c2716f5c01
- Feature: Added HAKMEM_TINY_HEADERLESS toggle (A/B testing) - Feature: Implemented Headerless layout logic (Offset=0) - Refactor: Centralized layout definitions in tiny_layout_box.h - Refactor: Abstracted pointer arithmetic in free path via ptr_conversion_box.h - Verification: sh8bench passes in Headerless mode (No TLS_SLL_HDR_RESET) - Known Issue: Regression in Phase 1 mode due to blind pointer conversion logic
79 lines
2.6 KiB
C
79 lines
2.6 KiB
C
/**
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* @file tiny_layout_box.h
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* @brief Box: Tiny Allocator Layout Definitions
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*
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* MISSION: Single source of truth for class size and header layout
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*
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* Current Design (Phase E1-CORRECT):
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* - All classes (0-7) have 1-byte header
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* - User pointer = base + 1 for classes 0-6, base + 0 for class 7
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* (Note: Class 7 is headerless in practice but marked for consistency)
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* - No external code should hardcode offsets
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*/
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#ifndef TINY_LAYOUT_BOX_H
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#define TINY_LAYOUT_BOX_H
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#include <stddef.h>
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#include "../hakmem_tiny_config.h" // For g_tiny_class_sizes and TINY_NUM_CLASSES
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// A/B Toggle: Headerless mode
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// ENV: HAKMEM_TINY_HEADERLESS=1 to enable
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// Default: 0 (Phase 1 compatible)
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#ifndef HAKMEM_TINY_HEADERLESS
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#define HAKMEM_TINY_HEADERLESS 0
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#endif
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// Define all class-specific layout parameters
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// Current: Defined in g_tiny_class_sizes[8] in hakmem_tiny.c
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// This file makes them accessible via a unified Box API
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// Header size
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static inline size_t tiny_header_size(int class_idx) {
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#if HAKMEM_TINY_HEADERLESS
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(void)class_idx;
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return 0;
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#else
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// Phase 1: 1 byte header if enabled
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// C0 (8B): offset 0 (8B stride too small for header + 8B pointer - would overflow)
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// C7 (2048B): offset 0 (overwrites header in freelist - largest class can tolerate)
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// C1-C6: offset 1 (header preserved - user data is not disturbed)
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return (0x7Eu >> class_idx) & 1u;
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#endif
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}
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// Legacy macro for backward compatibility (Phase 1)
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#define TINY_HEADER_SIZE 1
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// Validation macros
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static inline int tiny_class_is_valid(int class_idx) {
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return class_idx >= 0 && class_idx < TINY_NUM_CLASSES;
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}
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static inline size_t tiny_class_stride(int class_idx) {
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// Use the extern global definition from hakmem_tiny_config.h
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// g_tiny_class_sizes is defined in core/hakmem_tiny_config_box.inc
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return tiny_class_is_valid(class_idx) ? g_tiny_class_sizes[class_idx] : 0;
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}
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// Calculate user pointer offset from base pointer
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// This logic centralizes the "User = Base + 1" vs "User = Base + 0" decision
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static inline size_t tiny_user_offset(int class_idx) {
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#if HAKMEM_TINY_HEADERLESS
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(void)class_idx;
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return 0; // Headerless: user = base
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#elif HAKMEM_TINY_HEADER_CLASSIDX
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// C0 (8B): offset 0 (8B stride too small for header + 8B pointer - would overflow)
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// C7 (2048B): offset 0 (overwrites header in freelist - largest class can tolerate)
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// C1-C6: offset 1 (header preserved - user data is not disturbed)
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// Optimized: Use bitmask lookup instead of branching
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// Bit pattern: C0=0, C1-C6=1, C7=0 → 0b01111110 = 0x7E
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return (0x7Eu >> class_idx) & 1u;
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#else
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(void)class_idx;
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return 0u;
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#endif
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}
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#endif // TINY_LAYOUT_BOX_H
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