[GDB] 載入某個 library 的 symbol file
今天用 gdb debug 一個 crash dump，backtrace 裡什麼都看不到：
(gdb) bt #0 0x00007f4d3fbb23e2 in ?? () #1 0x000000000298f970 in ?? () #2 0x000000000298f97c in ?? () #3 0x000000000298f978 in ?? () #4 0x0000000000000000 in ?? ()
想想應該是因為程式裡用到的 share library 的 debug symbol 被我們拔掉了～
先用 info sharedlibrary 查一下各個 library 的載入位址，
如本例中的 ../libmy.so 是在 0x00007f4d3fb942b0：
(gdb) info sharedlibrary From To Syms Read Shared Object Library 0x00007f4d3fff9670 0x00007f4d40002ae8 No /lib64/lib7zip.so.0 0x00007f4d3fdd48a0 0x00007f4d3fddf514 No /lib64/libpthread.so.0 0x00007f4d3fb942b0 0x00007f4d3fbb5604 No ../libmy.so 0x00007f4d3f8ab510 0x00007f4d3f91259a No /lib64/libstdc++.so.6 0x00007f4d3f5534b0 0x00007f4d3f5bd9e8 No /lib64/libm.so.6 0x00007f4d3f33aaf0 0x00007f4d3f34a298 No /lib64/libgcc_s.so.1 0x00007f4d3ef963e0 0x00007f4d3f0d9ba0 No /lib64/libc.so.6 0x00007f4d4020aae0 0x00007f4d4022527a No /lib64/ld-linux-x86-64.so.2 0x00007f4d3ed73ed0 0x00007f4d3ed749d0 No /lib64/libdl.so.2 0x00007f4d3aadf570 0x00007f4d3aae0018 No /usr/lib64/gconv/ISO8859-1.so
接著就可以用 add-symbol-file 指令，直接指定 symbol file 要載入到哪個位址去：
(gdb) add-symbol-file ../libmy.so.dbg 0x00007f4d3fb942b0 add symbol table from file "../libmy.so.dbg" at .text_addr = 0x7f4d3fb942b0 (y or n) y Reading symbols from /tmp/libmy.so.dbg...done.
載入好後，backtrace 就可以看到 shared library 的 symbol 囉：
(gdb) bt #0 0x00007f4d3fbb23e2 in NormalizeFileType (this=<error reading variable: can't compute CFA for this frame>, nFileType=<error reading variable: can't compute CFA for this frame>) at ./Manager.cpp:12 #1 0x00007f4d3fb9fb17 in AddFile (this=<error reading variable: can't compute CFA for this frame>, pFileName=<error reading variable: can't compute CFA for this frame>) at ./Scan.cpp:638 #2 0x000000000042093e in ?? () #3 0x00007ffd3ea26328 in ?? () #4 0x0000000000000000 in ?? ()
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