device: 0.816
semantic: 0.785
instruction: 0.772
other: 0.731
graphic: 0.697
boot: 0.638
network: 0.615
socket: 0.601
vnc: 0.545
KVM: 0.462
mistranslation: 0.440
assembly: 0.134

qemu-user warnings confuse userland applications

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.

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).


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