hakmem/core/box/superslab_expansion_box.c

// superslab_expansion_box.c - Box E: SuperSlab Expansion Implementation
// Purpose: Safe SuperSlab expansion with TLS state guarantee
// Box Theory: Complete encapsulation of expansion logic
//
// License: MIT
// Date: 2025-11-12

#include "superslab_expansion_box.h"
#include "../hakmem_tiny_superslab.h"  // expand_superslab_head(), g_superslab_heads
#include "../hakmem_tiny_superslab_constants.h"  // SUPERSLAB_SLAB0_DATA_OFFSET
#include <stdio.h>
#include <string.h>

// External SuperSlabHead array (defined in hakmem_tiny_superslab.c)
extern SuperSlabHead* g_superslab_heads[TINY_NUM_CLASSES_SS];

// External lock depth for safe fprintf in malloc context
extern __thread int g_hakmem_lock_depth;

// ============================================================================
// Box E: Core API Implementation
// ============================================================================

// Note: We don't implement expansion_capture_tls_state here because it requires
// access to g_tls_slabs, which is static in hakmem_tiny.c. The caller should
// capture state directly from their local g_tls_slabs reference.

ExpansionResult expansion_expand_with_tls_guarantee(
    SuperSlabHead* head,
    uint8_t class_idx)
{
    ExpansionResult result;
    memset(&result, 0, sizeof(result));
    result.success = false;
    result.error_code = -2;  // Invalid params

    // Validate parameters
    if (!head || class_idx >= TINY_NUM_CLASSES_SS) {
        return result;
    }

    // CRITICAL: Call existing expand_superslab_head() with mutex protection
    // This function already handles:
    // 1. Mutex lock/unlock (head->expansion_lock)
    // 2. Double-check pattern (re-verify after lock)
    // 3. Chunk allocation and linking
    // 4. current_chunk update
    int expand_result = expand_superslab_head(head);

    if (expand_result < 0) {
        // Expansion failed (OOM)
        result.success = false;
        result.error_code = -1;  // OOM
        return result;
    }

    // Expansion succeeded
    // CRITICAL FIX: Bind slab 0 immediately to prevent NULL meta SEGV
    // The new chunk always has slab 0 available after expansion
    SuperSlab* new_ss = head->current_chunk;

    // Initialize slab 0 metadata (set capacity, mark as active in bitmap)
    extern void superslab_init_slab(SuperSlab* ss, int slab_idx, size_t block_size, uint32_t owner_tid);
    extern const size_t g_tiny_class_sizes[];

    uint32_t my_tid = (uint32_t)(uintptr_t)pthread_self();
    size_t block_size = g_tiny_class_sizes[class_idx];
    superslab_init_slab(new_ss, 0, block_size, my_tid);

    // CRITICAL FIX: Explicitly set class_idx to avoid C0/C7 confusion.
    // New SuperSlabs start with meta->class_idx=0 (mmap zero-init).
    new_ss->slabs[0].class_idx = (uint8_t)class_idx;

    // Now bind slab 0 to TLS state
    result.new_state.ss = new_ss;
    result.new_state.class_idx = class_idx;
    result.new_state.slab_idx = 0;  // Always bind slab 0 after expansion
    result.new_state.meta = &new_ss->slabs[0];  // Point to slab 0 metadata

    // Calculate slab_base using tiny_slab_base_for_geometry logic
    // Slab 0 has offset SUPERSLAB_SLAB0_DATA_OFFSET (2048 bytes)
    // Formula: base = ss + (slab_idx * SLAB_SIZE) + (slab_idx == 0 ? SLAB0_OFFSET : 0)
    result.new_state.slab_base = (uint8_t*)new_ss + SUPERSLAB_SLAB0_DATA_OFFSET;

    // Debug: log backend used for expansion (first few only)
    static _Atomic uint32_t g_ss_backend_log = 0;
    uint32_t n = atomic_fetch_add_explicit(&g_ss_backend_log, 1, memory_order_relaxed);
    if (n < 4) {
        fprintf(stderr, "[SS_BACKEND] expand legacy cls=%d ss=%p slab_idx=0 base=%p\n",
                class_idx, (void*)new_ss, result.new_state.slab_base);
    }

    result.success = true;
    result.error_code = 0;

    return result;
}

void expansion_apply_tls_state(
    uint8_t class_idx,
    const ExpansionTLSState* new_state,
    TinyTLSSlab* tls_array)
{
    if (!new_state || !tls_array || class_idx >= TINY_NUM_CLASSES_SS) {
        return;
    }

    TinyTLSSlab* tls = &tls_array[class_idx];

    // CRITICAL FIX: Apply complete TLS state from expansion
    // This ensures meta and slab_base are NEVER NULL after expansion
    tls->ss = new_state->ss;
    tls->meta = new_state->meta;           // ✅ Now points to slab 0!
    tls->slab_base = new_state->slab_base; // ✅ Now points to slab 0 base!
    tls->slab_idx = new_state->slab_idx;   // ✅ Now 0 (slab 0)
}

// ============================================================================
// Box E: Debug & Validation Implementation
// ============================================================================

#if !defined(HAKMEM_BUILD_RELEASE) || defined(HAKMEM_EXPANSION_BOX_DEBUG)

bool expansion_validate_tls_state(
    const ExpansionTLSState* state,
    const char* context)
{
    if (!state) {
        return false;
    }

    // Allow NULL ss (initial state before any allocation)
    if (!state->ss) {
        return true;
    }

    // Validate SuperSlab magic
    if (state->ss->magic != SUPERSLAB_MAGIC) {
        g_hakmem_lock_depth++;
        fprintf(stderr, "[EXPANSION_VAL] %s: Invalid SuperSlab magic: 0x%016llx (expected 0x%016llx)\n",
                context, (unsigned long long)state->ss->magic, (unsigned long long)SUPERSLAB_MAGIC);
        g_hakmem_lock_depth--;
        return false;
    }

    // Validate class consistency
    if (state->ss->size_class != state->class_idx) {
        g_hakmem_lock_depth++;
        fprintf(stderr, "[EXPANSION_VAL] %s: Class mismatch: ss->size_class=%u, state->class_idx=%u\n",
                context, state->ss->size_class, state->class_idx);
        g_hakmem_lock_depth--;
        return false;
    }

    // Validate slab index bounds
    int capacity = (state->ss->lg_size == 21) ? 32 : 16;  // 2MB=32 slabs, 1MB=16 slabs
    if (state->slab_idx >= capacity) {
        g_hakmem_lock_depth++;
        fprintf(stderr, "[EXPANSION_VAL] %s: slab_idx out of bounds: %u >= %d\n",
                context, state->slab_idx, capacity);
        g_hakmem_lock_depth--;
        return false;
    }

    // Validate meta pointer alignment (should point into ss->slabs array)
    if (state->meta) {
        TinySlabMeta* expected_meta = &state->ss->slabs[state->slab_idx];
        if (state->meta != expected_meta) {
            g_hakmem_lock_depth++;
            fprintf(stderr, "[EXPANSION_VAL] %s: meta pointer mismatch: %p (expected %p)\n",
                    context, (void*)state->meta, (void*)expected_meta);
            g_hakmem_lock_depth--;
            return false;
        }
    }

    // Validate slab_base alignment (should be within SuperSlab memory range)
    if (state->slab_base) {
        uintptr_t ss_start = (uintptr_t)state->ss;
        size_t ss_size = (size_t)1 << state->ss->lg_size;
        uintptr_t ss_end = ss_start + ss_size;
        uintptr_t base_addr = (uintptr_t)state->slab_base;

        if (base_addr < ss_start || base_addr >= ss_end) {
            g_hakmem_lock_depth++;
            fprintf(stderr, "[EXPANSION_VAL] %s: slab_base out of range: %p (ss: %p - %p)\n",
                    context, (void*)state->slab_base, (void*)ss_start, (void*)ss_end);
            g_hakmem_lock_depth--;
            return false;
        }
    }

    return true;
}

bool expansion_verify_expansion(
    SuperSlabHead* head,
    const ExpansionTLSState* old_state,
    const ExpansionTLSState* new_state)
{
    if (!head || !old_state || !new_state) {
        return false;
    }

    // Verify new chunk is set
    if (!new_state->ss) {
        g_hakmem_lock_depth++;
        fprintf(stderr, "[EXPANSION_VERIFY] New state has NULL SuperSlab\n");
        g_hakmem_lock_depth--;
        return false;
    }

    // Verify current_chunk was updated
    if (head->current_chunk != new_state->ss) {
        g_hakmem_lock_depth++;
        fprintf(stderr, "[EXPANSION_VERIFY] current_chunk mismatch: head=%p, new_state=%p\n",
                (void*)head->current_chunk, (void*)new_state->ss);
        g_hakmem_lock_depth--;
        return false;
    }

    // Verify new chunk has available capacity (bitmap should not be full)
    int capacity = (new_state->ss->lg_size == 21) ? 32 : 16;
    uint32_t full_mask = (capacity >= 32) ? 0xFFFFFFFF : ((1U << capacity) - 1);

    if (new_state->ss->slab_bitmap == full_mask) {
        g_hakmem_lock_depth++;
        fprintf(stderr, "[EXPANSION_VERIFY] New chunk has no free slabs: bitmap=0x%08x\n",
                new_state->ss->slab_bitmap);
        g_hakmem_lock_depth--;
        return false;
    }

    // Verify total_chunks was incremented (if we can check old value)
    // Note: We can't reliably check this without capturing old value
    // But we can verify it's at least 1
    size_t total = atomic_load_explicit(&head->total_chunks, memory_order_relaxed);
    if (total == 0) {
        g_hakmem_lock_depth++;
        fprintf(stderr, "[EXPANSION_VERIFY] total_chunks is 0 after expansion\n");
        g_hakmem_lock_depth--;
        return false;
    }

    return true;
}

void expansion_log_event(
    const char* event,
    uint8_t class_idx,
    const ExpansionTLSState* state)
{
    if (!event || !state) {
        return;
    }

    g_hakmem_lock_depth++;

    if (state->ss) {
        fprintf(stderr, "[EXPANSION] class=%u %s: ss=%p, bitmap=0x%08x, active=%u, slab_idx=%u\n",
                class_idx, event,
                (void*)state->ss,
                state->ss->slab_bitmap,
                state->ss->active_slabs,
                state->slab_idx);
    } else {
        fprintf(stderr, "[EXPANSION] class=%u %s: ss=NULL (initial state)\n",
                class_idx, event);
    }

    g_hakmem_lock_depth--;
}

#endif // !HAKMEM_BUILD_RELEASE || HAKMEM_EXPANSION_BOX_DEBUG