1# Memory Leak Check<a name="EN-US_TOPIC_0000001079076672"></a> 2 3- [Basic Concepts](#section1026719436293) 4- [Function Configuration](#section13991354162914) 5- [Development Guidelines](#section95828159308) 6 - [How to Develop](#section369844416304) 7 - [Development Example](#section460801313313) 8 - [Sample Code](#section96539275311) 9 - [Verification](#section20527343183119) 10 11 12## Basic Concepts<a name="section1026719436293"></a> 13 14As an optional function of the kernel, memory leak check is used to locate dynamic memory leak problems. After this function is enabled, the dynamic memory automatically records the link registers \(LRs\) used when memory is allocated. If a memory leak occurs, the recorded information helps locate the memory allocated for further analysis. 15 16## Function Configuration<a name="section13991354162914"></a> 17 181. **LOSCFG\_MEM\_LEAKCHECK**: specifies the setting of the memory leak check. This function is disabled by default. To enable the function, set this macro to **1** in **target\_config.h**. 192. **LOSCFG\_MEM\_RECORD\_LR\_CNT**: number of LRs recorded. The default value is **3**. Each LR consumes the memory of **sizeof\(void \*\)** bytes. 203. **LOSCFG\_MEM\_OMIT\_LR\_CNT**: number of ignored LRs. The default value is **4**, which indicates that LRs are recorded from the time when **LOS\_MemAlloc** is called. You can change the value based on actual requirements. This macro is configured because: 21 - **LOS\_MemAlloc** is also called internally. 22 - **LOS\_MemAlloc** may be encapsulated externally. 23 - The number of LRs configured by **LOSCFG\_MEM\_RECORD\_LR\_CNT** is limited. 24 25 26Correctly setting this macro can ignore invalid LRs and reduce memory consumption. 27 28## Development Guidelines<a name="section95828159308"></a> 29 30### How to Develop<a name="section369844416304"></a> 31 32Memory leak check provides a method to check for memory leak in key code logic. If this function is enabled, LR information is recorded each time when memory is allocated. When **LOS\_MemUsedNodeShow** is called before and after the code snippet is checked, information about all nodes that have been used in the specified memory pool is printed. You can compare the node information. The newly added node information indicates the node where the memory leak may occur. You can locate the code based on the LR and further check whether a memory leak occurs. 33 34The node information output by calling **LOS\_MemUsedNodeShow** is in the following format: Each line contains information about a node. The first column indicates the node address, based on which you can obtain complete node information using a tool such as a GNU Debugger \(GDB\). The second column indicates the node size, which is equal to the node header size plus the data field size. Columns 3 to 5 list the LR addresses. You can determine the specific memory location of the node based on the LR addresses and the assembly file. 35 36``` 37node size LR[0] LR[1] LR[2] 380x10017320: 0x528 0x9b004eba 0x9b004f60 0x9b005002 390x10017848: 0xe0 0x9b02c24e 0x9b02c246 0x9b008ef0 400x10017928: 0x50 0x9b008ed0 0x9b068902 0x9b0687c4 410x10017978: 0x24 0x9b008ed0 0x9b068924 0x9b0687c4 420x1001799c: 0x30 0x9b02c24e 0x9b02c246 0x9b008ef0 430x100179cc: 0x5c 0x9b02c24e 0x9b02c246 0x9b008ef0 44``` 45 46> **CAUTION:** 47>Enabling memory leak check affects memory application performance. LR addresses will be recorded for each memory node, increasing memory overhead. 48 49### Development Example<a name="section460801313313"></a> 50 51This example implements the following: 52 531. Calls **LOS\_MemUsedNodeShow** to print information about all nodes. 542. Simulates a memory leak by requesting memory without releasing it. 553. Calls **LOS\_MemUsedNodeShow** to print information about all nodes. 564. Compare the logs to obtain information about the node where a memory leak occurred. 575. Locate the code based on the LR address. 58 59### Sample Code<a name="section96539275311"></a> 60 61The sample code is as follows: 62 63``` 64#include <stdio.h> 65#include <string.h> 66#include "los_memory.h" 67#include "los_config.h" 68 69void MemLeakTest(void) 70{ 71 LOS_MemUsedNodeShow(LOSCFG_SYS_HEAP_ADDR); 72 void *ptr1 = LOS_MemAlloc(LOSCFG_SYS_HEAP_ADDR, 8); 73 void *ptr2 = LOS_MemAlloc(LOSCFG_SYS_HEAP_ADDR, 8); 74 LOS_MemUsedNodeShow(LOSCFG_SYS_HEAP_ADDR); 75} 76``` 77 78### Verification<a name="section20527343183119"></a> 79 80The log is as follows: 81 82``` 83node size LR[0] LR[1] LR[2] 840x20001b04: 0x24 0x08001a10 0x080035ce 0x080028fc 850x20002058: 0x40 0x08002fe8 0x08003626 0x080028fc 860x200022ac: 0x40 0x08000e0c 0x08000e56 0x0800359e 870x20002594: 0x120 0x08000e0c 0x08000e56 0x08000c8a 880x20002aac: 0x56 0x08000e0c 0x08000e56 0x08004220 89 90node size LR[0] LR[1] LR[2] 910x20001b04: 0x24 0x08001a10 0x080035ce 0x080028fc 920x20002058: 0x40 0x08002fe8 0x08003626 0x080028fc 930x200022ac: 0x40 0x08000e0c 0x08000e56 0x0800359e 940x20002594: 0x120 0x08000e0c 0x08000e56 0x08000c8a 950x20002aac: 0x56 0x08000e0c 0x08000e56 0x08004220 960x20003ac4: 0x1d 0x08001458 0x080014e0 0x080041e6 970x20003ae0: 0x1d 0x080041ee 0x08000cc2 0x00000000 98``` 99 100The difference between the two logs is as follows. The following memory nodes are suspected to have blocks with a memory leak. 101 102``` 1030x20003ac4: 0x1d 0x08001458 0x080014e0 0x080041e6 1040x20003ae0: 0x1d 0x080041ee 0x08000cc2 0x00000000 105``` 106 107The following is part of the assembly file: 108 109``` 110 MemLeakTest: 111 0x80041d4: 0xb510 PUSH {R4, LR} 112 0x80041d6: 0x4ca8 LDR.N R4, [PC, #0x2a0] ; g_memStart 113 0x80041d8: 0x0020 MOVS R0, R4 114 0x80041da: 0xf7fd 0xf93e BL LOS_MemUsedNodeShow ; 0x800145a 115 0x80041de: 0x2108 MOVS R1, #8 116 0x80041e0: 0x0020 MOVS R0, R4 117 0x80041e2: 0xf7fd 0xfbd9 BL LOS_MemAlloc ; 0x8001998 118 0x80041e6: 0x2108 MOVS R1, #8 119 0x80041e8: 0x0020 MOVS R0, R4 120 0x80041ea: 0xf7fd 0xfbd5 BL LOS_MemAlloc ; 0x8001998 121 0x80041ee: 0x0020 MOVS R0, R4 122 0x80041f0: 0xf7fd 0xf933 BL LOS_MemUsedNodeShow ; 0x800145a 123 0x80041f4: 0xbd10 POP {R4, PC} 124 0x80041f6: 0x0000 MOVS R0, R0 125``` 126 127The memory node addressed by **0x080041ee** is not released after being requested in **MemLeakTest**. 128 129
