llcppsymg:linux

[luoliwoshang]

1. 在Linux出现了 --libs expanded后不带上动态链接库路径的问题

• 对于不存在动态链接库路径的package，均从标准库的搜索路径中再去查找一遍

root@be00d9b1c2c9:/usr/lib/aarch64-linux-gnu# pkg-config --libs lua5.4
-llua5.4 

2. Linux上动态链接库名称为 .so 结尾，并且nm工具对于linux上apt-get 获得的动态链接库获取不了其符号信息

root@be00d9b1c2c9:/lib/aarch64-linux-gnu# ldconfig -p | grep lua5.4   
        liblua5.4.so.0 (libc6,AArch64) => /lib/aarch64-linux-gnu/liblua5.4.so.0
        liblua5.4.so (libc6,AArch64) => /lib/aarch64-linux-gnu/liblua5.4.so
        liblua5.4-c++.so.0 (libc6,AArch64) => /lib/aarch64-linux-gnu/liblua5.4-c++.so.0
        liblua5.4-c++.so (libc6,AArch64) => /lib/aarch64-linux-gnu/liblua5.4-c++.so

root@be00d9b1c2c9:/lib/aarch64-linux-gnu# ls | grep "lua"
liblua5.4-c++.a
liblua5.4-c++.so
liblua5.4-c++.so.0
liblua5.4-c++.so.0.0.0
liblua5.4.a
liblua5.4.so
liblua5.4.so.0
liblua5.4.so.0.0.0
root@be00d9b1c2c9:/lib/aarch64-linux-gnu# nm liblua5.4.so
nm: liblua5.4.so: no symbols
root@be00d9b1c2c9:/lib/aarch64-linux-gnu# nm liblua5.4.so.0
nm: liblua5.4.so.0: no symbols
root@be00d9b1c2c9:/lib/aarch64-linux-gnu# nm liblua5.4.so.0.0.0
nm: liblua5.4.so.0.0.0: no symbols

[luoliwoshang]

https://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html

[luoliwoshang]

https://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html

Linux 上Symbol会出现用@@声明版本，分割的符号

root@be00d9b1c2c9:/lib/aarch64-linux-gnu# nm -gDU liblua5.4.so
0000000000000000 A LUA_5.4
0000000000026a40 T luaL_addgsub@@LUA_5.4
00000000000269a0 T luaL_addlstring@@LUA_5.4
0000000000026a04 T luaL_addstring@@LUA_5.4
0000000000026b80 T luaL_addvalue@@LUA_5.4
0000000000023624 T luaL_argerror@@LUA_5.4
0000000000024100 T luaL_buffinit@@LUA_5.4

[luoliwoshang]

对于nm工具来说，发现在macos上必须不指定-D 输出，在linux上必须指定-D才能获得对应的符号

linux

root@be00d9b1c2c9:/lib/aarch64-linux-gnu# nm -gU liblua5.4.so
nm: liblua5.4.so: no symbols

root@be00d9b1c2c9:/lib/aarch64-linux-gnu# nm -gDU liblua5.4.so
0000000000000000 A LUA_5.4
0000000000026a40 T luaL_addgsub@@LUA_5.4
00000000000269a0 T luaL_addlstring@@LUA_5.4
0000000000026a04 T luaL_addstring@@LUA_5.4

macos

homebrew/lib on  stable via  v21.7.2 
❯ nm -gU libcjson.dylib
0000000000002ab8 T _cJSON_AddArrayToObject
0000000000002720 T _cJSON_AddBoolToObject
0000000000002690 T _cJSON_AddFalseToObject
0000000000002440 T _cJSON_AddItemReferenceToArray
0000000000002520 T _cJSON_AddItemReferenceToObject

homebrew/lib on  stable via  v21.7.2 
❯ nm -gDU libcjson.dylib
/Library/Developer/CommandLineTools/usr/bin/nm: error: libcjson.dylib: File format has no dynamic symbol table

原因是macOS 和 Linux 在动态库的结构和符号表管理存在不同，Linux 采用 ELF 格式，而macOS 采用Mach-O 格式

通过 Macos的报错可以看到，这个文件格式不存在动态符号表,并且通过 man nm来查看也不存在-D 选项