Re: Linker failures trying to build static qemu-user binary

[Peter Maydell]

On Thu, 9 Feb 2023 at 14:21, John Paul Adrian Glaubitz
<glaubitz@physik.fu-berlin.de> wrote:
>
> Hi!
>
> On Thu, 2023-02-09 at 14:14 +0000, Peter Maydell wrote:
> > The "Using getpwuid in statically linked applications" etc warnings
> > are expected, so we can ignore those; this is the key error:
>
> OK.
>
> > > /usr/bin/ld: /usr/lib/x86_64-linux-gnu/libdw.a(debuginfod-client.o): in 
> > > function `__libdwfl_debuginfod_init':
> > > (.text.startup+0x17): undefined reference to `dlopen'
> > > /usr/bin/ld: (.text.startup+0x32): undefined reference to `dlsym'
> > > /usr/bin/ld: (.text.startup+0x4b): undefined reference to `dlsym'
> > > /usr/bin/ld: (.text.startup+0x64): undefined reference to `dlsym'
> > > /usr/bin/ld: (.text.startup+0x7d): undefined reference to `dlsym'
> > > /usr/bin/ld: (.text.startup+0xdc): undefined reference to `dlclose'
> > > collect2: error: ld returned 1 exit status
> >
> > We use pkg-config to find out what the libdw library needs on
> > the compiler/linker command line to link successfully, so
> > maybe your distro's pkg-config info isn't right. What does
> > "pkg-config --static --libs libdw" say ?
>
> glaubitz@nofan:~> pkg-config --static --libs libdw
> -ldw -lbz2 -llzma -pthread -lpthread -lelf -lz

Right, same as my output.

> I'm building on Debian stable (Bullseye).
>
> > If libdw needs libdl
> > then it ought to list it in that output, I think. IME pkg-config
> > information is often incorrect for static linking, though.
> > I guess this one happened to work previously because glibc didn't
> > actually mandate linking with '-ldl', and now on your system it
> > apparently does. On my system pkg-config says
> > -ldw -lbz2 -llzma -pthread -lpthread -lelf -lz
> > which looks like it's missing -ldl, but the link succeeds anyway,
> > presumably because the symbols are provided by the main glibc .a.
> >
> > On the other hand, if libdw wants to use dlopen/dlsym then
> > I wonder if we should just suppress it for static linking:
> > on my (Ubuntu 22.04) ld warns:
> > /usr/bin/ld: /usr/lib/x86_64-linux-gnu/libdw.a(debuginfod-client.o):
> > in function `__libdwfl_debuginfod_init':
> > (.text.startup+0x1b): warning: Using 'dlopen' in statically linked
> > applications requires at runtime the shared libraries from the glibc
> > version used for linking
> >
> > so whatever libdw is trying to do will likely not work in most
> > statically-linked situations anyway.
>
> So, just include "-ldl" in LD_FLAGS?

If this is necessary, then pkg-config should tell us to do it :-)

But in the usual situation that you put the statically linked
QEMU binary into a chroot, the dlopen() that libdw is going to
try to do won't work anyway...

thanks
-- PMM