Re: Role of qemu-arm

[Philippe Mathieu-Daudé]

Hi Vincent,

On 6/22/20 10:57 AM, Alex Bennée wrote:
> 
> vincent Dupaquis <v.dupaquis@trusted-objects.com> writes:
> 
>> Hello,
>>
>>     I am using qemu for doing simulations of code, and currently find
>> qemu-system-arm convienient.
>>
>>     But, I cannot understand how to use qemu-arm. In fact, what I am
>> searching for is a way of simulating only the ARM core, not any
>> peripherals.

You can start a machine with only a CPU core using:

$ qemu-system-arm -M none -cpu cortex-r5

The core will start running at full speed looping taking
exception because there is no memory on its bus to fetch
the code to run:

$ qemu-system-arm -M none -cpu cortex-r5 -d mmu,int
PMSA MPU lookup for execute at 0x00000000 mmu_idx 33 -> Hit (prot rwx)
Taking exception 3 [Prefetch Abort]
...from EL1 to EL1
...with ESR 0x21/0x8600003f
...with IFSR 0x8 IFAR 0x0
Taking exception 3 [Prefetch Abort]
...from EL1 to EL1
...with ESR 0x21/0x8600003f
...with IFSR 0x8 IFAR 0xc

You can use the '-m <size_mb>' option to add memory (mapped
at the 0x00000000 address).

You can use the '-S' flag to start QEMU with the cores not
running.

Example of use is via gdbstub, filling some instructions in
memory, set $sp and $pc and singlestep.

You can also use the 'loader' device to load a file into
memory (it can understand ELF/hex format, see
docs/generic-loader.txt).

Finally I also recommend you the -semihosting option.

For example you can run an RTOS Fibonacci test displaying
progress via semihosting calls, by using something like
(mapping 2MB of DRAM at 0x0):

$ qemu-system-arm -M none \
  -m 2 \
  -cpu cortex-r5 -d in_asm \
  -semihosting-config enable=on \
  -device loader,file=fibonacci.elf

> 
> There are two modes:
> 
>   - system emulation (CPU + board and peripherals)
>   - linux-user (CPU but with a Linux syscall interface)
> 
>> I can work with qemu-system-arm, and could not find a way
>> to use qemu-arm.
> 
> If you are installing via your distros package manager you probably want
> a package called qemu-user. You can build the only the user-mode
> packages by issuing --disable-system to the configure script.
> 
> The closest thing to being a "pure" just the CPU is probably a
> standalone usermode binary that uses semihosting calls rather than a
> libc/syscall interface.
> 
>>
>>     Would anyone have any pointers to a documentation or a tutorial
>> using this tool ?
>>
>>     Best regards,
>>
>>         Vincent.
> 
>