dtrace: Fix a kernel panic in printm()
When using printm(), one should always pass a scratch pointer to it.
This is achieved by calling printm with memref
BEGIN { printm(fixed_len, memref(ptr, var_len)); }
which will return a pointer to the DTrace scratch space of size
sizeof(uintptr_t) * 2. However, one can easily call printm() as follows
BEGIN { printm(10, (void *)NULL); }
and panic the kernel as a result. This commit does two things:
(1) adds a new macro DTRACE_INSCRATCHPTR(mstate, ptr, howmany) which checks if a certain pointer is in the DTrace scratch space; (2) uses DTRACE_INSCRATCHPTR() to implement a check on printm()'s DIFO return value in order to avoid the panic and sets CPU_DTRACE_BADADDR if the address is not in the scratch space.
Reviewed by: markj
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D41722
(cherry picked from commit 8527bb2aee6ca9013c34445de88217a954b6628d)