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#Writing assembly in C (simple example)
unique yachtBOT
sturdy quiver
What do I need to change here?
rapid hornet
Didn't you have it working in #c-help-text minutes ago?
sturdy quiver
you can't move a 64-bit register into a 32-bit variable
The system time should be a 32-bit register anyway.
How do I use a 32-bit register instead?
dawn bridge
if you expect the return value to be 32-bits then use eax, not rax
sturdy quiver
Ah!
unique yachtBOT
@sturdy quiver
sturdy quiver
;compile
#include <stdio.h>
#include <time.h>
#include <stdint.h>
typedef uint32_t u32;
u32 get_system_time() {
u32 system_time;
__asm__
(
"mov $201, %%eax;"
"xor %%rdi, %%rdi;"
"syscall;"
"mov %%eax, %0"
: "=r"(system_time)
:
: "%eax", "%rdi"
);
return system_time;
}
int main() {
u32 system_time = get_system_time();
printf("Current time ASM: %llu\n", system_time);
printf("Current time TIME.H: %u\n", (unsigned)time(NULL));
return 0;
}
wanton pondBOT
sturdy quiver
There we go.
main blaze
The system time should be a 32-bit register anyway.
time_t is probably going to be 64 bits
so you are potentially truncating the value
sturdy quiver
time_t is probably going to be 64 bits
I have never seen a unix timestamp to be larger than 32 bits.
In fact that is why we have the "Year 2038" problem
rapid hornet
I have never seen a unix timestamp to be larger than 32 bits.
Could it be larger though? What does the standard say?
main blaze
;compile ```c
#include <time.h>
#include <stdio.h>
printf("%zu", sizeof(time_t));