To support the fasttrap provider from very early in a process's life,
the run-time linker, ld.so.1, has a program header of type PT_SUNWDTRACE
which points to a data object which must be PT_SUNWDTRACE_SIZE bytes.
This structure mimics the fasttrap provider section of the ulwp_t structure.
When the fasttrap provider is changed to require new or different
instructions, the data object in ld.so.1 and the thread initializers in libc
(libc_init() and _thrp_create()) need to be updated to include the new
instructions, and PT_SUNWDTRACE needs to be changed to a new unique number
(while the old value gets assigned something like PT_SUNWDTRACE_1). Since the
linker must be backward compatible with old Solaris releases, it must have
program headers for each of the PT_SUNWDTRACE versions. The kernel's
elfexec() function only has to look for the latest version of the
PT_SUNWDTRACE program header.