Comments for Hardwarebug

Comment on Pointer peril by Mans

Mans — Thu, 20 Oct 2011 15:17:46 +0000

Your program prints the difference between two addresses, computation of which is, as you say, undefined. In this particular case, with your compiler, nothing unexpected happens. Undefined behaviour is not required to do anything strange.

Comment on Pointer peril by Alexandre

Alexandre — Thu, 20 Oct 2011 14:41:12 +0000

On my machine, the following function yields the same result with and without -O0 (gcc 4.5.2). According to my understanding of the specs, it relies on the same undefined behaviour. Or do I misunderstand "array objects"?

#include 
#include 

void foo(int* addr_a) {
  int b;
  ptrdiff_t diff = addr_a - &b;
  printf("&a = %p   --- &b = %p\n", addr_a, &b);
  printf("diff = 0x%x\n", diff);
}

int main(void) {
  int a;
  foo(&a);
  return 0;
}

Comment on Pointer peril by Rémi Denis-Courmont

Rémi Denis-Courmont — Tue, 18 Oct 2011 14:14:55 +0000

As far as I know, nothing in the C standard promises that a and b are on a sizeof(int) address boundary. So even without optimizations, you could still have rounding errors ;-) depending on the ABI obviously.

Comment on Pointer peril by Kostya

Kostya — Tue, 18 Oct 2011 07:23:15 +0000

I wonder how many bugs were reported for GCC producing “wrong” code when pointer aliasing is used. Or other things that ignore undefined behaviour.

All world runs on x86 CPUs after all…

Comment on ARM inline asm secrets by Julien

Julien — Tue, 10 May 2011 01:09:07 +0000

This seems fixed in gcc 4.5.

Comment on Shades of black by av500

av500 — Mon, 14 Feb 2011 22:38:07 +0000

46 DC EA …

Comment on Shades of black by Mans

Mans — Mon, 14 Feb 2011 15:48:46 +0000

I ended up getting a Sony VAIO Z1. Go on, ridicule me for paying the Sony tax. You know you’ll enjoy it.

Comment on Shades of black by Johan Andersson

Johan Andersson — Mon, 14 Feb 2011 15:33:46 +0000

What laptop did you buy?

Comment on Shades of black by cartman

cartman — Mon, 14 Feb 2011 15:33:32 +0000

You forgot to mention the brand of your selected laptop. We are wondering…

Comment on ARM inline asm secrets by Julien

Julien — Wed, 29 Dec 2010 04:33:24 +0000

I didn’t know that, thanks! I’m not using any hardcoded clobberlist anymore anyway (except for memory and cc).