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

[Philipp Burch]

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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