Re: GDB 8.3.1 gdbserver linker error: needs -lrt

[Simon Marchi <simark@simark.ca>]

On 2020-01-30 5:17 p.m., Paul Smith wrote:
> On Thu, 2020-01-30 at 16:35 -0500, Simon Marchi wrote:
>> GDBSERVER_LIBS is a variable in gdb/gdbserver/Makefile, but I don't
>> think it's meant to be overriden from the command line.
> 
> Sure, but even if it's not meant to be overridden it should be possible
> to do so.  make always obeys variable overrides on the command line,
> and also passes those overrides along to sub-makes; the only way to
> avoid that is do to odd things with make recursion.
> 
>> It would probably work to set LIBS while configuring gdbserver:
>>
>>   ./configure LIBS="-lrt"
> 
> When you say "configuring gdbserver" I'm not sure what you mean, but
> definitely doing this in the root of the GDB distribution does not
> work.  The root makefile will have LIBS=-lrt in it, but that variable
> is not passed on.

Hmm right, the list of things passed down is explicit, and LIBS is not part
of that.  I don't really know if passing down LIBS would be the right thing
to do or not.

> Further, the link line for gdbserver doesn't include that variable;
> it's just:
> 
>   gdbserver$(EXEEXT): $(sort $(OBS)) ${CDEPS} $(LIBGNU) $(LIBIBERTY)
>         $(SILENCE) rm -f gdbserver$(EXEEXT)
>         $(ECHO_CXXLD) $(CC_LD) $(INTERNAL_CFLAGS) $(INTERNAL_LDFLAGS) \
>                 -o gdbserver$(EXEEXT) $(OBS) $(LIBGNU) $(LIBIBERTY) \
>                 $(GDBSERVER_LIBS) $(XM_CLIBS)
> 

When I suggested that, I expected that LIBS would be set in the environment
when gdbserver's configure would run, and so it would pick it up and add it
to the link line, given that `./gdb/gdbserver/configure --help` says:

  Some influential environment variables:
    ...
    LIBS        libraries to pass to the linker, e.g. -l<library>

That part seems to work.  When I do

  ./configure LIBS="-lpopt"

directly in gdbserver's source directory, popt ends up listed as:

  XM_CLIBS = -lpopt

in the generated Makefile.  XM_CLIBS is included in the link line for
gdbserver, but it's not in the IPA's.  I have no idea what XM_CLIBS stands
for.

> None of the "normal" libs variables are listed in this link line. 
> That's why I chose GDBSERVER_LIBS.
> 
> The link line for libinproctrace.so is even less configurable:
> 
>   $(IPA_LIB): $(sort $(IPA_OBJS)) ${CDEPS}
>         $(SILENCE) rm -f $(IPA_LIB)
>         $(ECHO_CXXLD) $(CC_LD) -shared -fPIC -Wl,--soname=$(IPA_LIB) \
>                 -Wl,--no-undefined $(INTERNAL_CFLAGS) $(INTERNAL_LDFLAGS) \
>                 -o $(IPA_LIB) ${IPA_OBJS} -ldl -pthread
> 
>> That would work around the problem, but if you want to fix it for
>> good, for all users in the same situation, then it would probably
>> require a patch to configure.ac, to add "-lrt" to LIBS when needed.
> 
> Yes, definitely... that's why I posted the message :).


Sorry I can't be of more help, I'm probably as (or more) confused by the
situation as you are.

Simon