Re: [Qemu-devel] [RFC 41/48] configure: add --enable-plugins

["Alex Bennée" <alex.bennee@linaro.org>]

Emilio G. Cota <cota@braap.org> writes:

> For now only add it for ELF platforms, since we rely on the linker's
> --dynamic-list flag to pass a list of symbols to be exported to the
> executable. An alternative would be to use -rdynamic, but that would
> expose all of QEMU's objects to plugins.
>
> I have no experience with non-ELF systems but I suspect adding support
> for those should be pretty easy.
>
> Signed-off-by: Emilio G. Cota <cota@braap.org>

As far as the configure logic is concerned:

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

I'm not quite following what is so special about the dynamic-list
symbols compared to the rest of the symbols in the binary. when I do
readelf -s they are all specified as GLOBAL DEFAULT.

Perhaps this will become clearer to me once I get to the implementation
of the plugins later in the series?


> ---
>  configure | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 51 insertions(+)
>
> diff --git a/configure b/configure
> index 03bf719ca7..78e86098e5 100755
> --- a/configure
> +++ b/configure
> @@ -30,6 +30,7 @@ TMPO="${TMPDIR1}/${TMPB}.o"
>  TMPCXX="${TMPDIR1}/${TMPB}.cxx"
>  TMPE="${TMPDIR1}/${TMPB}.exe"
>  TMPMO="${TMPDIR1}/${TMPB}.mo"
> +TMPTXT="${TMPDIR1}/${TMPB}.txt"
>
>  rm -f config.log
>
> @@ -477,6 +478,7 @@ libxml2=""
>  docker="no"
>  debug_mutex="no"
>  libpmem=""
> +plugins="no"
>
>  # cross compilers defaults, can be overridden with --cross-cc-ARCH
>  cross_cc_aarch64="aarch64-linux-gnu-gcc"
> @@ -1443,6 +1445,10 @@ for opt do
>    ;;
>    --disable-libpmem) libpmem=no
>    ;;
> +  --enable-plugins) plugins="yes"
> +  ;;
> +  --disable-plugins) plugins="no"
> +  ;;
>    *)
>        echo "ERROR: unknown option $opt"
>        echo "Try '$0 --help' for more information"
> @@ -1633,6 +1639,8 @@ Advanced options (experts only):
>                             xen pv domain builder
>    --enable-debug-stack-usage
>                             track the maximum stack usage of stacks created by qemu_alloc_stack
> +  --enable-plugins
> +                           enable plugins via shared library loading
>
>  Optional features, enabled with --enable-FEATURE and
>  disabled with --disable-FEATURE, default is enabled if available:
> @@ -5204,6 +5212,42 @@ if compile_prog "" "" ; then
>    atomic64=yes
>  fi
>
> +#########################################
> +# See if --dynamic-list is supported by the linker
> +
> +cat > $TMPTXT <<EOF
> +{
> +  foo;
> +};
> +EOF
> +
> +cat > $TMPC <<EOF
> +#include <stdio.h>
> +void foo(void);
> +
> +void foo(void)
> +{
> +  printf("foo\n");
> +}
> +
> +int main(void)
> +{
> +  foo();
> +  return 0;
> +}
> +EOF
> +
> +if compile_prog "" "-Wl,--dynamic-list=$TMPTXT" ; then
> +  ld_dynamic_list="yes"
> +else
> +  if test "$plugins" = "yes" ; then
> +    error_exit \
> +        "Plugin support requires specifying a set of symbols that " \
> +        "are exported to plugins. Unfortunately your linker doesn't " \
> +        "support the flag (--dynamic-list) used for this purpose."
> +  fi
> +fi
> +
>  ########################################
>  # See if 16-byte vector operations are supported.
>  # Even without a vector unit the compiler may expand these.
> @@ -6091,6 +6135,7 @@ echo "VxHS block device $vxhs"
>  echo "capstone          $capstone"
>  echo "docker            $docker"
>  echo "libpmem support   $libpmem"
> +echo "plugin support    $plugins"
>
>  if test "$sdl_too_old" = "yes"; then
>  echo "-> Your SDL version is too old - please upgrade to have SDL support"
> @@ -6849,6 +6894,12 @@ if test "$libpmem" = "yes" ; then
>    echo "CONFIG_LIBPMEM=y" >> $config_host_mak
>  fi
>
> +if test "$plugins" = "yes" ; then
> +    echo "CONFIG_PLUGINS=y" >> $config_host_mak
> +    LIBS="-ldl $LIBS"
> +    LDFLAGS="-Wl,--dynamic-list=\$(SRC_PATH)/qemu-plugins.symbols $LDFLAGS"
> +fi
> +
>  if test "$tcg_interpreter" = "yes"; then
>    QEMU_INCLUDES="-iquote \$(SRC_PATH)/tcg/tci $QEMU_INCLUDES"
>  elif test "$ARCH" = "sparc64" ; then


--
Alex Bennée