#ifndef VLIBC_INTERNAL_START_TCB_H
#define VLIBC_INTERNAL_START_TCB_H

/*
 * vlibc — AUTHORITATIVE x86_64 TCB / thread-pointer layout (todo 3).
 *
 * This header defines the thread control block (TCB) layout ONCE, for the
 * whole library. Later layers reference these constants and NEVER redefine
 * them:
 *
 *   #44  threading substrate: clones this layout for every new thread and
 *        initializes the fenv slot per thread.
 *   #45  sizes new-thread TLS from the static TLS block arithmetic below.
 *   #62  ld.so: performs the dynamic-case equivalent of this bootstrap (the
 *        FS-already-set guard in tls.c skips this code in that case).
 *   #42  fenv: reads/writes the reserved fenv slot through the fixed
 *        offsets below; the slot is per-thread lazy storage for the x87
 *        control word and MXCSR.
 *
 * ABI model — ELF TLS variant II on x86_64:
 *
 * The thread pointer (TP) is delivered by the %fs segment and points
 * DIRECTLY at the TCB (this is what "variant II" means; variant I, used by
 * e.g. 32-bit x86, points at the end of the TLS data instead). Static TLS
 * data live at NEGATIVE offsets from TP (%fs:N with N < 0, the LE model);
 * the TCB fields live at positive offsets. Slot 0 is required to hold the
 * TCB's own address because __builtin_thread_pointer() reads %fs:0 — that
 * is the entire mechanism by which C code recovers TP from a register.
 *
 * TCB field map (offsets are byte offsets from TP, i.e. from %fs:0):
 *
 *   TP +  0  VLIBC_TCB_SELF_OFF    TCB self pointer (TP itself).
 *   TP +  8  VLIBC_TCB_ERRNO_OFF   per-thread errno slot: 8 bytes, errno
 *                                   occupies the low 4. This offset is OWNED
 *                                   by src/internal/errno.h (task 1 fixed it
 *                                   as an ABI constant) and is consumed
 *                                   here, never re-derived.
 *   TP + 16  VLIBC_TCB_FENV_OFF    per-thread fenv reservation, 8 bytes:
 *             +16 VLIBC_TCB_FENV_X87CW_OFF  uint16 x87 control word,
 *                                           reset default 0x037F (double
 *                                           precision, round-to-nearest)
 *             +18 (pad, reserved)
 *             +20 VLIBC_TCB_FENV_MXCSR_OFF  uint32 MXCSR, reset default
 *                                           0x1F80 (all exceptions masked)
 *   TP + 24  end of the fixed layout; VLIBC_TCB_SIZE = 24.
 *
 * The layout grows FORWARD from TP if later layers need more TCB fields;
 * the fixed slots above are never renumbered. A DTV pointer is deliberately
 * NOT reserved: the static TLS model needs no DTV (every access is
 * %fs-relative with a link-time offset; there is no __tls_get_addr). Should
 * #62's dynamic TLS ever require a DTV, add it at TP + VLIBC_TCB_SIZE —
 * glibc's variant-II convention keeps the DTV at a negative offset relative
 * to a separately allocated block; vlibc deliberately keeps the simpler
 * grow-upward model documented here.
 *
 * Static TLS placement contract (tls.c implements this; the linker bakes
 * its TPOFF arithmetic against the same formula, verified empirically with
 * GNU ld):
 *
 *   - tp = base + round_up(p_memsz, p_align), with base page-aligned.
 *   - the PT_TLS image is copied to [base, base + p_filesz), the BSS tail
 *     [base + p_filesz, base + p_memsz) is zeroed, and the TCB occupies
 *     [tp, tp + VLIBC_TCB_SIZE).
 *   - TP alignment equals p_align EXACTLY (never bumped to 16): the linker
 *     computes tpoff = var_offset - round_up(p_memsz, p_align), so any
 *     other rounding breaks every %fs offset when p_memsz is not a
 *     multiple of the runtime's alignment. When the program has no PT_TLS
 *     at all, p_align is taken as 16 and the block is TCB-only.
 *
 *     TCB fields only need 8-byte alignment, and the linker guarantees
 *     p_align >= the alignment of every TLS object, so the exact-p_align
 *     rule is always sufficient.
 */

#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. */

#define VLIBC_TCB_FENV_OFF 16
#define VLIBC_TCB_FENV_X87CW_OFF (VLIBC_TCB_FENV_OFF + 0)
#define VLIBC_TCB_FENV_MXCSR_OFF (VLIBC_TCB_FENV_OFF + 4)

#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 */