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Memory not accessible from GDB when using mps3-an547
Description of problem:
Memory (including variables) is not accessible when connecting to the emulated machine via GDB
Steps to reproduce:
1. Create minimal program `main.c`:
```c
int main(void) {
int myvar = 42;
for(;;)
}
```
2. Compile
```bash
arm-none-eabi-gcc -c -o build/main.o -c -mcpu=cortex-m55 -mfloat-abi=hard -mthumb -funsigned-char -mlittle-endian -O0 -g -std=c11 main.c
```
(ARM startup files and include directories omitted for brevity)
3. Link
```bash
arm-none-eabi-g++ -o build/test.elf build/main.o -mcpu=cortex-m55 -mfloat-abi=hard -mthumb -funsigned-char -mlittle-endian --entry=Reset_Handler -static -T./platform.ld -O0 -g
```
(ARM startup files omitted for brevity)
4. Run binary in QEMU:
```bash
qemu-system-arm --machine mps3-an547 -serial mon:stdio -kernel test.elf -gdb tcp::1234 -S
```
5. Attach using GDB `arm-none-eabi-gdb build/test.elf` and set break point to infinite loop
```gdb
target remote :1234
break main.c:18
continue
print myvar
```
Expected Output: 42
Actual Output: `Cannot access memory at address 0x11fffe4`
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