gcc, arm, and thumbs mode

[Anton Kozlov]

Hi Thomas,

On 5/27/22 16:12, Thomas Stüfe wrote:
> P.S. I found one possible solution for my particular problem was to add
> `.type function` to the static assembler routine. That caused gcc to use
> the correct jump instruction (blx instead of bl). But I am not sure this is
> the best solution, maybe best would be to just use the same mode for all
> hotspot compilation units.

AFAIR, that .type %function directive is a correct way to write asm 
code. At least this is what gcc generates for the C code [1]. I'm not 
sure how the annotation in the assembly code affects the caller code, 
may be link time optimization? But if adding the directive resolves the 
issue, I vote for it.

(I expect arm-none crosscompiler to produce similar results compared to 
arm-linux target)

Thanks,
Anton

$ echo "int main() { return 0; }" | arm-none-eabi-gcc -mthumb -S -x c - -o -
	.cpu arm7tdmi
	.arch armv4t
	.fpu softvfp
	.eabi_attribute 20, 1
	.eabi_attribute 21, 1
	.eabi_attribute 23, 3
	.eabi_attribute 24, 1
	.eabi_attribute 25, 1
	.eabi_attribute 26, 1
	.eabi_attribute 30, 6
	.eabi_attribute 34, 0
	.eabi_attribute 18, 4
	.file	"<stdin>"
	.text
	.align	1
	.global	main
	.syntax unified
	.code	16
	.thumb_func
	.type	main, %function
main:
	@ Function supports interworking.
	@ args = 0, pretend = 0, frame = 0
	@ frame_needed = 1, uses_anonymous_args = 0
	push	{r7, lr}
	add	r7, sp, #0
	movs	r3, #0
	movs	r0, r3
	mov	sp, r7
	@ sp needed
	pop	{r7}
	pop	{r1}
	bx	r1
	.size	main, .-main
	.ident	"GCC: (Arch Repository) 12.1.0"