[Qemu-devel] qtest protocol: should memset/read/write etc of a size of 0 bytes be permitted?

[Peter Maydell]

I've upgraded to a more recent version of clang, which now produces
undefined-behaviour warnings for passing NULL pointers to some library
functions. One of the things it has shown up is that some of the
qtest tests ask for "memset" with size zero. In our current implementation
this results in qtest.c calling g_malloc(0), which returns NULL, and
then calling memset(NULL, chr, 0), which is UB.

So should we:
(1) declare the qtest protocol commands 'memset', 'read', 'write'
etc which operate on a lump of guest memory of specified size to
support size == 0 as meaning "do nothing"
(2) declare that size == 0 is not valid and make it return a failure
code back down the qtest pipe (and fix the offending tests)

?

The offending tests are i386/ahci/flush/simple and i386/ahci/max
(because ahci_io() calls qmemset() with a zero size.)

thanks
-- PMM