errors
error: dereferencing pointer to incomplete type
原因：使用 typedef struct {} xxx_t 定义类型 xxx_t，定义变量时，使用 struct xxx_t ，应为 xxx_t。
1 | typedef struct xxx_s { |
找不到 libz.so.1
交叉编译时，找不到 libz.so.1，但是 sudo apt-get install zlib1g 相关的所有包都已安装。
1 | /home/sunyongfeng/workshop/rgosm-build/.toolchain-arm-cortex_a9/arm-cortex_a9/arm-cortex_a9-linux-gnueabi/bin/../lib/gcc/arm-cortex_a9-linux-gnueabi/4.4.6/../../../../arm-cortex_a9-linux-gnueabi/bin/as: error while loading shared libraries: libz.so.1: cannot open shared object file: No such file or directory |
原因：交叉编译 target 为 arm 32 bit，host 为 x64。
解决：来自 stackoverflow，安装 zlib1g:386 版本，sudo apt-get install zlib1g:i386
快速解决 -Werror 选项出错
带 -Werror 选项，一有 warning 就出错，有时不同架构间移值代码很容易出现。1
cc1: warnings being treated as errors
快速解决的方法：添加选项 -Wno-error。
-Werror 选项不生效
-Wno-error 一定要在 -Werror 之后，从实际运行看，放在后面的 option 生效。
源代码：1
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5sunyongfeng@openswitch-OptiPlex-380:~/workshop/test$ cat abc.c
int main()
{
printf("sv\n");
}
正常编译：1
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7sunyongfeng@openswitch-OptiPlex-380:~/workshop/test$ gcc -o abc abc.c
abc.c: In function ‘main’:
abc.c:3:5: warning: implicit declaration of function ‘printf’ [-Wimplicit-function-declaration]
printf("sv\n");
^
abc.c:3:5: warning: incompatible implicit declaration of built-in function ‘printf’
abc.c:3:5: note: include ‘<stdio.h>’ or provide a declaration of ‘printf’
如果 -Werror 在 -Wno-errno 之后，则 warning 还是当 error。1
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16sunyongfeng@openswitch-OptiPlex-380:~/workshop/test$ gcc -o abc abc.c -Wno-error -Werror
abc.c: In function ‘main’:
abc.c:3:5: error: implicit declaration of function ‘printf’ [-Werror=implicit-function-declaration]
printf("sv\n");
^
abc.c:3:5: error: incompatible implicit declaration of built-in function ‘printf’ [-Werror]
abc.c:3:5: note: include ‘<stdio.h>’ or provide a declaration of ‘printf’
cc1: all warnings being treated as errors
sunyongfeng@openswitch-OptiPlex-380:~/workshop/test$ gcc -o abc abc.c -Wno-error -Werror -Wno-error
abc.c: In function ‘main’:
abc.c:3:5: warning: implicit declaration of function ‘printf’ [-Wimplicit-function-declaration]
printf("sv\n");
^
abc.c:3:5: warning: incompatible implicit declaration of built-in function ‘printf’
abc.c:3:5: note: include ‘<stdio.h>’ or provide a declaration of ‘printf’
sunyongfeng@openswitch-OptiPlex-380:~/workshop/test$
库可以被找到，但是编译时还是提示 undefined reference to 'Py_Initialize'
- 问题：编译
gcc -lpython2.7 $(BUILD_CFLAGS) -o $(ELF) $^ -lxxx，libxxx.a 使用 libpython2.7.so，编译时提示找不到 python 的 symbol。 - 原因：-lxxx 写在 -lpython2.7 之后。
the linker doesn’t yet know that Py_Initialize is a required symbol when it loads libpython2.7.a, so it tosses it away. And then it gets to p.o and throws a fit about the missing symbol. Ordering it this way will let the linker look for the missing symbol in subsequent inputs.
See: http://gcc.gnu.org/onlinedocs/gcc/Link-Options.html
It makes a difference where in the command you write this option; the linker searches and processes libraries and object files in the order they are specified. Thus, foo.o -lz bar.o’ searches libraryz’ after file foo.o but before bar.o. If bar.o refers to functions in `z’, those functions may not be loaded.
- 解决：把 -lpython2.7 写在 -lxxx 之后。像这种库中依赖库的地方需要注意。
relocation R_X86_64_32 against `xxx’ can not be used when making a shared object; recompile with -fPIC sub.o: could not read symbols: Bad value
1 | x86_64-unknown-linux-gnu-gcc -fPIC -shared -D_LITTLE_ENDIAN -g -Wno-error=deprecated-declarations -Wall -D_GNU_SOURCE -lpthread |
源代码编译也添加 -fPIC 选项，在 ARM / MIPS 平台都没此问题，在 x86 才有。