Why does newlib memcpy branch to unused flash location?

0
votes

I'm trying to compile a simple project for a TM4C123GXL microcontroller using arm-none-eabi-gcc. Inside main I call memcpy just to test that it works as expected, but it causes a fault. Inside the disassembly of memcpy one of the first instructions is b.n 0xc7a, which takes the CPU to some unused segment of flash. It's as though memcpy expects some other function to be at that location, but I can't figure out why that would be an issue. It compiles without any warnings or errors.

Here is the Makefile I'm using:

PROJECT = main
SRCS = $(wildcard src/*.c)
OBJ = obj/
OBJS = $(addprefix $(OBJ), $(notdir $(SRCS:.c=.o)))
INC = inc/
LD_SCRIPT = TM4C123GH6PM.ld

CC = arm-none-eabi-gcc
LD = arm-none-eabi-ld 
OBJCOPY = arm-none-eabi-objcopy
RM = rm -rf
MKDIR = @mkdir -p $(@D)

CFLAGS = -ggdb3 -mthumb -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 
CFLAGS += -mfloat-abi=softfp -MD -std=c99 -c -Wextra -Wall -Wno-missing-braces

all: bin/$(PROJECT).elf


$(OBJ)%.o: src/%.c          
    $(MKDIR)              
    $(CC) -o $@ $^ -I$(INC) $(CFLAGS)
    
bin/$(PROJECT).elf: $(OBJS) 
    $(MKDIR)           
    $(CC) -o $@ $^ -Wl,-T $(LD_SCRIPT) -Wl,-e Reset_Handler
    $(OBJCOPY) -O binary $@ bin/$(PROJECT).bin 

clean:
    -$(RM) obj
    -$(RM) bin

And my main:

#include <stdint.h>
#include <string.h>

int main(void){
    uint8_t x[] = {1,2,3};
    uint8_t y[] = {0,0,0};

    uint8_t *xptr = x;
    uint8_t *yptr = y;
    memcpy(yptr, xptr, 3);

    while (1)
        ;
}

And my Reset_Handler, for good measure:

void Reset_Handler(void)
{

    int *src, *dest;

    /* copying of the .data values into RAM */

    src = &_etext;
    for (dest = &_data; dest < &_edata;)
    {
    *dest++ = *src++;
    }

    /* initializing .bss values to zero*/

    for (dest = &__bss_start__; dest < &__bss_end__;)
    {
    *dest++ = 0;
    }

    main();
}

Is there something else I need to do in order to use Newlib's standard C library?

cbare-metalnewlib