hakmem/core/ptr_trace.h

// ptr_trace.h - Pointer link read/write tracing (Debug-only, macro-replaceable)
//
// Purpose:
//  - Centrally instrument single-linked list next pointer reads/writes
//  - Zero overhead in release builds (macros devolve to raw ops)
//  - Compact TLS ring for triage; optional dump at exit via env
//
// Usage:
//  - Replace direct next ops with PTR_NEXT_WRITE / PTR_NEXT_READ
//  - Tag with a short literal (e.g., "tls_push", "tls_pop", "splice")
//  - Offsets should be header-aware (C0–C6: +1, C7: +0)
//
// Control:
//  - Compile-time: HAKMEM_PTR_TRACE (default: 1 for debug, 0 for release)
//  - Runtime dump: HAKMEM_PTR_TRACE_DUMP=1 (prints ring at exit)

#pragma once

#include <stdint.h>
#include <stddef.h>

#ifndef HAKMEM_PTR_TRACE
#  if !HAKMEM_BUILD_RELEASE
#    define HAKMEM_PTR_TRACE 1
#  else
#    define HAKMEM_PTR_TRACE 0
#  endif
#endif

#if HAKMEM_PTR_TRACE
#include <stdio.h>

typedef struct {
    const char* tag;   // literal tag
    int class_idx;     // tiny class (0..7)
    void* node;        // node address (base)
    void* val;         // written/read value
    size_t off;        // offset used for access
} ptr_trace_ev_t;

#ifndef PTR_TRACE_CAP
#  define PTR_TRACE_CAP 256
#endif

static __thread ptr_trace_ev_t g_ptr_trace_ring[PTR_TRACE_CAP];
static __thread uint32_t g_ptr_trace_idx = 0;
static __thread int g_ptr_trace_dump_registered = 0;

static inline void ptr_trace_record(const char* tag, int cls, void* node, void* val, size_t off) {
    uint32_t i = g_ptr_trace_idx++;
    g_ptr_trace_ring[i & (PTR_TRACE_CAP - 1)] = (ptr_trace_ev_t){ tag, cls, node, val, off };
}

static inline void ptr_trace_dump(void) {
    fprintf(stderr, "\n[PTR_TRACE_DUMP] last=%u (cap=%u)\n", g_ptr_trace_idx, (unsigned)PTR_TRACE_CAP);
    uint32_t n = (g_ptr_trace_idx < PTR_TRACE_CAP) ? g_ptr_trace_idx : PTR_TRACE_CAP;
    for (uint32_t k = 0; k < n; k++) {
        const ptr_trace_ev_t* e = &g_ptr_trace_ring[(g_ptr_trace_idx - n + k) & (PTR_TRACE_CAP - 1)];
        fprintf(stderr, "[%3u] tag=%s cls=%d node=%p val=%p off=%zu\n",
                k, e->tag ? e->tag : "?", e->class_idx, e->node, e->val, e->off);
    }
}

static inline void ptr_trace_try_register_dump(void) {
    if (g_ptr_trace_dump_registered) return;
    g_ptr_trace_dump_registered = 1;
    const char* env = getenv("HAKMEM_PTR_TRACE_DUMP");
    if (!(env && *env && *env != '0')) return;
    atexit(ptr_trace_dump);
}

// Immediate dump (Debug only) — static inline to avoid ODR/link conflicts under LTO
#if HAKMEM_PTR_TRACE
static inline void ptr_trace_dump_now(const char* reason) {
    fprintf(stderr, "\n[PTR_TRACE_NOW] reason=%s last=%u (cap=%u)\n",
            reason ? reason : "(null)", g_ptr_trace_idx, (unsigned)PTR_TRACE_CAP);
    uint32_t n = (g_ptr_trace_idx < PTR_TRACE_CAP) ? g_ptr_trace_idx : PTR_TRACE_CAP;
    for (uint32_t k = 0; k < n; k++) {
        const ptr_trace_ev_t* e = &g_ptr_trace_ring[(g_ptr_trace_idx - n + k) & (PTR_TRACE_CAP - 1)];
        fprintf(stderr, "[%3u] tag=%s cls=%d node=%p val=%p off=%zu\n",
                k, e->tag ? e->tag : "?", e->class_idx, e->node, e->val, e->off);
    }
}
#else
static inline void ptr_trace_dump_now(const char* reason) { (void)reason; }
#endif

#define PTR_NEXT_WRITE(tag, cls, node, off, value) do {                \
    void** __p = (void**)((uint8_t*)(node) + (off));                   \
    *__p = (value);                                                    \
    ptr_trace_record((tag), (cls), (node), (value), (off));            \
    ptr_trace_try_register_dump();                                     \
} while(0)

#define PTR_NEXT_READ(tag, cls, node, off, out_var) do {               \
    void** __p = (void**)((uint8_t*)(node) + (off));                   \
    (out_var) = *__p;                                                  \
    ptr_trace_record((tag), (cls), (node), (out_var), (off));          \
    ptr_trace_try_register_dump();                                     \
} while(0)

#else  // HAKMEM_PTR_TRACE == 0

#define PTR_NEXT_WRITE(tag, cls, node, off, value) \
    (*(void**)((uint8_t*)(node) + (off)) = (value))

#define PTR_NEXT_READ(tag, cls, node, off, out_var) \
    ((out_var) = *(void**)((uint8_t*)(node) + (off)))

// Always provide a stub for release builds so callers can link
static inline void ptr_trace_dump_now(const char* reason) { (void)reason; }

#endif // HAKMEM_PTR_TRACE