2017-1-15-libubox analysis

2017-1-15-libubox analysis

libubox

• utils.h

utils.h

提供了一些简单的实用工具函数。比如大小端转换，位图操作，编译器属性的封装，连续内存申请函数calloc_a，静态计算数组大小的宏，断言/调试的实用工具,苹果兼容的时钟获取时间的封装，base64编解码。

1. /* 
   

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2. *  
   

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3. * calloc_a(size_t len, [void **addr, size_t len,...], NULL) 
   

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4. * 申请一个足够大内存块来保存多个对齐的对象。 
   

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5. * 返回一个指针，指针指向全部对象（以第一个块开始）注意：释放这个指针将释放所有全部对象的内存 
   

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6. * 所有其它指针被保存在额外的addr参数指向的位置。 
   

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7. * 最后一个参数必须是NULL指针 
   

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8. */ 
   

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9. ---

10. #define calloc_a(len, ...) __calloc_a(len, ##__VA_ARGS__, NULL) 
    

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11. void *__calloc_a(size_t len, ...); 
    

    ---

12. ---

calloc_a示例:

1. #include <string.h> 
   

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2. #include <libubox/utils.h> 
   

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3. ---

4. struct sleeper { 
   

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5. int aa; 
   

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6. int bb; 
   

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7. }; 
   

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8. ---

9. #define NAME_LEN 32 
   

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10. int main(int argc, char **argv) 
    

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11. { 
    

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12. struct sleeper *s; 
    

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13. char *name; 
    

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14. int *a1; 
    

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15. s = (struct sleeper *)calloc_a(sizeof(*s), &name, NAME_LEN, &a1, sizeof(*a1)); 
    

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16. s->aa = 0x10101010; 
    

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17. s->bb = 0x20202020; 
    

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18. strncpy(name, "SSSSSSSSSSSSSSSSSSSSSSSS", NAME_LEN-1); 
    

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19. name[NAME_LEN-1] = '\0'; 
    

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20. *a1 = 0xaaaaaaaa; 
    

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21. free(s); 
    

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22. return 0; 
    

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23. } 
    

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24. ---

25. (gdb) x/20x s 
    

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26. 0x602010: 0x10101010 0x20202020 0x53535353 0x53535353 
    

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27. 0x602020: 0x53535353 0x53535353 0x53535353 0x53535353 
    

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28. 0x602030: 0x00000000 0x00000000 0xaaaaaaaa 0x00000000 
    

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1. /* 
   

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2. * 计算数组大小 
   

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3. */ 
   

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4. #ifndef ARRAY_SIZE 
   

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5. #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0])) 
   

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6. #endif 
   

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1. /* 
   

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2. * BUILD_BUG_ON基于一个GCC不支持负数数组，在编译时报错 
   

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3. * 但是4.4后GCC支持变长数组，不会引起编译器报错。 
   

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4. * 加入GCC优化选项后，编译时不会错，但是链接时会有找不到符号__BUILD_BUG_ON_CONDITION_FAILED的错误 
   

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5. */ 
   

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6. #define __BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)])) 
   

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7. ---

8. #ifdef __OPTIMIZE__ 
   

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9. extern int __BUILD_BUG_ON_CONDITION_FAILED; 
   

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10. #define BUILD_BUG_ON(condition) \ 
    

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11. do { \ 
    

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12. __BUILD_BUG_ON(condition); \ 
    

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13. if (condition) \ 
    

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14. __BUILD_BUG_ON_CONDITION_FAILED = 1; \ 
    

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15. } while(0) 
    

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16. #else 
    

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17. #define BUILD_BUG_ON __BUILD_BUG_ON 
    

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18. #endif 
    

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FIXUP for BUILD_BUG_ON：

1. /* Force a compilation error if condition is true */ 
   

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2. -#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)])) 
   

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3. +#define BUILD_BUG_ON(condition) ((void)BUILD_BUG_ON_ZERO(condition)) 
   

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4. + 
   

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5. +/* Force a compilation error if condition is constant and true */ 
   

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6. +#define MAYBE_BUILD_BUG_ON(cond) ((void)sizeof(char[1 - 2 * !!(cond)])) 
   

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7. ---

8. /* Force a compilation error if condition is true, but also produce a 
   

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9. result (of value 0 and type size_t), so the expression can be used 
   

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10. e.g. in a structure initializer (or where-ever else comma expressions 
    

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11. aren't permitted). */ 
    

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12. -#define BUILD_BUG_ON_ZERO(e) (sizeof(char[1 - 2 * !!(e)]) - 1) 
    

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13. +#define BUILD_BUG_ON_ZERO(e) (sizeof(struct { int:-!!(e); })) 
    

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14. +#define BUILD_BUG_ON_NULL(e) ((void *)sizeof(struct { int:-!!(e); })) 
    

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1. /* 
   

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2. */ 
   

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3. #ifdef __APPLE__ 
   

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4. ---

5. #define CLOCK_REALTIME 0 
   

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6. #define CLOCK_MONOTONIC 1 
   

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7. ---

8. void clock_gettime(int type, struct timespec *tv); 
   

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9. ---

10. #endif 
    

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1. #ifdef __GNUC__ 
   

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2. #define _GNUC_MIN_VER(maj, min) (((__GNUC__ << 8) + __GNUC_MINOR__) >= (((maj) << 8) + (min))) 
   

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3. #else 
   

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4. #define _GNUC_MIN_VER(maj, min) 0 
   

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5. #endif 
   

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6. ---

7. #if defined(__linux__) || defined(__CYGWIN__) 
   

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8. #include <byteswap.h> 
   

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9. #include <endian.h> 
   

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10. ---

11. #elif defined(__APPLE__) 
    

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12. #include <machine/endian.h> 
    

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13. #include <machine/byte_order.h> 
    

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14. #define bswap_32(x) OSSwapInt32(x) 
    

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15. #define bswap_64(x) OSSwapInt64(x) 
    

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16. #elif defined(__FreeBSD__) 
    

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17. #include <sys/endian.h> 
    

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18. #define bswap_32(x) bswap32(x) 
    

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19. #define bswap_64(x) bswap64(x) 
    

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20. #else 
    

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21. #include <machine/endian.h> 
    

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22. #define bswap_32(x) swap32(x) 
    

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23. #define bswap_64(x) swap64(x) 
    

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24. #endif 
    

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25. ---

26. #ifndef __BYTE_ORDER 
    

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27. #define __BYTE_ORDER BYTE_ORDER 
    

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28. #endif 
    

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29. #ifndef __BIG_ENDIAN 
    

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30. #define __BIG_ENDIAN BIG_ENDIAN 
    

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31. #endif 
    

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32. #ifndef __LITTLE_ENDIAN 
    

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33. #define __LITTLE_ENDIAN LITTLE_ENDIAN 
    

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34. #endif 
    

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35. ---

36. #define __u_bswap16(x) ({ uint16_t val = (x); ((uint16_t)(((val >> 8) & 0xffu) | ((val & 0xffu) << 8))); }) 
    

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37. ---

38. #if _GNUC_MIN_VER(4, 2) 
    

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39. #define __u_bswap32(x) __builtin_bswap32(x) 
    

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40. #define __u_bswap64(x) __builtin_bswap64(x) 
    

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41. #else 
    

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42. #define __u_bswap32(x) bswap_32(x) 
    

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43. #define __u_bswap64(x) bswap_64(x) 
    

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44. #endif 
    

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45. ---

46. #if __BYTE_ORDER == __LITTLE_ENDIAN 
    

    ---

47. ---

48. #define cpu_to_be64(x) __u_bswap64(x) 
    

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49. #define cpu_to_be32(x) __u_bswap32(x) 
    

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50. #define cpu_to_be16(x) __u_bswap16((uint16_t) (x)) 
    

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51. ---

52. #define be64_to_cpu(x) __u_bswap64(x) 
    

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53. #define be32_to_cpu(x) __u_bswap32(x) 
    

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54. #define be16_to_cpu(x) __u_bswap16((uint16_t) (x)) 
    

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55. ---

56. #define cpu_to_le64(x) (x) 
    

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57. #define cpu_to_le32(x) (x) 
    

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58. #define cpu_to_le16(x) (x) 
    

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59. ---

60. #define le64_to_cpu(x) (x) 
    

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61. #define le32_to_cpu(x) (x) 
    

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62. #define le16_to_cpu(x) (x) 
    

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63. ---

64. #else /* __BYTE_ORDER == __LITTLE_ENDIAN */ 
    

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65. ---

66. #define cpu_to_le64(x) __u_bswap64(x) 
    

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67. #define cpu_to_le32(x) __u_bswap32(x) 
    

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68. #define cpu_to_le16(x) __u_bswap16((uint16_t) (x)) 
    

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69. ---

70. #define le64_to_cpu(x) __u_bswap64(x) 
    

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71. #define le32_to_cpu(x) __u_bswap32(x) 
    

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72. #define le16_to_cpu(x) __u_bswap16((uint16_t) (x)) 
    

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73. ---

74. #define cpu_to_be64(x) (x) 
    

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75. #define cpu_to_be32(x) (x) 
    

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76. #define cpu_to_be16(x) (x) 
    

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77. ---

78. #define be64_to_cpu(x) (x) 
    

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79. #define be32_to_cpu(x) (x) 
    

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80. #define be16_to_cpu(x) (x) 
    

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81. ---

82. #endif 
    

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83. ---

84. #ifndef __packed 
    

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85. #define __packed __attribute__((packed)) 
    

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86. #endif 
    

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87. ---

88. #ifndef BITS_PER_LONG 
    

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89. #define BITS_PER_LONG (8 * sizeof(unsigned long)) 
    

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90. #endif 
    

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91. ---

92. static inline void bitfield_set(unsigned long *bits, int bit) 
    

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93. { 
    

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94. bits[bit / BITS_PER_LONG] |= (1UL << (bit % BITS_PER_LONG)); 
    

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95. } 
    

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96. ---

97. static inline bool bitfield_test(unsigned long *bits, int bit) 
    

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98. { 
    

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99. return !!(bits[bit / BITS_PER_LONG] & (1UL << (bit % BITS_PER_LONG))); 
    

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100. } 
     

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101. ---

102. #endif 
     

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