Need Help to Further Reduce bsp_specs

[Sebastian Huber]

On 21/12/17 08:15, Chris Johns wrote:
> On 21/12/17 5:47 pm, Sebastian Huber wrote:
>> Hello,
>>
>> we should try to understand better why the things are how they are currently.
> Agreed.
>
>> In Newlib we have this ctr0.c:
>>
>> https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;a=blob;f=newlib/libc/sys/rtems/crt0.c;h=9778b985a180ba68990b40b6e4423aa970ca5ec7;hb=HEAD
>>
>>
>> This is the default start file for the RTEMS GCC:
>>
>> https://gcc.gnu.org/viewcvs/gcc/trunk/gcc/config/rtems.h?view=markup
>>
>>      /*
>>       * Dummy start/end specification to let linker work as
>>       * needed by autoconf scripts using this compiler.
>>       */
>>      #undef STARTFILE_SPEC
>>      #define STARTFILE_SPEC "crt0.o%s"
>>
>> We use the bsp_specs to override this (we could also use -nostartfiles at the
>> command line):
>>
>>              %rename startfile old_startfile
>>
>>              *startfile:
>>              %{!qrtems: %(old_startfile)} \
>>              %{!nostdlib: %{qrtems: crti.o%s crtbegin.o%s}}
>>
>> Why do we define a STARTFILE_SPEC in GCC which we don't use for real applications?
>>
> I good question. The gcc defaults should be focused on a user and the closer
> this is to other platforms the better.
>
>> The purpose of the ctr0.o seems to be to make the Autoconf stuff happy during
>> GCC build, e.g. for libstdc++.
> Do other build system tests, ie autoconf, require an installed BSP?

If you do link-time checks then we support currently two variants.

1. Via the Newlib ctr0.o which promises that a BSP will provide a proper 
implementation eventually (using other compiler/linker options).

2. You provide all options to link against the real BSP libraries.

The support for 1. is actually quite nice. You can build libraries per 
multilib with it.

>
>> One option would be to do this:
>>
>> 1. Change STARTFILE_SPEC:
>>
>> #undef STARTFILE_SPEC
>> #define STARTFILE_SPEC "start.o%s crti.o%s crtbegin.o"
>>
> What does a list mean?

Several startfiles. We also have endfiles.

>
>> 2. Rename Newlib ctr0.o into start.o and do NOT install it. This way it is used
>> only during GCC build to make the GCC Autoconf happy.
> OK.
>
>> 3. Provide start.o in all BSPs.
>>
>> How do we deal with other Autoconf (or other link-time feature detection) stuff?
>> This change could break all the third party library build scripts.
> I do not think this can be avoided or we can never change what we have. I do not
> like the use of -B on the gcc command line.

I think the -B switch is the only way to add search paths at the command 
line for startfiles, see "add_prefix.*startfile" in gcc/gcc.c.

-- 
Sebastian Huber, embedded brains GmbH

Address : Dornierstr. 4, D-82178 Puchheim, Germany
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E-Mail  : sebastian.huber at embedded-brains.de
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