[Qemu-devel] [RFC PATCH 1/4] configure: Improve libssh check

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

The libssh pkg-config is not complete, the libraries required to
link with libssh are not returned. For example on Ubuntu 18.04:

  $ dpkg -l|fgrep libssh
  ii libssh-4:arm64 0.8.0~20170825.94fa1e38-1ubuntu0.2 arm64 tiny C SSH library (OpenSSL flavor)
  ii libssh-dev 0.8.0~20170825.94fa1e38-1ubuntu0.2 arm64 tiny C SSH library. Development files (OpenSSL flavor)

  $ pkg-config libssh --libs
  -lssh

Since the ./configure script tries to link an object to figure if
libssh is available, it fails:

  $ cat  config.log
  [...]
  cc -pthread -I/usr/include/glib-2.0 [...] -o config-temp/qemu-conf.exe config-temp/qemu-conf.c -m64 -static -g -lssh
  /usr/lib/gcc/x86_64-linux-gnu/7/../../../x86_64-linux-gnu/libssh.a(dh.c.o): In function `ssh_crypto_init':
  (.text+0x1a9): undefined reference to `BN_new'
  (.text+0x1c2): undefined reference to `BN_set_word'
  (.text+0x1c7): undefined reference to `BN_new'
  (.text+0x1e7): undefined reference to `BN_bin2bn'
  (.text+0x1ec): undefined reference to `BN_new'
  (.text+0x20c): undefined reference to `BN_bin2bn'
  (.text+0x218): undefined reference to `OPENSSL_init_crypto'
  [...]
  collect2: error: ld returned 1 exit status

To bypass this check, simply compile an object using libssh headers.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
Should we check for libcrypto?

$ pkg-config --libs libssh openssl
-lssh -lssl -lcrypto
---
 configure | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/configure b/configure
index 714e7fb6a1..1d5c07de1f 100755
--- a/configure
+++ b/configure
@@ -3951,7 +3951,7 @@ if test "$libssh" = "yes"; then
 #include <libssh/libssh.h>
 int main(void) { return ssh_get_server_publickey(NULL, NULL); }
 EOF
-  if compile_prog "$libssh_cflags" "$libssh_libs"; then
+  if compile_object "$libssh_cflags"; then
     libssh_cflags="-DHAVE_LIBSSH_0_8 $libssh_cflags"
   fi
 fi
-- 
2.20.1