Is there any way to list the files used while creating .so file? nm cannot be useful and also `readelf' also. Does some table maintain information?
readelf -s libfoobar.so | grep FILE
you cannot list the object files used to create a shared object file, since that information is not stored by default in a shared object file. A shared library is fully linked so you cannot "unarchive" it. see reference, but you can list the functions contained using this command
nm -D /usr/lib/libopenal.so.1
Related
I was shared a static library file('.a' file). When i opened it with 7z, it included two files, one without extension and one with .o extension. What are these files. Is the .o an object file here and which one of these file is actually linked during linking process.
More info about the .a file:
Lets name the file xyz.a:
When i un compress it or view it with 7z, i can see two files:
- xyz
- abc.o
The '.a' file can contain several '.o' files added by the ar utility. It can also contain an index mapping global symbols to the '.o' files that contain them. On some systems (mostly SysV or GNU based), ar's s option is used to update the index. On other systems (mostly BSD based), the index is updated by a separate ranlib utility.
To answer your questions, the '.o' files are the object (code) files that make up the library, the other file is the index, and some subset of the '.o' files will be linked by the linker, with the assistance of the index to determine which '.o' files are needed.
With the ld linker, the option -l foo would search for a dynamic library called libfoo.so or a static library called libfoo.a. Other ld options control whether it looks for a static or dynamic library and where to look for it.
I know that every header file, i.e. string.h, should have an object file in which
there is the proper implementation.
I also know that for GCC and glibc there is a libc.a or libc.so containing object files.
I tried to open libc.a to see if I could find, i.e., string.o but I didn't find it.
Why? Where can I find for every header the correspondent object file?
It may be implementation dependant. A single .h file may correspond to many .o or the opposite, you might have many .h for a single .o
For example, in my libc.a, I can see about one module per string function :
$ ar t libc.a | grep '^str' | sort
strcasecmp.o
strcasestr.o
strcat.o
strchr.o
strcmp.o
strcoll.o
strcpy.o
strcspn.o
strdup.o
strerror.o
strfmon.o
strftime.o
stringlist.o
strlcat.o
strlcpy.o
strlen.o
strmode.o
strncat.o
strncmp.o
strncpy.o
strndup.o
strnlen.o
strnstr.o
strpbrk.o
strptime.o
strrchr.o
strsep.o
strsignal.o
strspn.o
strstr.o
strtofflags.o
strtoimax.o
strtok.o
strtol.o
strtoll.o
strtonum.o
strtoq.o
strtoul.o
strtoull.o
strtoumax.o
strtouq.o
strxfrm.o
well, in my system, libc.so shows up in /lib
[sourav#braodsword temp]$ ls -l /lib/libc*
-rwxr-xr-x 1 root root 1611564 Mar 10 2010 /lib/libc-2.5.so
However, if you're looking for the source code, you'll not find that in .so file, anyway.
Again, don't expect, every header file declaration will have a defferent object file. They are taken together to form the shared library .so.
i have an executable with many .o files. i would like to reduce these object files to one file but i don't have the source code for the executable. is archiving them using "ar" is the way to do it or is it impossible without recompiling the source?
You can certainly combine the object file with ar into a library. In addition, ld -r allows to combine multiple object files into a single one.
Please tell me what it does?
$ ar -r libsldap.a
"Teach a man to fish", I say:
> man ar
[...]
DESCRIPTION
The GNU ar program creates, modifies, and extracts from archives. An
archive is a single file holding a collection of other files in a
structure that makes it possible to retrieve the original individual
files (called members of the archive).
[...]
man is your friend.
ar -r libsldap.a list-of-object-files
This line creates Linux static library, which is actually archive file that contains one or more .o files. Compiler is used previously to create these .o files.
http://www.linux.org/docs/ldp/howto/Program-Library-HOWTO/static-libraries.html
I don't really understand what ar utility does on Unix systems.
I know it can be somehow used for creating c libraries, but all that man page tells me is that it is used to make archives from files, which sounds similar to, for example, tar....
The primary purpose is to take individual object files (*.o) and bundle them together into a static library file (*.a). The .a file contains an index that allows the linker to quickly locate symbols in the library.
Tar doesn't create files that linkers understand.
ar is a general purpose archiver, just like tar. It just "happens" to be used mostly for creating static library archives, one of its traditional uses, but you can still use it for general purpose archiving, though tar would probably be a better choice. ar is also used for Debian .deb packages.
Exactly, ar is an archiver. It simply takes a set of object files (*.o) and put them in an archive that you call a static library.
It takes code in the form of object files (.obj, .o, etc) and makes a static library (archive). The library can then be included when linking with ld to include the object code into your executable.
Take a look at the example usage in the Wikipedia article.
You might want to run man ar to get the full picture. Here's a copy of that on the web.
To quote:
The GNU ar program creates, modifies, and extracts from archives. An
archive is a single file holding a collection of other files in a
structure that makes it possible to retrieve the original individual
files (called members of the archive).
ar is considered a binary utility because archives of this sort are
most often used as libraries holding commonly needed subroutines.
ar is specifically for archives (or libraries) of object code; tar is for archives of arbitrary files. Anybody's guess why GNU refers to these as 'archives', in other environments this utility is called the 'librarian', and the resulting files just libraries.