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Re: Archive (library) which overrides syscalls from toolchain's archive?

Hi Freddie,

If I want to link with my syscalls archived I get the following error:

libg.a(lib_a-sbrkr.o): In function `_sbrk_r':
newlib/newlib/libc/reent/sbrkr.c: 58: undefined reference to `_sbrk'

The problem is that my own _sbrk_r() from the archive is discarded and the
function from libg.a is used (a stub for _sbrk()).

This sounds like a linker command line ordering problem. [Aside: It would really help if you posted your linker command line ...]

What is probably happening is that your archive is being placed on the linker command line *before* the object file that calls _sbrk_r. So at the time that your archive is scanned, there are no undefined references to _sbrk_r. So it is discarded. Later on on the command line something else does call _sbrk_r, so an unresolved reference is created. Then later on still libg.a appears on the command line, this is scanned and it provides a definition of _sbrk_r. Hence the version in libg.a is pulled in. Unfortunately this version wants to call _sbrk, but no further libraries left on the command line provide that function, so the linker generates the error message above.

Is there any (possibly simple and generic) way to solve it?

Probably.  Reordering your linker command line ought to work.

or forcing _sbrk_r() to be initially undefined with
EXTERN(_sbrk_r) in the linker script, but this didn't change much.

Did you try using --undefined=_sbrk_r on the linker command line ?

Basically I'm looking for a way to just force some functions to be taken from
designated archive.

Have you tried using the --wrap linker command line option ? You could wrap calls to _sbrk_r and then provide the wrapped version in your own archive.


PS. There is also the --whole-archive linker command line option, which could be used to force all of your archive to be included in the link, but it is probably overkill.

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