38.16.1.5. Magic failure string
We do not know of any way to set the emulator exit status in QEMU arm full system.
For other arch / emulator combinations, we know how to do it:
-
aarch64: aarch64 semihosting supports exit status
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gem5: m5 fail works on all archs
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user mode: QEMU forwards exit status, for gem5 we do some log parsing as described at: Section 11.7.2, “gem5 syscall emulation exit status”
Since we can’t do it for QEMU arm, the only reliable solution is to just parse the guest serial output for a magic failure string to check if tests failed.
Our run scripts parse the serial output looking for a line line containing only exactly the magic regular expression:
lkmc_exit_status_(\d+)
and then exit with the given regular expression, e.g.:
./run --arch aarch64 baremetal/return2.c echo $?
should output:
2
This magic output string is notably generated by:
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rootfs_overlay/lkmc/test_fail.sh, which is used by Test userland in full system
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the
exit()baremetal function whenstatus != 1.Unfortunately the only way we found to set this up was with
on_exit: https://github.com/cirosantilli/linux-kernel-module-cheat/issues/59.Trying to patch
_exitdirectly fails since at that point some de-initialization has already happened which prevents the print.So setup this
on_exitautomatically from all our Baremetal bootloaders, so it just works automatically for the examples that use the bootloaders: https://stackoverflow.com/questions/44097610/pass-parameter-to-atexit/49659697#49659697The following examples end up testing that our setup is working:
Beware that on Linux kernel simulations, you cannot even echo that string from userland, since userland stdout shows up on the serial.