/zephyr-semihost

Primary LanguageC

Zephyr Semihost bug

Describe the bug I'm trying to replace printk with semihosting (for testing), as our (deeply) embedded system does not have a serial port.

During development, I've stumbled upon the following interesting observation:

semihost_open does not work/causes HARD FAULT, unless I introduce some small delay before calling semihost_exec.

So it would look like this:

// zephyr/arch/common/semihost.c
long semihost_open(const char *path, long mode)
{
	struct semihost_open_args args = {.path = path, .mode = mode, .path_len = strlen(path)};

	k_sleep(K_MSEC(1)); // THIS IS ADDED!
	return semihost_exec(SEMIHOST_OPEN, &args);
}

If I don't do this, it results in a Zephyr hard fault when I try to run the test.

  • My target platform: atsamc21n_xpro

To Reproduce

I have set up a repository, for anyone to try to reproduce this issue:

git clone https://github.com/maksimdrachov/zephyr-semihost
cd zephyr-semihost
git clone git@github.com:zephyrproject-rtos/zephyr.git
cd zephyr 
git checkout c22c4fd49f6671079cd9df19d4c22678294be87d 
cd ..
west update

(This will work with atsamc21n_xpro, if you want to test with a different board: don't forget to update scripts/openocd.cfg)

Terminal window #1:

cd ~/zephyr-semihost
./scripts/openocd.cfg

Terminal window #2:

(On the dev board I'm using there is a serial port, this won't be the case on the final product however.)

minicom -D /dev/serial/by-id/usb-Atmel_Corp._EDBG_CMSIS-DAP_ATML2682071800002034-if01

Terminal window #3:

cd ~/zephyr-semihost
west build -b atsamc21n_xpro ./verification/unit
arm-zephyr-eabi-gdb ./build/zephyr/zephyr.elf -batch -ex "tar ext:3333" -ex "load" -ex "run"

Interestingly, it works for the specific commit (c22c4fd49f) I'm using, I tried doing the same with Zephyr on the latest commit (Zephyr v3.4.0-rc2) and got the same HARD FAULT error.

Result without hotfix

Terminal window #1

term-1

Terminal window #2

term-2

Terminal window #3

term-3

Result with hotfix

Terminal window #1

term-1

Terminal window #2

term-2

Terminal window #3

term-3

Expected behavior semihost_open should not require an additional delay when being called.

Impact So far I've found a workaround, however it is probably something that would have to be addressed since it might be pointing at some serious underlying issues.

Environment (please complete the following information):

  • OS: Linux (Ubuntu)
  • Toolchain: zephyr-sdk-0.16.1
  • Commit SHA or Version used: c22c4fd49f (Zephyr, with one change documented above)