code.Unable to figure out whats going on
What's going on is that the 4 bytes at location 0xB7066CBC are not writable.
Your problem most likely lies in whatever reasoning led you to believe that these bytes are (or should be) writable, but since you didn't provide any clue as to what that reasoning might be, it's hard to offer any help.
Related
This MIPS simulator will read in a text file consisting of LC3100 machine code instructions (represented as decimal values), and execute the program, then display the values of register files and memory after each instruction is completed.
I do not understand how this can be done and simply need a format for what steps I need to take in order to create the simulator in MIPS. Do I write code in C++ or write the code in MIPS? How do I read files if it is in MIPS? Honestly, just confused.
I do not know where I need to start from. This is what I am asking to help figure out.
I'd imagine you'd want to create some global variables that represent your registers and memory:
int memory[0x80000000/4];
int reg_v0;
int reg_t0;
int* reg_pc;
// etc
And then define some functions that mimic the way MIPS behaves. You'll need to read up on how the CPU operates (which is why this example function may seem arbitrary but really it isn't.)
void MIPS_multu(int regA, int regB)
{
// void because we're writing to global variables.
uint64_t temp = regA * regB;
reg_hi = temp >> 32;
reg_lo = (temp & 0x00000000FFFFFFFF);
}
Finally, you'll need to understand how MIPS instructions are encoded and create a routine that can unpack them and select the correct function.
int memory[0x80000000/4];
int reg_v0;
int reg_t0;
int* reg_pc;
// etc
int main()
{
reg_pc = &memory[0];
while (reg_pc < &memory[0x80000000/4])
// chances are this is either invalid C or just bad practice,
// but I can't think of a better way to express the idea
{
int temp = *reg_pc;
// use bitwise operators etc to figure out what the instruction represents,
// and switch cases to pick the functions.
reg_pc++;
}
}
As anything with CUDA, the most basic things are sometimes the hardest...
So...I just want to copy a variable from the CPU to a GPU's constant variable, and I am having a hard time.
This is what i have:
__constant__ int contadorlinhasx_d;
int main(){
(...)
int contadorlinhasx=100;
status=cudaMemcpyToSymbol(contadorlinhasx_d,contadorlinhasx,1*sizeof(int),0,cudaMemcpyHostToDevice);
And i get this error
presortx.cu(222): error: no instance of overloaded function "cudaMemcpyToSymbol" matches the argument list
argument types are: (int, int, unsigned long, int, cudaMemcpyKind)
Could anyone help me? I know it is some stupid error, but I am tired of googling it, and I have spent almost 30 minutes just trying to copy a stupid variable :/
Thanks in advance
You need to do something like
cudaMemcpyToSymbol("contadorlinhasx_d",
&contadorlinhasx,
1*sizeof(int),
0,
cudaMemcpyHostToDevice);
[Note this is the old API call, now deprecated in CUDA 4.0 and newer]
or
cudaMemcpyToSymbol(contadorlinhasx_d,
&contadorlinhasx,
1*sizeof(int),
0,
cudaMemcpyHostToDevice);
If you look at the API documentation, the first two arguments are pointers. The first can either be a string, which will force a symbol lookup internally in the API (pre CUDA 4), or a device symbol address (CUDA 4 and later). The second argument is the address of the host source memory for the copy. The compiler error message is pretty explicit - you are passing the wrong types of argument and the compiler can't find an instance in the library which matches.
I got an "unaligned memory accesses not supported error" and did a Google search for that
but there were no clear explanations.
The whole error message is:
/c:\cuda\include\math_functions_dbl_ptx1.h(1308): Error: Unaligned memory accesses not supported
The following code caused the error:
for (j = low; j <= high; j++)
The variables j and high are declared as int.
This kind of error was encountered before but resolved by itself (I did nothing).
Can anybody explain about this matter?
Theory
On many machines - but not Intel IA32 ones or their relatives - if you want to access a 2-byte quantity (integer), the address must be even, not odd; if you want to access a 4-byte quantity (integer or float) the address must be a multiple of 4 bytes; if you want to access an 8-byte quantity (integer or double), the address must be a multiple of 8 bytes; and so on.
Superficially, then, you have somehow got your code trying dereference a pointer which has bits set in the low-order parts when you should not. For example, one way of forcing the issue (in C) would be:
long l = 0x12345678;
void *v = (char *)&l + 1;
long *lp = v;
l = *lp;
By the time you've gone through the pointer arithmetic, the address in lp is not 4-byte (or 8-byte) aligned; it is off-by-one because of the +1. The last line would give an unaligned memory access pointer.
Practice
Since you have not shown the declarations for your code, we can't be sure what causes the trouble (though you do say j and high are int variables; no comment about low). Indeed, almost independent of the declarations, it seems unlikely that the quoted for loop is the source of the trouble. It may be code close to that, but it probably is not that line.
There is a chance that you have a buffer over-writing problem somewhere and are modifying a pointer by accident, and that modified pointer generates the error. But, since that line does not seem to include any pointers, it is unlikely to be that line that is actually triggering the trouble.
hi i'm working on a personal project
for a transport parser.
i want to be able to represent a recived packet in binary number and afterwards be able to set specific bits.
I've got a pretty good idea how to do the second part but i'm really stuck at the beginning
ive got an advice to use unsigned char for that but can i really represent a full packet in that variable.
thanks
an unsigned char array is probably what you need: you can store whatever you want in this structure and access it in whatever means pleases you.
You could have this container in a bigger container too: the bigger container would have pointers to the each layer's beginning & end etc.
I'd probably have a simple class (simple to begin with anyway):
class Packet
{
public:
Packet(unsigned int length);
Packet(void *data);
bool getBit(unsigned int bit);
void setBit(unsigned int bit,bool set);
private:
std::vector<unsigned char> bytes;
};
That's just to start, no doubt it would get more complex depending what you use it for. You might consider overloading the array operator but that's probably outside "beginner level" and maybe best ignored right now.
I haven't written C in quite some time and am writing an app using the MySQL C API, compiling in g++ on redhat.
So i start outputting some fields with printfs... using the oracle api, with PRO*C, which i used to use (on suse, years ago), i could select an int and output it as:
int some_int;
printf("%i",some_int);
I tried to do that with mysql ints and i got 8 random numbers displayed... i thought this was a mysql api issue and some config issue with my server, and i wasted a few hours trying to fix it, but couldn't, and found that i could do:
int some_int;
printf("%s",some_int);
and it would print out the integer properly. Because i'm not doing computations on the values i am extracting, i thought this an okay solution.
UNTIL I TRIED TO COUNT SOME THINGS....
I did a simple:
int rowcount;
for([stmt]){
rowcount++;
}
printf("%i",rowcount);
i am getting an 8 digit random number again... i couldn't figure out what the deal is with ints on this machine.
then i realized that if i initialize the int to zero, then i get a proper number.
can someone please explain to me under what conditions you need to initialize int variables to zero? i don't recall doing this every time in my old codebase, and i didn't see it in the example that i was modeling my mysql_stmt code from...
is there something i'm missing? also, it's entirely possible i've forgotten this is required each time
thanks...
If you don't initialize your variables, there's no guarantee of a default 0/NULL/whatever value. Some compilers MIGHT initialize it to 0 for you (IIRC, MSVC++ 6.0 would be kind enough to do so), and others might not. So don't rely on it. Never use a variable without first giving it some sort of sane value.
Only global and static values will be initialized to zero. The variables on the stack will always contain garbage value if not initialized.
int g_var; //This is a global varibale. So, initialized to zero
int main()
{
int s_var = 0; //This is on stack. So, you need to explicitly initialize
static int stat_var; //This is a static variable, So, initialized to zero
}
You always neet to initialize your variables. To catch this sort of error, you should probably compile with -Wall to give you all warnings that g++ can provide. I also prefer to use -Werror to make all warnings errors, since it's almost always the case that a warning indicates an error or a potential error and that cleaning up the code is better than leaving it as is.
Also, in your second printf, you used %s which is for printing strings, not integers.
int i = 0;
printf("%d\n", i);
// or
printf("%i\n", i);
Is what you want.
Variable are not automatically initialized in c.
You have indeed forgotten. In C and C++, you don't get any automatic initialization; the contents of c after int c; are whatever happens to be at the address referred to by c at the time.
Best practice: initialize at the definition: int c = 0;.
Oh, PS, and take some care that the MySQL int type matches the C int type; I think it does but I'm not positive. It will be, however, both architecture and compiler sensitive, since sizeof(int) isn't the same in all C environments.
Uninitialized variable.
int some_int = 0;