How can I extract ABI and version info from binary libs?

Zeault

Greetings,

I am trying to use crossdev to build new packages for an existing Linux system that I have a limited ability to change. The problem is I don't know what exactly my target ABI is or the different versions of the compiler and libraries that I should use.

The full story follows:

I have an older ASUS all-in-one router product which has served me well over the years, but my network is becoming more sophisticated and I need more features. Rather than replace it with a new device I would like to try and modify the firmware myself. This particular router is NOT supported by any of the open source WRT Linux distributions due to its use of proprietary Broadcom hardware and firmware. Despite that, the platform is quite open. I can access it with SSH and I have gathered a lot of system info that way. ASUS also supplies GPL source tarballs for their routers, but the one I downloaded for my model seems to be missing some files. I am still working to figure that out because it has very limited documentation, but so far I don't believe I can simply build an image using the ASUS makefiles as-is.

As for the proprietary things I can't change we have:

Some kernel modules in /lib/modules
Some programs in /bin (and maybe they use proprietary shared libs I don't know)

What I think I want to do instead of trying to build the whole image is simply extract the existing root squashfs image, add some things to it, and then write it back using mtd-write. If my (admittedly quite incomplete) knowledge of Linux is correct, then all I should need to add my own custom programs is cross build them using the same arch, ABI, kernel headers, uclibc version, and kernel version, (and compiler version?). Here lies my problem. I don't know all of these things. I'm asking to see if there is an 'easy' way I could find them out by examining the binary files that I can extract from the firmware.

This may not come off as a strictly Gentoo question, but my plan is to slowly transform this router into an embedded Gentoo system. I will use crossdev configured with all the above info to build all of the packages I want, and then I'll use the Squashfs tools to create a blob I can write to the MTD partition when I want to do an update. If I keep all the ABI and versions the same then I should be able to do this without disturbing the existing proprietary software. I just have to keep the modules and bins in their existing places right?

OH and yes for the record I am aware of the risks of messing up my router beyond repair. I am also aware that this undertaking may require a lot of expertise that I clearly don't have, but 'outside of my comfort zone' is one of my favorite places to be.

Thank you

NeddySeagoon · Posted: Tue Jun 27, 2023 5:13 pm Post subject:

Zeault,

There may be a lot of information lying around in in /proc and /var/logs

What does

pingtoo · Posted: Tue Jun 27, 2023 5:35 pm Post subject:

Zeault,

I have tendency of over engineering, So I spent a lot of time doing extra works. I wonder in this case there maybe a simpler solution.

Have you consider build static so you don't need to concern about ABI?

Depend on how much more free storage you have and what additional features you want to put on the router, if it is just simply add DHCP/DNS/PROXY you may be find a package that can easily build in statically linked binary than you don't need to care about ABI as long as you have free space to hold the binary. And with statically linked binary there maybe some other way to shrink the binary for example use app-arch/upx

GDH-gentoo · Posted: Tue Jun 27, 2023 9:46 pm Post subject:

pingtoo · Posted: Wed Jun 28, 2023 10:26 am Post subject:

Zeault · Posted: Wed Jun 28, 2023 10:45 pm Post subject:

Here is my uname

NeddySeagoon · Posted: Thu Jun 29, 2023 4:02 pm Post subject:

Zeault,

Raking about in the gentoo-x86-historical git repo

Zeault · Posted: Thu Jun 29, 2023 7:41 pm Post subject:

Oh crap. Are you implying that in order to emerge a package from portage I need to either have a more up-to-date kernel or try and find the package source from way back then? I wasn’t going to assume that everything would just work, but I thought since the kernel is mostly hardware support that I could just build the system library with those kernel headers and then almost every package could be built from the latest source. As long as it’s not some kind of low level package that needs a newer kernel feature then shouldn’t it not care what version of the kernel I have?

Like I said. A lot of expertise I clearly don’t have. But this is how I like to learn new things. Thank you for your help

NeddySeagoon · Posted: Thu Jun 29, 2023 8:34 pm Post subject:

Zeault,

If you will dynamically link things, it needs to be able to link to the installed libraries that you have on the target hardware. That means you need them in your crossdev target root.
uclibc was removed from portage by

Zeault · Posted: Thu Jun 29, 2023 9:23 pm Post subject:

Ahhh okay. I misunderstood your previous post. I think I am going to abandon the idea of linking to the existing uclibc that's on there. My new plan is to create another prefix in the squashfs and install the newest version of musl that will work with those old kernel headers. Then I can build my newish software and leave the old stuff mostly undisturbed. ....maybe. ....hopefully.

I've never made this type of musl prefix before but there is a lot of chatter about doing it across the web. e. g. people making a prefix in their home directory to compile and install software on a system they do not have administrative privileges for. I am going to try it out on a few of my other linux machines before I attempt it on the router.

Thank you very much.

pingtoo · Posted: Thu Jun 29, 2023 10:15 pm Post subject:

Zeault,

Have you try the ASUS support page for your device? I found you can download source code for your device under "Driver & Utility" Tab and select "Select OS" with "Other".

In the downloaded zip/tarball, I found in the toolchain directory have uClibc sub-directory, which in turn have 0.9.30.1 and 0.9.29 sub-directories.

The entire tarball looks to me resemble openwrt early date release source code tar ball. May be you can set up a openwrt build system or use buildroot and adopt the downloaded source code to make a complete environment.

It seems to me that there are not much of space on the internal storage, I guess it is a 32MB model it would be hard to use modern linux kernel because its size.

the "linux" partition is around 15MB, I think it is holding kernel and possible initrd.
the "rootfs" partition is around 12MB, I think you can work on this one.
the "jffs2" parition is around 576KB, I think this is where is hold your configuration changes.
the "boot" partition is is 256KB, I think it is holding u-boot.