add better inline assembler example

pull/589/head
Alexander Kuleshov 6 years ago
parent f3f7cc503c
commit 3c83a2257a
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@ -406,25 +406,29 @@ The result, as expected:
All of these constraints may be combined (so long as they do not conflict). In this case the compiler will choose the best one for a certain situation. For example:
```C
#include <stdio.h>
unsigned long a = 1;
unsigned long a = 10;
unsigned long b = 20;
int main(void)
void main(void)
{
unsigned long b;
__asm__ ("movq %1,%0" : "=r"(b) : "r"(a));
return b;
__asm__ ("movq %1,%0" : "=mr"(b) : "rm"(a));
}
```
will use a memory operand:
```assembly
0000000000400400 <main>:
4004aa: 48 8b 05 6f 0b 20 00 mov 0x200b6f(%rip),%rax # 601020 <a>
main:
movq a(%rip),b(%rip)
ret
b:
.quad 20
a:
.quad 10
```
instead of direct usage of general purpose registers.
That's about all of the commonly used constraints in inline assembly statements. You can find more in the official [documentation](https://gcc.gnu.org/onlinedocs/gcc/Simple-Constraints.html#Simple-Constraints).
Architecture specific constraints

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