Hi William, Thanks for the help. I'm guessing the register keyword doesn't address variables directly or doesn't do what I thought it was doing. I'm a bit new to apple. What I've discovered is in my thread is I have no standard I/O where I'm crashing so I have no print or logging capability. Thus I'm now leaning towards using unused registers to figure out where its crashing. I also don't have a good way to use a debugger afaik unless I could trigger the debugger at crash time. it used to do so but for some reason it isn't doing it now. I have the nvram settings setup to do so but its not triggering. gordo

-------Original Message------- From: William Kucharski <kucharsk@mac.com> To: Gordo Cath <ds@y23.org> Cc: darwin-kernel@lists.apple.com Subject: Re: I'd like to be able to set registers directly Sent: Jul 07 '16 08:56

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On Jul 7, 2016, at 6:36 AM, Gordo Cath <ds@y23.org> wrote:

Hi, I'd like to be able to set a register directly from my c code.  I'm using the llvm compiler in a x86_64 build/run environment.

When I compile and link the following code I get no errors or warnings:

I used the thread_create_running function and during setup set the r11 register to 0xBEAD as a start state using x86_thread_state64_t .

///snippet---- at the very start of my thread I have the following tidbit of code: register uint64_t r11 asm("r11"); r11=0xfade; // some value -- don't care about the value, just want my value set. //end snippet

What, precisely, are you trying to do?  As far as I know, that asm syntax is just wrong.

I would expect to see something like this for x86_64:

#include <stdio.h> #include <sys/types.h>

int main() { int64_t r11;

r11 = 0xc01ddeadbeef; /* init r11 */

asm ("movq %0, %%r11" :: "r"(r11) : "r11"); /* move r11 to %r11 */ r11 = 0; /* zero r11 */ asm ("movq %%r11, %0" : "=r"(r11) ::); /* move %r11 to r11 */

(void) printf("%llx\n", r11); /* verify %r11 */ return 0; }

    William Kucharski

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