Re: avr-gcc

[Ludovic Courtès]

"Thompson, David" <address@hidden> skribis:

> On Tue, Nov 17, 2015 at 4:32 PM, Ludovic Courtès <address@hidden> wrote:

[...]

>> In GCC we modify the spec file so that the right -L/libc/dir/name is
>> passed to ld; see (gnu packages gcc), ‘GNU_USER_TARGET_LIB_SPEC’.
>>
>> However, ‘gcc-cross-sans-libc-avr’ is a bare-bones compiler, so it
>> doesn’t get the -L flag in question since there’s no libc to link to.
>>
>> To get a full-blow compiler that uses avr-libc, you could start from
>> this:
>>
>>
>>
>> … and then address any glibc assumptions you encounter.
>
> I tried to do this, but I don't really know what I'm doing.  The first
> problem I encountered was that I needed to add a case to the
> 'glibc-dynamic-linker' procedure in (gnu packages bootstrap).  I
> didn't know what ld was needed, if any, so I added this case:
>
>     ((string=? system "avr-avrlibc") "no-ld.so")

It may be that avr-libc has no dynamic linker, because it targets
MMU-less systems, no?

> Then, the issue was that avr-libc doesn't have a propagated input with
> the label "linux-headers", as required by 'cross-gcc' in (gnu packages
> cross-base).  So, as a hack I tried something like this:
>
>     (if (string=? "avr-libc" (package-name libc))
>                            `()
>                            `(("xlinux-headers" ;the target headers
>                               ,@(assoc-ref (package-propagated-inputs libc)
>                                            "linux-headers"))))
>
> Now I was able to get the build process to start, but it failed when
> trying to compile binutils:
>
>     checking target system type... Invalid configuration
> `avr-linux-avrlibc': system `avrlibc' not recognized
>
> I'm totally lost.  Any thoughts on where to go next?

Hmm, maybe my suggestion was just misguided, because the AVR environment
seems to be very different from the typical GNU/Linux environment.

For instance it’s not clear to me how as a user you’re supposed to tell
the compiler which libc.a file to choose among all those provided by
avr-libc.

Back to the Microscheme question, you could set ‘CROSS_LIBRARY_PATH’
manually to point to one of the avr/lib/xxx directories, where our
cross-gcc will find libc.a, libm.a, and crt*.o, but I don’t know if it’s
how it’s intended to work.

> BTW, I believe this native search path is needed in order for the AVR
> header files to be found:
>
>     (search-path-specification
>      (variable "C_INCLUDE_PATH")
>      (files '("avr/include")))

‘C_INCLUDE_PATH’ is the C-only equivalent of ‘CPATH’.  Our
cross-compiler honors ‘CROSS_CPATH’ instead of ‘CPATH’ so as to
distinguish between host and build headers (see
gcc-cross-environment-variables.patch.)

Also it’s not clear to me why avr-libc installs things in avr/include
instead of include/.

So in short, it looks like everything you need is already there, but the
pieces need to be wired together.  :-)

Ludo’.