khalil khalil - 1 year ago 75
C++ Question

In-Assembly example for NEON Cortex-A8

I am trying to compile and example sing assembly codes for NEON for cortex A8 to use this binary on BeagleBone Black board (BBB). I use eclipse tool GCC compiler and Assembler listed below,

GCC : arm-linux-gnueabi-gcc

ASSEMBLER : arm-linux-gnueabi-as

The following error occurs in an example and for every example I use I find similar errors

Description Path Resource Location Type
SP not allowed in register list -- `ldmia r12,{r4-r11,r13,lr}' EXAMPLE_NEON line 61, external location: /tmp/ccTXrczs.s C/C++ Problem

the code i used


* neon.c

#include <stdio.h>

__attribute__((aligned (16)))
unsigned short int data1[8];
unsigned short int data2[8];
unsigned short int out[8];

void* neontest_save_buffer[16];

neontest(unsigned short int *a, unsigned short int *b,
unsigned short int* q)
" movw r12, #:lower16:neontest_save_buffer\n\t"
" movt r12, #:upper16:neontest_save_buffer\n\t"
" stmia r12, {r4-r11, r13, lr} @ save registers\n\t"
" vld1.16 {q1}, [r0:128]\n\t"
" vld1.16 {q2}, [r1:128]\n\t"
" vadd.i16 q0, q1, q2\n\t"
" vst1.32 {q0}, [r2:128]\n\t"
" movw r12, #:lower16:neontest_save_buffer\n\t"
" movt r12, #:upper16:neontest_save_buffer\n\t"
" ldmia r12, {r4-r11, r13, lr} @ reload all registers and return\n\t"


int i;

for (i=0; i<8; i++)

neontest(data1, data2, out);

printf("output is: ");
for (i=0; i<7; i++)
printf("%d, ", out[i]);
printf("%d\n", out[i]);


Aif Aif
Answer Source

Seems like you're using Thumb32 mode, in which sp cannot be in the list of registers (from [1]).

Why do you need to save the stack if you're not setting a new one anyway? Just try to remove r13 from the stm block and ldm block.

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