arm32 gcc 'unsigned long long' args passing how to ensure align8bytes on stack? - gcc

Question

using toolchains:
"gcc-arm-none-eabi-9-2020-q2-update"
build cmd:
"arm-none-eabi-gcc -MMD -g -Wno-discarded-qualifiers -O0 -mcpu=cortex-r52 -c -DGCC -mthumb -mfloat-abi=hard -mfpu=fp-armv8 -nostartfiles -ffreestanding -falign-functions=16 -falign-jumps=8 -falign-loops=8 -fomit-frame-pointer -funroll-loops printf.c -o printf.o"
C code:
int _printf(const char *fmt, ...) {
va_list ap;
va_start(ap, fmt);
my_vprintf(fmt, ap);
va_end(ap);
return 0;
}
int printf_test(void) {
_printf("test hex long number = %d %d 0x%lx\n", 123, 321, 0x123456789abcdef0ull);
return 0;
}
static void out_num(long long n, int base, char lead, int maxwidth) {
unsigned long long m = 0;
char buf[MAX_NUMBER_BYTES], *s = buf + sizeof(buf);
int count = 0, i = 0;
*--s = '\0';
if (n < 0 && base == 10) {
m = -n;
} else {
m = n;
}
do {
*--s = hex_tab[m % base];
count++;
} while ((m /= base) != 0);
if( maxwidth && count < maxwidth) {
for (i = maxwidth - count; i; i--) {
*--s = lead;
}
}
if (n < 0 && base == 10) {
*--s = '-';
}
outs(s);
}
asm:
<printf_test>:
b500 push {lr}
b083 sub sp, #12
a30a add r3, pc, #40 ; (adr r3, 4012a0 <printf_test+0x30>)
e9d3 2300 ldrd r2, r3, [r3]
**e9cd 2300 strd r2, r3, [sp]** // save the longlong args into sp
f240 1241 movw r2, #321 ; 0x141
217b movs r1, #123 ; 0x7b
f245 0020 movw r0, #20512 ; 0x5020
f2c0 0040 movt r0, #64 ; 0x40
f7ff ffe0 bl 401250 <_printf>
2300 movs r3, #0
4618 mov r0, r3
b003 add sp, #12
f85d fb04 ldr.w pc, [sp], #4
bf00 nop
f3af 8000 nop.w
9abcdef0 bls ff338e68 <__bss_end+0xfe3f4ba8>
12345678 eorsne r5, r4, #120, 12 ; 0x7800000
f3af 8000 nop.w
f3af 8000 nop.w
<_printf>:
b40f push {r0, r1, r2, r3}
b500 push {lr}
b083 sub sp, #12
**ab05 add r3, sp, #20** // the va_list ap just point to r1 address, the longlong args on sp is missing?
9301 str r3, [sp, #4]
9901 ldr r1, [sp, #4]
9804 ldr r0, [sp, #16]
f7ff fe9f bl 400fa0 <my_vprintf>
2300 movs r3, #0
4618 mov r0, r3
b003 add sp, #12
f85d eb04 ldr.w lr, [sp], #4
b004 add sp, #16
4770 bx lr
when in my_vprintf func, the va_list ap args address is:
0x0000000000F439B8 0000007B 00000141 12345678 9ABCDEF0 {...A...xV4.ðÞ¼.
0x0000000000F439C8 12345678 0000000A 004044D1 00000000 xV4.....ÑD#.....
the result printf is:
test hex long number = 123 321 0x9abcdef012345678
expected is:
test hex long number = 123 321 0x123456789abcdef0
my_vprintf code:
static int my_vprintf(const char *fmt, va_list ap) {
char lead = ' ';
int alignleft = 0;
int maxwidth = 0;
for(; *fmt != '\0'; fmt++) {
if (*fmt != '%') {
outc(*fmt);
continue;
}
lead = ' ';
maxwidth = 0;
//format : %08d, %8d,%d,%u,%x,%f,%c,%s
fmt++;
if (*fmt == '-') {
fmt++;
alignleft = 1;
}
if(*fmt == '0') {
lead = '0';
fmt++;
}
while(*fmt >= '0' && *fmt <= '9') {
maxwidth *= 10;
maxwidth += (*fmt - '0');
fmt++;
}
switch (*fmt) {
case 'd':
out_num(va_arg(ap, int), 10, lead, maxwidth);
break;
case 'o':
out_num(va_arg(ap, unsigned int), 8, lead, maxwidth);
break;
case 'u':
out_num(va_arg(ap, unsigned int), 10, lead, maxwidth);
break;
case 'l':
fmt++;
if (*fmt == 'd') {
out_num(va_arg(ap, long long), 10, lead, maxwidth);
} else if (*fmt == 'u') {
out_num(va_arg(ap, unsigned long long), 10, lead, maxwidth);
} else if (*fmt == 'x' || *fmt == 'X') {
out_num(va_arg(ap, unsigned long long), 16, lead, maxwidth);
}
break;
case 'f':
out_float(va_arg(ap, double), maxwidth);
break;
case 'X':
case 'x':
out_num(va_arg(ap, unsigned int), 16, lead, maxwidth);
break;
case 'c':
outc(va_arg(ap, int));
break;
case 's':
out_str(va_arg(ap, char *), lead, alignleft, maxwidth);
break;
default:
outc(*fmt);
break;
}
}
return 0;
}
It seems that the longlong passing args on stack couldn't complie as expected and deal with appropriately. Why it happened?