mistranslation: 0.925
other: 0.742
semantic: 0.735
device: 0.726
network: 0.676
instruction: 0.559
socket: 0.518
graphic: 0.468
vnc: 0.466
boot: 0.258
KVM: 0.141
assembly: 0.118

qemu: invalid serial port configuration

The tty_serial_init() function sets the port c_oflags as follows:
tty.c_oflag |= OPOST not clearing ONLCR, ONLRET and others.
The result is that the postprocess output is enabled and host translates 0xa (LF) to 0xd 0xa (CR LF) which breaks the binary transmissions on serial port even if you set the port to raw mode (no matters if on host and/or guest).
The issue has been reported 11 years ago on qemu-devel mailing list:
https://lists.nongnu.org/archive/html/qemu-devel/2006-06/msg00196.html
There was also a FreeBSD patch including the fix:
https://lists.freebsd.org/pipermail/freebsd-ports/2006-October/036390.html

I think the correct port configuration is:
tty.c_iflag &= ~(IGNBRK|BRKINT|PARMRK|ISTRIP|INLCR|IGNCR|ICRNL|IXON|IMAXBEL);
tty.c_oflag &= ~OPOST;

In such case the host will perform no output processing and will pass the data as is.
And the guest will be able to configure input/output processing exactly as it wants.

I believe the following bug is related: https://bugs.launchpad.net/qemu/+bug/1407813

Patch has now been committed here:
https://git.qemu.org/?p=qemu.git;a=commitdiff;h=12fb0ac0575df83cec72ec