[En-Nut-Discussion] CM4: Linking external (crypto) library

[Matthias Ringwald]

Hi Philipp

I have no experience with libsodium or your actual linker issue.

When looking for a library for ECC, NaCl / libsodium seemed not suited for embedded (I guess I was wrong about that).
Then, I've tried mbedTLS. That worked for me but mbedTLS requires malloc. I created a minimal malloc implementation, just for mbedTLS, but it required more RAM that I've liked.

Finally, I came across micro-ecc (https://github.com/kmackay/micro-ecc). It's malloc-free and works well. Maybe it is suitable for your setup as well.

Best
 Matthias

> On 2 Mar 2019, at 17:35, Philipp Burch <phip at hb9etc.ch> wrote:
> 
> Anyone?
> 
> Regards,
> Philipp
> 
> On 08.02.19 14:54, Philipp Burch wrote:
>> Hi everyone,
>> 
>> I'm on the way to add encryption and signature support to the
>> tiva_ethloader bootloader (see https://hb9etc.ch/hg/tiva_ethloader/). As
>> a start, I looked for a suitable crypto library to do the hard work,
>> which provides support for (symmetric) encryption and (asymmetric)
>> signature checking. As it is planned right now, there should be no need
>> for a random number generator on the device, so it really is only a
>> software thing.
>> 
>> I know that Ethernut already has some kind of crypto library included,
>> but haven't looked closely at it yet. In the configurator, I see that
>> AES is mentioned, but haven't seen anything that provides signature
>> checking (could be RSA-based, or even better some EC cryptography to get
>> away with shorter keys). Correct me, if I'm wrong. I'll happily use some
>> existing Ethernut code if it already includes what I need.
>> 
>> Anyway, as the topic suggests, I'm actually trying to get an external
>> lib included in my code, libsodium
>> (https://github.com/jedisct1/libsodium) to be exact. Compilation of the
>> library itself for the arm-none-eabi target is quite easy and gives me
>> the libsodium.a for inclusion.
>> 
>> Now, when trying to add the library to the bootloader, the linker coughs
>> because of multiple definitions of fflush() and also due to undefined
>> references to some underlying functions like _close() and _read():
>> 
>> ------- 8< ------- 8< -------
>> 
>> /usr/bin/../lib/gcc/arm-none-eabi/7.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m/fpv4-sp/hard/libc.a(lib_a-fflush.o):
>> In function `fflush':
>> fflush.c:(.text.fflush+0x0): multiple definition of `fflush'
>> /home/phip/phipsfiles/developing/ethernut/nutinstall-fpm_01b/libnutcrt.a(fflush.o):fflush.c:(.text.fflush+0x0):
>> first defined here
>> /usr/bin/../lib/gcc/arm-none-eabi/7.3.1/../../../../arm-none-eabi/bin/ld:
>> section .ARM.exidx LMA [000000000001e0e0,000000000001e0e7] overlaps
>> section .data LMA [000000000001e0e0,000000000001f1d7]
>> /usr/bin/../lib/gcc/arm-none-eabi/7.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m/fpv4-sp/hard/libc.a(lib_a-closer.o):
>> In function `_close_r':
>> closer.c:(.text._close_r+0xc): undefined reference to `_close'
>> /usr/bin/../lib/gcc/arm-none-eabi/7.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m/fpv4-sp/hard/libc.a(lib_a-readr.o):
>> In function `_read_r':
>> readr.c:(.text._read_r+0x12): undefined reference to `_read'
>> /usr/bin/../lib/gcc/arm-none-eabi/7.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m/fpv4-sp/hard/libc.a(lib_a-fstatr.o):
>> In function `_fstat_r':
>> fstatr.c:(.text._fstat_r+0x10): undefined reference to `_fstat'
>> /usr/bin/../lib/gcc/arm-none-eabi/7.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m/fpv4-sp/hard/libc.a(lib_a-isattyr.o):
>> In function `_isatty_r':
>> isattyr.c:(.text._isatty_r+0xc): undefined reference to `_isatty'
>> /usr/bin/../lib/gcc/arm-none-eabi/7.3.1/../../../../arm-none-eabi/lib/thumb/v7e-m/fpv4-sp/hard/libc.a(lib_a-lseekr.o):
>> In function `_lseek_r':
>> lseekr.c:(.text._lseek_r+0x12): undefined reference to `_lseek'
>> 
>> ------- 8< ------- 8< -------
>> 
>> According to the paths, this is because the linker takes code from ARM's
>> standard library, instead of the one included in Ethernut.
>> 
>> Now the question: How can I find out what symbol triggers the inclusion
>> of the ARM standard library? And how can I fix this? I already tried
>> various compiler flags when compiling libsodium, also the ones that are
>> used when compiling the Ethernut libs or the bootloader itself, but
>> without luck, the errors stay the same.
>> 
>> I'd be glad for any hints!
>> 
>> Thanks and regards,
>> Philipp
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