[PATCH v2 1/2] meson: Add missing libdw knobs

[PATCH v2 1/2] meson: Add missing libdw knobs

[Ilya Leoshkevich]

Add the missing meson infrastructure bits for the new libdw
dependency. Model them after the existing capstone knobs.

Fixes: 7c10cb38ccb8 ("accel/tcg: Add debuginfo support")
Reported-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
---
 meson.build                   | 11 +++++++----
 meson_options.txt             |  2 ++
 scripts/meson-buildoptions.sh |  3 +++
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/meson.build b/meson.build
index 4ba3bf34317..87bc720f912 100644
--- a/meson.build
+++ b/meson.build
@@ -1649,10 +1649,13 @@ if libbpf.found() and not cc.links('''
 endif
 
 # libdw
-libdw = dependency('libdw',
-                   method: 'pkg-config',
-                   kwargs: static_kwargs,
-                   required: false)
+libdw = not_found
+if not get_option('libdw').auto() or have_system or have_user
+    libdw = dependency('libdw',
+                       method: 'pkg-config',
+                       kwargs: static_kwargs,
+                       required: get_option('libdw'))
+endif
 
 #################
 # config-host.h #
diff --git a/meson_options.txt b/meson_options.txt
index 559a571b6b6..082ce437ba5 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -129,6 +129,8 @@ option('gio', type : 'feature', value : 'auto',
        description: 'use libgio for D-Bus support')
 option('glusterfs', type : 'feature', value : 'auto',
        description: 'Glusterfs block device driver')
+option('libdw', type : 'feature', value : 'auto',
+       description: 'debuginfo support')
 option('libiscsi', type : 'feature', value : 'auto',
        description: 'libiscsi userspace initiator')
 option('libnfs', type : 'feature', value : 'auto',
diff --git a/scripts/meson-buildoptions.sh b/scripts/meson-buildoptions.sh
index 0f71e92dcba..e5a8897b639 100644
--- a/scripts/meson-buildoptions.sh
+++ b/scripts/meson-buildoptions.sh
@@ -108,6 +108,7 @@ meson_options_help() {
   printf "%s\n" '  kvm             KVM acceleration support'
   printf "%s\n" '  l2tpv3          l2tpv3 network backend support'
   printf "%s\n" '  libdaxctl       libdaxctl support'
+  printf "%s\n" '  libdw           debuginfo support'
   printf "%s\n" '  libiscsi        libiscsi userspace initiator'
   printf "%s\n" '  libnfs          libnfs block device driver'
   printf "%s\n" '  libpmem         libpmem support'
@@ -308,6 +309,8 @@ _meson_option_parse() {
     --disable-l2tpv3) printf "%s" -Dl2tpv3=disabled ;;
     --enable-libdaxctl) printf "%s" -Dlibdaxctl=enabled ;;
     --disable-libdaxctl) printf "%s" -Dlibdaxctl=disabled ;;
+    --enable-libdw) printf "%s" -Dlibdw=enabled ;;
+    --disable-libdw) printf "%s" -Dlibdw=disabled ;;
     --libdir=*) quote_sh "-Dlibdir=$2" ;;
     --libexecdir=*) quote_sh "-Dlibexecdir=$2" ;;
     --enable-libiscsi) printf "%s" -Dlibiscsi=enabled ;;
-- 
2.39.1

[PATCH v2 2/2] meson: Disable libdw for static builds by default

[Ilya Leoshkevich]

Static QEMU build fails on Debian Bullseye:

    /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'

The reason is that pkg-config does not suggest -ldl for libdw, and
adding --extra-ldflags="-ldl" resolves the issue. However, static
linking with libdw is an unclear topic:

* Linux perf does it.
* Debian's libdw-dev description says:

      Only link to the static version for special cases and when you
      don't need anything from the ebl backends.

* As the error message above indicates, -ldl is also needed for
  debuginfod support.

The functionality provided by libdw is needed for analyzing performance
of JITed code, which is mostly useful to developers and researchers.
Therefore, in order to avoid unpleasant surprises for people who don't
need this, simply disable libdw for static builds by default. It can
still be enabled explicitly if needed.

Reported-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 meson.build | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/meson.build b/meson.build
index 87bc720f912..9bd6278f268 100644
--- a/meson.build
+++ b/meson.build
@@ -1650,7 +1650,8 @@ endif
 
 # libdw
 libdw = not_found
-if not get_option('libdw').auto() or have_system or have_user
+if not get_option('libdw').auto() or \
+        (not enable_static and (have_system or have_user))
     libdw = dependency('libdw',
                        method: 'pkg-config',
                        kwargs: static_kwargs,
-- 
2.39.1