llcppsymg:linux compatibility

[luoliwoshang]

nm tool

dynamic symbol

using the nm tool to examine dynamic libraries, have discovered significant differences between macOS and Linux:
On Linux:

• The -D flag must be specified to obtain the corresponding symbols.
• Without -D, no symbols are displayed.

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

On macOS:

• There's no -D flag. The nm command displays all symbols (including dynamic ones) by default.

❯ nm -gDU libcjson.dylib
/Library/Developer/CommandLineTools/usr/bin/nm: error: libcjson.dylib: File format has no dynamic symbol table
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

The reason for this difference is that macOS and Linux use different formats for their executable files and handle symbol tables differently:

• Linux uses the ELF format.

• macOS uses the Mach-O format.

• xtool/nm:flags option & symbol version #829

symbol version

On Linux, symbols may appear with version declarations separated by @@
https://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html

• split version info of symbol xtool/nm:flags option & symbol version #829

dynamic lib search

pkg-config

On Linux systems, the pkg-config --libs command does not output the -L path for dynamic libraries installed in the system's default search paths

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

This output only includes the -l flag to specify the library name, but does not include the -L flag to specify the library path. This is because the library is located in the system's default search path.

will search valid path from below conf
/etc/ld.so.conf.d/*.conf
/etc/ld.so.conf

• For paths without -L,llcppsymg attempts to match and retrieve from the default search paths. llcppsymg:multiple & system dylib path search luoliwoshang/llgo#96
• About the /etc/ld.so.conf.d/*.conf 's fetch , need the os.ReadDir

so & dylib

On Linux, dynamic library names end with .so

• .so in linux,.dylib in macos

Related Bugs & Patch

• os:fix os.Errno 's nil pointer derefer in linux #828
• os.ReadDir (linux & mac)
• syscall.Faccessat (linux),cause nm can't execute