--- a/build/moz.configure/init.configure
+++ b/build/moz.configure/init.configure
@@ -262,16 +262,17 @@ def wanted_mozconfig_variables(help):
          'MOZ_INSTRUMENT_EVENT_LOOP',
          'PERL',
          'RPMBUILD',
          'TAR',
          'UNZIP',
          'USE_FC_FREETYPE',
          'WITHOUT_X',
          'XARGS',
+         'YASM',
          'ZIP',
      ])
 
 
 @depends(mozconfig, wanted_mozconfig_variables)
 def mozconfig_options(mozconfig, wanted_mozconfig_variables):
     if mozconfig['path']:
         helper = command_line_helper()

--- a/config/config.mk
+++ b/config/config.mk
@@ -133,17 +133,17 @@ TOUCH ?= touch
 PYTHON_PATH = $(PYTHON) $(topsrcdir)/config/pythonpath.py
 
 # determine debug-related options
 _DEBUG_ASFLAGS :=
 _DEBUG_CFLAGS :=
 _DEBUG_LDFLAGS :=
 
 ifneq (,$(MOZ_DEBUG)$(MOZ_DEBUG_SYMBOLS))
-  ifeq ($(AS),yasm)
+  ifeq ($(AS),$(YASM))
     ifeq ($(OS_ARCH)_$(GNU_CC),WINNT_)
       _DEBUG_ASFLAGS += -g cv8
     else
       ifneq ($(OS_ARCH),Darwin)
         _DEBUG_ASFLAGS += -g dwarf2
       endif
     endif
   else

--- a/moz.configure
+++ b/moz.configure
@@ -106,16 +106,60 @@ def perl_version_check(min_version):
     def require_full_perl_installation(has_full_perl_installation):
         if not has_full_perl_installation:
             error('Cannot find Config.pm or $Config{archlib}. '
                   'A full perl installation is required.')
 
 perl_version_check('5.006')
 
 
+# yasm detection
+# ==============================================================
+yasm = check_prog('YASM', ['yasm'], allow_missing=True)
+
+@depends(yasm)
+@checking('yasm version')
+@advanced
+def yasm_version(yasm):
+    if yasm:
+        import subprocess
+        try:
+            version = Version(subprocess.check_output(
+                [yasm, '--version']
+            ).splitlines()[0].split()[1])
+            # Until we move all the yasm consumers out of old-configure.
+            add_old_configure_assignment('_YASM_MAJOR_VERSION', version[0])
+            add_old_configure_assignment('_YASM_MINOR_VERSION', version[1])
+            return version
+        except subprocess.CalledProcessError as e:
+            error('Failed to get yasm version: %s' % e.message)
+
+@depends(yasm, target)
+def yasm_asflags(yasm, target):
+    if yasm:
+        asflags = {
+            ('OSX', 'x86'): '-f macho32 -rnasm -pnasm',
+            ('OSX', 'x86_64'): '-f macho64 -rnasm -pnasm',
+            ('WINNT', 'x86'): '-f win32 -rnasm -pnasm',
+            ('WINNT', 'x86_64'): '-f x64 -rnasm -pnasm',
+        }.get((target.os, target.cpu), None)
+        if asflags is None:
+            # We're assuming every x86 platform we support that's
+            # not Windows or Mac is ELF.
+            if target.cpu == 'x86':
+                asflags = '-f elf32 -rnasm -pnasm'
+            elif target.cpu == 'x86_64':
+                asflags = '-f elf64 -rnasm -pnasm'
+        if asflags:
+            set_config('YASM_ASFLAGS', asflags)
+            set_config('HAVE_YASM', '1')
+            # Until the YASM variable is not necessary in old-configure.
+            add_old_configure_assignment('YASM', '1')
+        return asflags
+
 # Miscellaneous programs
 # ==============================================================
 check_prog('DOXYGEN', ('doxygen',), allow_missing=True)
 check_prog('TAR', ('gnutar', 'gtar', 'tar'))
 check_prog('UNZIP', ('unzip',))
 check_prog('XARGS', ('xargs',))
 check_prog('ZIP', ('zip',))
 

--- a/old-configure.in
+++ b/old-configure.in
@@ -2788,69 +2788,16 @@ if test -n "$_USE_SYSTEM_NSS"; then
 fi
 
 if test -n "$MOZ_SYSTEM_NSS"; then
    NSS_LIBS="$NSS_LIBS -lcrmf"
 else
    NSS_CFLAGS="-I${DIST}/include/nss"
 fi
 
-dnl ======================
-dnl Detect yasm
-dnl ======================
-
-AC_MSG_CHECKING([for YASM assembler])
-AC_CHECK_PROGS(YASM, yasm, "")
-
-if test -n "$YASM"; then
-  AC_MSG_CHECKING([yasm version])
-  dnl Pull out yasm's version string
-  YASM_VERSION=`yasm --version | $AWK '/^yasm/ { print $2 }'`
-  _YASM_MAJOR_VERSION=`echo ${YASM_VERSION} | $AWK -F\. '{ print $1 }'`
-  _YASM_MINOR_VERSION=`echo ${YASM_VERSION} | $AWK -F\. '{ print $2 }'`
-  _YASM_RELEASE=`      echo ${YASM_VERSION} | $AWK -F\. '{ print $3 }'`
-  _YASM_BUILD=`        echo ${YASM_VERSION} | $AWK -F\. '{ print $4 }'`
-  AC_MSG_RESULT([$_YASM_MAJOR_VERSION.$_YASM_MINOR_VERSION.$_YASM_RELEASE ($YASM_VERSION)])
-
-  # Determine proper yasm arguments.
-  YASM_ASFLAGS=
-  case "$OS_ARCH:$CPU_ARCH" in
-    Darwin:x86)
-      YASM_ASFLAGS="-f macho32 -rnasm -pnasm"
-    ;;
-    Darwin:x86_64)
-      YASM_ASFLAGS="-f macho64 -rnasm -pnasm"
-    ;;
-    WINNT:x86_64)
-      YASM_ASFLAGS="-f x64 -rnasm -pnasm"
-    ;;
-    WINNT:x86)
-      YASM_ASFLAGS="-f win32 -rnasm -pnasm"
-    ;;
-    *:x86)
-      if $CC -E -dM -</dev/null | grep -q __ELF__; then
-        YASM_ASFLAGS="-f elf32 -rnasm -pnasm"
-      fi
-    ;;
-    *:x86_64)
-      if $CC -E -dM -</dev/null | grep -q __ELF__; then
-        YASM_ASFLAGS="-f elf64 -rnasm -pnasm"
-      fi
-    ;;
-    *)
-      # yasm doesn't support other architectures, so just disable it.
-      YASM=
-  esac
-  if test -z "$YASM_ASFLAGS"; then
-    # If we didn't get YASM_ASFLAGS, we shouldn't be using yasm.
-    YASM=
-  fi
-fi
-AC_SUBST(YASM_ASFLAGS)
-
 if test -z "$SKIP_LIBRARY_CHECKS"; then
 dnl system JPEG support
 dnl ========================================================
 MOZ_ARG_WITH_STRING(system-jpeg,
 [  --with-system-jpeg[=PFX]
                           Use system libjpeg [installed at prefix PFX]],
     JPEG_DIR=$withval)