[FFmpeg-devel] I have discovered why many MinGW installs can no longer build ffmpeg

[Chris Cormie]

Hi,

I'm new to ffmpeg development; hello everyone!

Back in April the ffmpeg makefiles were splendidly re-engineered by M?ns 
Rullg?rd to be non-recursive (and and much rejoicing was heard 
throughout the land, apparently.)
http://lists.mplayerhq.hu/pipermail/ffmpeg-devel/2008-April/045168.html

At the time testers reported current MinGW installs failing to build 
with the new makefiles. The poster's problem was resolved by changing 
their version of make to a specific version:  mingw32-make-3.81-2 (not 
the current version). The cause of the problem wasn't found.

I have discovered a cause: MinGW make version 3.79.1 (and earlier?) 
cannot handle calling a macro within a foreach statement. And this 
construct is used by the new non-recursive makefiles.

Specifically:
define DOSUBDIR
$(foreach V,$(SUBDIR_VARS),$(eval $(call RESET,$(V))))
SUBDIR := $(1)/
include $(1)/Makefile
endef

$(foreach D,$(FFLIBS),$(eval $(call DOSUBDIR,lib$(D))))

Fails silently (ouch) -- the include statement is never executed. The 
new system depends on the above code: the Makefiles in the 
subdirectories include the toplevel subdir.mak where the rules for 
building the libraries are located. This is why Axel Holzinger was 
reporting "make: *** No rule to make target `libavdevice/libavdevice.a', 
needed by `all'.  Stop."

This is a bit of an issue because the (complex, error prone) official 
MinGW installation instructions yield make 3.79.1

Some later versions of MinGW make can be shown not have this bug:
mingw32-make-3.81-2
make-3.81-MSYS-1.0.11-2.tar.bz2
But apparently the current release has different (breaking) bugs:
mingw32-make-3.81-20080326

This is a horrible situation for those of us trying to build ffmpeg on 
MinGW. It would be good if we could put a note about the issue somewhere 
  -- perhaps in the README? I think a lot of people could be wasting 
time over this one, given the "standard" MinGW install is affected.

I've also got a patch for configure that catches the 3.79.1 bug and 
warns the developer (below.) Could this be considered for testing and 
merging in?

Regards,
Chris Cormie

Index: configure
===================================================================
--- configure	(revision 14784)
+++ configure	(working copy)
@@ -221,7 +221,7 @@
  solving the problem.
  EOF
      fi
-    rm -f $TMPC $TMPE $TMPH $TMPO $TMPS $TMPSH
+    rm -f $TMPC $TMPE $TMPH $TMPO $TMPS $TMPSH $TMPM
      exit 1
  }

@@ -592,6 +592,13 @@
  EOF
  }

+check_make(){
+    log check_make "$@"
+    cat >$TMPM
+    log_file $TMPM
+    check_cmd make -f $TMPM
+}
+
  require(){
      name="$1"
      header="$2"
@@ -1124,6 +1131,7 @@
  TMPO="${TMPDIR1}/ffmpeg-conf-${RANDOM}-$$-${RANDOM}.o"
  TMPS="${TMPDIR1}/ffmpeg-conf-${RANDOM}-$$-${RANDOM}.S"
  TMPSH="${TMPDIR1}/ffmpeg-conf-${RANDOM}-$$-${RANDOM}.sh"
+TMPM="${TMPDIR1}/ffmpeg-conf-${RANDOM}-$$-${RANDOM}.mak"

  check_cflags -fasm
  check_cflags -std=c99
@@ -1262,6 +1270,7 @@
          SLIBNAME_WITH_MAJOR='$(SLIBPREF)$(FULLNAME).$(LIBMAJOR)$(SLIBSUF)'
          FFSERVERLDFLAGS=-Wl,-bind_at_load
          objformat="macho"
+        enabled x86_64 && objformat="macho64"
          ;;
      mingw32*)
          target_os=mingw32
@@ -1561,6 +1570,7 @@
      enabled_all x86_64 shared && append YASMFLAGS "-DPIC"
      case "$objformat" in
          elf) enabled debug && append YASMFLAGS "-g dwarf2" ;;
+        macho64)              append YASMFLAGS "-DPIC -DPREFIX" ;;
          *)                    append YASMFLAGS "-DPREFIX"  ;;
      esac
      check_yasm "pabsw xmm0, xmm0" && enable yasm
@@ -1693,6 +1703,22 @@
  EOF
  done

+# Check for broken MinGW make
+check_make <<'EOF' || die "Broken make utility. If using MinGW try a 
later version of make. make-3.81-MSYS-1.0.11-2 is known to work."
+define a
+  $(eval var = val)
+endef
+TEST_LIST = a b
+$(foreach D, $(TEST_LIST),$(eval($(call a))))
+all:
+ifeq ($(var),val)
+	@exit 0
+else
+	@exit 1
+endif
+EOF
+
+
  # these are off by default, so fail if requested and not available
  enabled avisynth   && require2 vfw32 "windows.h vfw.h" AVIFileInit -lvfw32
  enabled liba52     && require  liba52 a52dec/a52.h a52_init -la52