qemu-user warnings confuse userland applications

[John Paul Adrian Glaubitz]

I recently observed that warning messages emitted by qemu-user can confuse applications when reading from stdout/stderr. This was observed with the configure script of OpenJDK-11 on qemu-sh4:

configure: Found potential Boot JDK using configure arguments
configure: Potential Boot JDK found at /usr/lib/jvm/java-10-openjdk-sh4 is incorrect JDK version (qemu: Unsupported syscall: 318); ignoring
configure: (Your Boot JDK version must be one of: 10 11)
configure: error: The path given by --with-boot-jdk does not contain a valid Boot JDK
configure exiting with result code 1

See: https://buildd.debian.org/status/fetch.php?pkg=openjdk-11&arch=sh4&ver=11%7E18-1&stamp=1529119043&raw=0

Commenting out the line of code which emits the warning fixes the problem for me and the configure script finishes without problems.

Thus, qemu should be modified to avoid cluttering stdout or stderr with its own messages and rather send those warnings to a log file or similar.

[Peter Maydell (pmaydell)]

Yes, we should probably move these "unimplemented syscall" warnings to the LOG_UNIMP logging level (which you can then turn on if you want them).

[Thomas Huth (th-huth)]

Patch has been merged here:
https://git.qemu.org/?p=qemu.git;a=commitdiff;h=122f9c83f2ef1cd90152