Label

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The label keyword is used for declaration of labels (markers for unconditional jumps using goto keyword) used further in the unit/program.

A label section is also required for jump targets in asm-blocks.

program sumExample(input, output, stderr);

{ iteratively calculates the sum over first n integers }
function iterativeSumFirstNIntegers(const n: longword): qword;
{$ifdef CPUX86_64} // ============= optimized implementation
// assembler modifier appended to routine declaration
assembler;
// you have to familiarize the compiler with symbols
// which are meant to be jump targets
{$goto on}
label
	isfni_iterate;
{$asmMode intel}
asm
	xor rax, rax // rax := 0
	// ecx is used as counter by loop instruction
	mov ecx, n   // ecx := n
isfni_iterate:
	add rax, qword(ecx) // rax := rax + ecx
	loop isfni_iterate  // dec(ecx)
	// if ecx <> 0 then goto isfni_iterate
	
	// the @result macro represents the functions return value
	mov @result, rax // result := rax
// note, a list of modified registers (here ['rax', 'ecx'])
//       is ignored for pure assembler routines
end;
{$else} // ========================== default implementation
var
	i: longword;
	x: qword;
begin
	x := 0; // mov rax, 0
	for i := n downto 1 do // mov ecx, n
	begin
		x := x + i; // add rax, ecx
	end; // loop isfni_iterate
	iterativeSumFirstNIntegers := x; // mov @result, rax
end;
{$endif}

// M A I N =================================================
var
	n: longword;
begin
	readLn(n);
	writeLn(iterativeSumFirstNIntegers(n));
end.

Of course in a production program, you would use an algorithm applying the formula sum := (n * (n + 1)) div 2 (“Gaussian sum formula”).