diff --git a/src/perror.asm b/src/perror.asm
index d3bab51..08957ee 100644
--- a/src/perror.asm
+++ b/src/perror.asm
@@ -166,9 +166,11 @@ section .text
 ;	rdi*	(arg) Pointer to str[] or 0 (no custom message)
 ;	rdx*	Used for syscall NR_write
 ;	r8*	(Re)stores pointer to str[]// Stores address of errMsgUser for cmov
-;	r9*	(Re)stores error code 
+;	r9*	(Re)stores positive error code
 ;	r10*	(Re)stores pointer to error msg
 perror:
+	sub	rsp, SIZE_QWORD
+	push	rax
 	test	rax, rax
 	jz	.quit
 	js	.negErr
@@ -212,4 +214,6 @@ perror:
 	syscall
 	mov	rax, r9
 	.quit:
+	pop	rax
+	add	rsp, SIZE_QWORD
 	ret
diff --git a/src/tests.asm b/src/tests.asm
index eb88cda..dafadc5 100644
--- a/src/tests.asm
+++ b/src/tests.asm
@@ -94,6 +94,9 @@ section .rodata
 	;;;
 	TESTS_PRINT_ALL_OUTPUTS	equ	0 ;If set to 0, only print expected/got and FAIL if failed. Otherwise always print outputs.
 					  ;Note: when set to 0, tests are silent (ie it prints the current test and does not print any output, not even OK)
+
+	;perror.asm
+	TEST_perror		equ	1
 	;core.asm
 	TEST_islower		equ	1
 	TEST_isupper		equ	1
@@ -142,6 +145,16 @@ section .rodata
 	;;;
 	;;; Specific test data
 	;;;
+	;perror()
+	addTestHeader(_perror, "perror")
+	addTest(perror_noerr, "perror() ;rax=0")
+	addTest(perror_einval1, "perror() ;rax=EINVAL")
+	addTest(perror_einval2, "perror('Test') ;rax=EINVAL")
+	addTest(perror_einval3, "perror() ;rax=-EINVAL")
+	addTest(perror_einval4, "perror('Test') ;rax=-EINVAL")
+	addTest(perror_invalid1, "perror() ;rax=999")
+	addTest(perror_invalid2, "perror('Test') ;rax=-999")
+	perrorStr		db	"Test",EOS
 	;islower()
 	addTestHeader(_islower, "islower")
 	addTest(islower_d, "islower('d')")
@@ -219,6 +232,8 @@ section .rodata
 	printfStr1	db	"H%ell%0 T\\%t\he%%%re%\n",EOS
 	addTest(printf_hexpadd, "printf(''%x | %16x | %016x | %#16x | %#016x\n%X | %016X | %16X | %#016X | %#16X\n'', 80181775710, [... same arg 9 more times])")
 	printfStr2	db	"%x | %16x | %016x | %#16x | %#016x\n%X | %016X | %16X | %#016X | %#16X\n",EOS
+	addTest(printf_ppadd, "printf(''%p | %16p | %016p | %#16p | %#016p\n%p | %016p | %16p | %#016p | %#16p\n'', 80181775710, [... same arg 9 more times])")
+	printfStr3	db	"%p | %16p | %016p | %#16p | %#016p\n%p | %016p | %16p | %#016p | %#16p\n",EOS
 
 section .data
 
@@ -230,6 +245,60 @@ _start:
 	xor	r13, r13 ;total tests
 	xor	r14, r14 ;OK tests (assert => true)
 
+;--- perror()
+%if TEST_perror
+	printTestHeader(_perror)
+
+	; TEST 1: perror() ;rax=0
+	printTest(perror_noerr)
+	xor	rax, rax
+	xor	rdi, rdi
+	call	perror
+	assert_eq(0)
+
+	; TEST 2: perror() ;rax=EINVAL
+	printTest(perror_einval1)
+	mov	rax, EINVAL
+	xor	rdi, rdi
+	call	perror
+	assert_eq(EINVAL)
+
+	; TEST 3: perror('Test') ;rax=EINVAL
+	printTest(perror_einval2)
+	mov	rax, EINVAL
+	lea	rdi, [rel perrorStr]
+	call	perror
+	assert_eq(EINVAL)
+
+	; TEST 4: perror() ;rax=-EINVAL
+	printTest(perror_einval3)
+	mov	rax, -EINVAL
+	xor	rdi, rdi
+	call	perror
+	assert_eq(-EINVAL)
+
+	; TEST 5: perror('Test') ;rax=-EINVAL
+	printTest(perror_einval4)
+	mov	rax, -EINVAL
+	lea	rdi, [rel perrorStr]
+	call	perror
+	assert_eq(-EINVAL)
+
+	; TEST 6: perror() ;rax=999
+	printTest(perror_invalid1)
+	mov	rax, 999
+	xor	rdi, rdi
+	call	perror
+	assert_eq(999)
+
+	; TEST 7: perror('Test') ;rax=-999
+	printTest(perror_invalid2)
+	mov	rax, -999
+	xor	rdi, rdi
+	call	perror
+	assert_eq(-999)
+%endif
+
 ;--- islower()
 %if TEST_islower
 	printTestHeader(_islower)
@@ -590,6 +659,23 @@ _start:
 	call	printf
 	add	rsp, SIZE_QWORD * 5
 	assert_eq(174) ;8*16(%[#][0]16(x|X)) + (8*3( | ) + 20 (2x %x) + 2 (NL) => 174
+
+	; TEST 3 (print hexadecimal numbers in multiple possible ways, but using %p)
+	printTest(printf_ppadd)
+	lea	rdi, [rel printfStr3]
+	mov	rsi, 80181775710
+	mov	rdx, rsi
+	mov	rcx, rsi
+	mov	r8, rsi
+	mov	r9, rsi
+	push	rsi
+	push	rsi
+	push	rsi
+	push	rsi
+	push	rsi
+	call	printf
+	add	rsp, SIZE_QWORD * 5
+	assert_eq(178) ;Len of TEST 2 + 4 (since %p always uses prefix 0x, this test has that two times extra => 4 chars)
 %endif
 
 ;;;