Replaces the single-threaded no-op pthread_mutex stubs with a real, libc-free
threading leaf built directly on clone(2) and futex(2), so a static binary can
spawn worker threads — the last RTL piece needed for a libc-free static program
to do real multithreaded work.
runtime.thread.static.linux:
- pthread_create via raw clone(2): each thread gets its own mmap'd stack and a
fresh per-thread TLS block (CLONE_SETTLS) so threadvar access (exception
frames, the allocator) is per-thread. A small asm trampoline seeds the start
routine + arg onto the child stack, calls it, then exit(2) (thread-only).
- pthread_join via the CLONE_CHILD_CLEARTID futex word: the kernel clears it on
thread exit and futex-wakes; join futex-waits on it, then munmaps the stack.
- 3-state futex mutex (Drepper): the caller's pthread_mutex_t buffer's first
Integer is the futex word (0=unlocked, 1=locked, 2=contended); fast-path CAS,
slow-path FUTEX_WAIT/FUTEX_WAKE. sysconf is left to runtime.libc.linux.
runtime.syscall.linux: add the futex(2) syscall (SYS_futex, 6-arg, %rcx->%r10).
runtime.start.static.linux: capture the PT_TLS template at startup and expose
BuildThreadTLS so pthread_create can build each thread's TLS block the same way
_start builds the main thread's (variant II: TLS data then TCB self-pointer).
blaise.assembler.x86_64: add the xchg/cmpxchg encoders (xchgl/xchgq/cmpxchgl/
cmpxchgq, reg<->reg and reg<->mem) the futex mutex needs; strip brace comments
inside asm blocks in ParseLine (whole-line and trailing); and initialise
TParsedLine.HasLock to False so the lock prefix never carries between lines.
Verified: thrtest (8 worker threads x 10000 increments under the futex mutex)
prints counter=80000 PASS; QBE self-host FIXPOINT_OK.
The --static link path is currently blocked by a pre-existing self-host codegen
bug (spurious lock prefixes in large binaries built by a stage-2 compiler),
which is independent of this change and tracked separately.
b03f84c4c3