MDB provides facilities to examine the stacks and registers of each thread associated
with the target. The persistent thread variable contains the current representative thread identifier.
The format of the thread identifier depends on the target. The ::regs and
::fpregs dcmds can be used to examine the register set of
the representative thread, or of another thread if its register set is currently
available. In addition, the register set of the representative thread is exported as
a set of named variables. The user can modify the value of
one or more registers by applying the > dcmd to the corresponding named
The MDB kernel target exports the virtual address of the corresponding internal thread
structure as the identifier for a given thread. This address corresponds to the
kthread_t data structure in the operating system source code. When using kmdb, the
CPU identifier for the CPU running kmdb is stored in the cpuid variable.
The MDB process target provides proper support for examination of multi-threaded user processes
that use the native lwp_* interfaces, /usr/lib/libthread.so, or /usr/lib/libpthread.so. When debugging a live
user process, MDB will detect if a single threaded process dlopens or closes
libthread and will automatically adjust its view of the threading model on-the-fly.
The process target thread identifiers will correspond to either the lwpid_t, thread_t, or pthread_t
of the representative, depending on the threading model used by the application.
If MDB is debugging a user process target and the target makes
use of compiler-supported thread-local storage, MDB will automatically evaluate symbol names referring to thread-local
storage to the address of the storage corresponding to the current representative thread.
The ::tls built-in dcmd can be used to display the value of the
symbol for threads other than the representative thread.