After reading this question Why is %cl the only register the sal-operation will accept as a parameter?, I'm curious about what other instructions require the count register?
Loop Control
The LOOP instructions assume that the CX, ECX, or RCX register contains the loop count.
loop
loopnz
loopne
loopz
loope
Jumps
Jump instructions that perform a jump if the CX, ECX, or RCX register is zero.
jcxz
jecxz
jrcxz
Repeat Prefixes
These repeat prefixes are used with string instructions and use the count register.
rep
repe
repz
repne
repnz
Bit Shifting
Logical, Shift, Rotate and Bit Instructions (omitted dword and qword variants such as shld, shlq, ...)
shl
shr
sal
sar
rol
ror
rcl
rcr
Fastcall Calling Convention
The first two DWORD or smaller arguments that are found in the argument list from left to right are passed in ECX and EDX registers; all other arguments are passed on the stack from right to left.
__attribute__((fastcall)) void printnums(int num1, int num2, int num3){
printf("The numbers you sent are: %d %d %d", num1, num2, num3);
}
int main(){
printnums(1, 2, 3);
return 0;
}
Microsoft x64 calling convention
In the Microsoft x64 calling convention, the first four integer or pointer arguments are passed to a function in the RCX, RDX, R8, and R9 registers. If there are more than four arguments, the remaining arguments are passed on the stack.
System V AMD64 ABI
The first six integer or pointer arguments are passed in registers RDI, RSI, RDX, RCX, R8, R9.
Question
Are there other scenarios which require the use of the counter register?
Would the best place to check be the Combined Volume Set of Intel® 64 and IA-32 Architectures Software Developer’s Manuals?
