如何判断编译时glibc中某个宏在哪里定义的？

Question

我在编译native u-boot的时候，碰到vdprintf没有定义的问题，后来发现是因为宏__USE_XOPEN2K8没有打开的原因，但是这个宏只在glibc中使用了，u-boot并没有使用它，而且应不应该去使用它。如果使用交叉编译器没有这样的问题，__USE_XOPEN2K8似乎被定义了。那么我如何检查这个宏到底是在哪里定义的呢？gcc会传递一些缺省宏吧？glibc也有一些宏是打开的。有没有办法可以列出编译过程中哪些宏被打开了？

Answer 1

谢谢，真得很有用

Answer 2

2. [root@mail ~/gcc-3.0/build/gcc]# cat 1.c
3. #define A 1
4. #undef A
6. [root@mail ~/gcc-3.0/build/gcc]# gcc -E -dD 1.c
7. # 1 "1.c"
8. # 1 "<built-in>"
9. #define __VERSION__ "3.2.2 20030222 (Red Hat Linux 3.2.2-5)"
10. #define __USER_LABEL_PREFIX__
11. #define __REGISTER_PREFIX__
12. #define __HAVE_BUILTIN_SETJMP__ 1
13. #define __SIZE_TYPE__ unsigned int
14. #define __PTRDIFF_TYPE__ int
15. #define __WCHAR_TYPE__ long int
16. #define __WINT_TYPE__ unsigned int
17. #define __STDC__ 1
18. # 1 "<command line>"
19. #define __GNUC__ 3
20. # 1 "<command line>"
21. #define __GNUC_MINOR__ 2
22. # 1 "<command line>"
23. #define __GNUC_PATCHLEVEL__ 2
24. # 1 "<command line>"
25. #define __GXX_ABI_VERSION 102
26. # 1 "<command line>"
27. #define __ELF__ 1
28. # 1 "<command line>"
29. #define unix 1
30. # 1 "<command line>"
31. #define __gnu_linux__ 1
32. # 1 "<command line>"
33. #define linux 1
34. # 1 "<command line>"
35. #define __ELF__ 1
36. # 1 "<command line>"
37. #define __unix__ 1
38. # 1 "<command line>"
39. #define __gnu_linux__ 1
40. # 1 "<command line>"
41. #define __linux__ 1
42. # 1 "<command line>"
43. #define __unix 1
44. # 1 "<command line>"
45. #define __linux 1
46. # 1 "<command line>"
47. #define __NO_INLINE__ 1
48. # 1 "<command line>"
49. #define __STDC_HOSTED__ 1
50. # 1 "<command line>"
51. #define i386 1
52. # 1 "<command line>"
53. #define __i386 1
54. # 1 "<command line>"
55. #define __i386__ 1
56. # 1 "<command line>"
57. #define __tune_i386__ 1
58. # 1 "1.c"
59. #define A 1
60. #undef A
61. [root@mail ~/gcc-3.0/build/gcc]# gcc -E -dM 1.c
62. #define __HAVE_BUILTIN_SETJMP__ 1
63. #define __unix__ 1
64. #define unix 1
65. #define __i386__ 1
66. #define __SIZE_TYPE__ unsigned int
67. #define __ELF__ 1
68. #define __GNUC_PATCHLEVEL__ 2
69. #define __linux 1
70. #define __unix 1
71. #define __linux__ 1
72. #define __USER_LABEL_PREFIX__
73. #define linux 1
74. #define __STDC_HOSTED__ 1
75. #define __WCHAR_TYPE__ long int
76. #define __gnu_linux__ 1
77. #define __WINT_TYPE__ unsigned int
78. #define __GNUC__ 3
79. #define __GXX_ABI_VERSION 102
80. #define i386 1
81. #define __GNUC_MINOR__ 2
82. #define __STDC__ 1
83. #define __PTRDIFF_TYPE__ int
84. #define __tune_i386__ 1
85. #define __REGISTER_PREFIX__
86. #define __NO_INLINE__ 1
87. #define __i386 1
88. #define __VERSION__ "3.2.2 20030222 (Red Hat Linux 3.2.2-5)"

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