feat(thread): futex + TLS + pthread_self substrate

src/start/tcb.h

@@ -74,6 +74,9 @@
 
 #include "../internal/errno.h" /* VLIBC_TCB_ERRNO_OFF */
 
+#include <stddef.h>
+#include <stdint.h>
+
 #define VLIBC_TCB_SELF_OFF 0
 
 /* VLIBC_TCB_ERRNO_OFF (8) is consumed from src/internal/errno.h. */
@@ -84,4 +87,31 @@
 
 #define VLIBC_TCB_SIZE 24
 
+/*
+ * New-thread TLS geometry (todo 44). All four are set by init_main_tls()
+ * in src/start/tls.c and read by src/thread/tls.c (__vlibc_tls_setup):
+ *
+ *   __vlibc_static_tls_size    PT_TLS p_memsz of the main executable — the
+ *                              one DEFAULT-VISIBILITY EXPORTED symbol of
+ *                              the group: #62 grows it on dlopen, #45 reads
+ *                              it when sizing new-thread TLS blocks.
+ *   __vlibc_static_tls_filesz  PT_TLS p_filesz (.tdata part).
+ *   __vlibc_static_tls_align   PT_TLS p_align (16 when there is no PT_TLS).
+ *   __vlibc_static_tls_template the PRIMAL TLS image address: the mapped
+ *                              .tdata at p_vaddr, never the main thread's
+ *                              LIVE TLS block (which mutates). In the
+ *                              file-fallback path it is the main block
+ *                              itself — the only copy that exists then.
+ *
+ * The three hidden ones keep their attribute on the definitions (as with
+ * environ's hidden alias in src/start/environ.c); __vlibc_static_tls_size
+ * deliberately carries none so it stays an exported ABI object.
+ */
+// NOLINTBEGIN(bugprone-reserved-identifier)
+extern size_t __vlibc_static_tls_size;
+extern uintptr_t __vlibc_static_tls_template;
+extern size_t __vlibc_static_tls_filesz;
+extern size_t __vlibc_static_tls_align;
+// NOLINTEND(bugprone-reserved-identifier)
+
 #endif /* VLIBC_INTERNAL_START_TCB_H */