[FR] Suggest adding support for later 64-bit #1
Description
The book suggests that it might cover 64-bit coding (later) so I created two testing platforms on a Raspberry Pi 4B with 4GB RAM:
- Raspbian Buster Lite 2019-09-26 (32-bit)
- Ubuntu Server 19.10 64-bit
I made an attempt to use any of your Chapter 1 code for the 64-bit environment and it of course failed badly.
For your 2nd edition of the book I might suggest the following. The assumption would be that you cover 64-bit and to incorporate it in such a way that the transition is easier with the same scripts.
build
#!/bin/sh
# (This test should be modified to allow the Pi Zero's armv6l to be seen as 32-bit)
if uname -snrvm | grep -q armv7l; then
echo "32-bit detected"
BITS=32
else
echo "64-bit detected"
BITS=64
fi
as -o helloworld.o helloworld-$BITS.s
ld -o bin/helloworld helloworld.o
Next, I would rename all the *.s files to *-32.s in your existing code.
helloworld-32.s
.section .text
.global _start
_start:
mov r0, #1
ldr r1, =helloworld
mov r2, #13
mov r7, #0x04
svc 0
mov r0, #0x0
mov r7, #1
svc 0
.section .data
helloworld: .ascii "Hello World!\n"
helloworld-64.s
.section .text
.global _start
_start:
mov x0, #1
ldr x1, =helloworld
mov x2, #13
mov x8, #0x40
svc 0
mov x0, #0x0
mov x8, #93
svc 0
.section .data
helloworld: .ascii "Hello World!\n"