Remove SystemAllocateMemory's hidden 4-byte tag-header scheme.

The HEAP/MMAP tag word written just before every allocated pointer (to
let SystemFreeMemory dispatch to free() vs munmap()) unconditionally
shifted every allocation 4 bytes off whatever alignment malloc actually
provided. The mmap path was permanently dead code (if (0), condition
commented out) -- malloc is the only allocator ever used -- so the tag
was pure overhead with no benefit, and it was silently defeating
g_pHashTable's deliberate 4-entries-per-cache-line (16 bytes x 4 = 64
bytes) layout: verified via lldb that the table was consistently
offset by exactly 4 bytes from a 64-byte boundary before this change,
and is now consistently 64-byte aligned across multiple runs.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01C9r36BydPnfpyYLFhkTo6d

1 files changed, 3 insertions, 112 deletions

diff --git a/src/unix.c b/src/unix.c
index 564e0af..2c90f7f 100644
--- a/src/unix.c
+++ b/src/unix.c
@@ -31,10 +31,6 @@ Revision History:
 #include <signal.h>
 #include <errno.h>
 
-#define SYS_MAX_HEAP_ALLOC_SIZE_BYTES 0xfff
-#define HEAP 0x48656170
-#define MMAP 0x4d6d6170
-
 pthread_mutex_t g_SystemLock;
 #define LOCK_SYSTEM     pthread_mutex_lock(&g_SystemLock)
 #define UNLOCK_SYSTEM   pthread_mutex_unlock(&g_SystemLock)
@@ -518,68 +514,6 @@ Return value:
 }
 
 
-static void *
-_SystemCallMmap(ULONG dwSizeBytes)
-/**
-
-Routine description:
-
-    Wrapper around mmap.
-
-Parameters:
-
-    ULONG dwSizeBytes
-
-Return value:
-
-    static void
-
-**/
-{
-    void *pMem = mmap(0,
-                      (size_t)dwSizeBytes,
-                      PROT_READ | PROT_WRITE,
-                      MAP_ANON,
-                      -1,
-                      0);
-    if (MAP_FAILED == pMem)
-    {
-        UtilPanic(UNEXPECTED_SYSTEM_CALL_FAILURE,
-                  NULL, "mmap", (void *)(size_t)errno, (void *)(size_t)dwSizeBytes,
-                  __FILE__, __LINE__);
-    }
-    (void)madvise(pMem, dwSizeBytes, MADV_RANDOM | MADV_WILLNEED);
-    return(pMem);
-}
-
-
-static void 
-_SystemCallMunmap(void *pMem)
-/**
-
-Routine description:
-
-    Wrapper around munmap
-
-Parameters:
-
-    void *pMem
-
-Return value:
-
-    static void
-
-**/
-{
-    if (0 != munmap(pMem, (size_t)-1))
-    {
-        UtilPanic(UNEXPECTED_SYSTEM_CALL_FAILURE,
-                  NULL, "munmap", (void *)(size_t)errno, pMem,
-                  __FILE__, __LINE__);
-    }
-}
-
-
 static void *_SystemCallMalloc(ULONG dwSizeBytes)
 /**
 
@@ -671,32 +605,7 @@ Return value:
 
 **/
 {
-    DWORD *p;
-
-    if (0) // (dwSizeBytes > SYS_MAX_HEAP_ALLOC_SIZE_BYTES)
-    {
-        p = _SystemCallMmap(dwSizeBytes + sizeof(DWORD));
-        if (NULL == p)
-        {
-            UtilPanic(UNEXPECTED_SYSTEM_CALL_FAILURE,
-                      NULL, "mmap", (void *)(size_t)errno, NULL,
-                      __FILE__, __LINE__);
-        }
-        *p = MMAP;
-        p += 1;
-    }
-    else
-    {
-        p = _SystemCallMalloc(dwSizeBytes + sizeof(DWORD));
-        if (NULL == p)
-        {
-            UtilPanic(UNEXPECTED_SYSTEM_CALL_FAILURE,
-                      NULL, "malloc", (void *)(size_t)errno, NULL,
-                      __FILE__, __LINE__);
-        }
-        *p = HEAP;
-        p += 1;
-    }
+    void *p = _SystemCallMalloc(dwSizeBytes);
 #ifdef DEBUG
     MarkAllocHashEntry(p, dwSizeBytes);
 #endif
@@ -704,7 +613,7 @@ Return value:
     return(p);
 }
 
-void 
+void
 SystemFreeMemory(void *pMemory)
 /**
 
@@ -722,28 +631,10 @@ Return value:
 
 **/
 {
-    DWORD *p = pMemory;
-    
-    p -= 1;
 #ifdef DEBUG
     ReleaseAllocHashEntry(pMemory);
 #endif
-    if (*p == HEAP)
-    {
-        _SystemCallFree(p);
-    }
-    else if (*p == MMAP)
-    {
-        _SystemCallMunmap(p);
-    }
-#ifdef DEBUG
-    else
-    {
-        UtilPanic(SHOULD_NOT_GET_HERE,
-                  NULL, NULL, NULL, NULL,
-                  __FILE__, __LINE__);
-    }
-#endif
+    _SystemCallFree(pMemory);
 }