The calling convention deion is incomplete without specifying the alignment of s

Alignment of scalar values should be specified about riscv-elf-psabi-doc HOT 3 CLOSED

riscv-non-isa commented on July 20, 2024

Alignment of scalar values should be specified

from riscv-elf-psabi-doc.

Comments (3)

palmer-dabbelt commented on July 20, 2024

Thanks for going through the documentation, it's great to make sure the LLVM and GCC stuff match before people start really using our stuff. Looks like we're 64-bit aligned for uint64_t on rv32g. @sorear, can you document it?

palmer gamma02 ~ $ cat doublealign.c 
#include <stdint.h>

struct aligntest {
	uint32_t a;
	uint64_t b;
	uint32_t c;
};

void func(void *);

extern struct aligntest aligntest;

int main() {
	func(&aligntest.a);
	func(&aligntest.b);
	func(&aligntest.c);
	return 0;
};
	
	
palmer gamma02 ~ $ riscv64-unknown-linux-gnu-gcc doublealign.c -march=rv32g -mabi=ilp32 -O3 -S -o -
	.file	"doublealign.c"
	.option nopic
	.section	.text.startup,"ax",@progbits
	.align	2
	.globl	main
	.type	main, @function
main:
	lui	a0,%hi(aligntest)
	add	sp,sp,-16
	add	a0,a0,%lo(aligntest)
	sw	ra,12(sp)
	call	func
	lui	a0,%hi(aligntest+8)
	add	a0,a0,%lo(aligntest+8)
	call	func
	lui	a0,%hi(aligntest+16)
	add	a0,a0,%lo(aligntest+16)
	call	func
	lw	ra,12(sp)
	li	a0,0
	add	sp,sp,16
	jr	ra
	.size	main, .-main
	.ident	"GCC: (GNU) 6.1.0"

from riscv-elf-psabi-doc.

asb commented on July 20, 2024

Thanks Palmer, it was actually double fp I was referring to, though I would guess these are 64-bit aligned on RV32 as well (can't ssh into my machine with riscv-gcc to verify right now).

from riscv-elf-psabi-doc.

palmer-dabbelt commented on July 20, 2024

doubles would definitely want to be 64-bit aligned, since there's a fld instruction even on RV32D.

from riscv-elf-psabi-doc.

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