diff --git a/crypto/bn/asm/rsaz-avx2.pl b/crypto/bn/asm/rsaz-avx2.pl
index 3b6ccf8..bbceccb 100644
--- a/crypto/bn/asm/rsaz-avx2.pl
+++ b/crypto/bn/asm/rsaz-avx2.pl
@@ -79,29 +79,13 @@
 ( $xlate="${dir}../../perlasm/x86_64-xlate.pl" and -f $xlate) or
 die "can't locate x86_64-xlate.pl";
 
-if (`$ENV{CC} -Wa,-v -c -o /dev/null -x assembler /dev/null 2>&1`
-		=~ /GNU assembler version ([2-9]\.[0-9]+)/) {
-	$avx = ($1>=2.19) + ($1>=2.22);
-	$addx = ($1>=2.23);
-}
-
-if (!$avx && $win64 && ($flavour =~ /nasm/ || $ENV{ASM} =~ /nasm/) &&
-	    `nasm -v 2>&1` =~ /NASM version ([2-9]\.[0-9]+)/) {
-	$avx = ($1>=2.09) + ($1>=2.10);
-	$addx = ($1>=2.10);
-}
-
-if (!$avx && $win64 && ($flavour =~ /masm/ || $ENV{ASM} =~ /ml64/) &&
-	    `ml64 2>&1` =~ /Version ([0-9]+)\./) {
-	$avx = ($1>=10) + ($1>=11);
-	$addx = ($1>=11);
-}
-
-if (!$avx && `$ENV{CC} -v 2>&1` =~ /(^clang version|based on LLVM) ([3-9])\.([0-9]+)/) {
-	my $ver = $2 + $3/100.0;	# 3.1->3.01, 3.10->3.10
-	$avx = ($ver>=3.0) + ($ver>=3.01);
-	$addx = ($ver>=3.03);
-}
+# In upstream, this is controlled by shelling out to the compiler to check
+# versions, but BoringSSL is intended to be used with pre-generated perlasm
+# output, so this isn't useful anyway.
+#
+# TODO(davidben): Enable these after testing. $avx goes up to 2 and $addx to 1.
+$avx = 0;
+$addx = 0;
 
 open OUT,"| \"$^X\" $xlate $flavour $output";
 *STDOUT = *OUT;
diff --git a/crypto/bn/asm/rsaz-x86_64.pl b/crypto/bn/asm/rsaz-x86_64.pl
index 3bd45db..4113d53 100644
--- a/crypto/bn/asm/rsaz-x86_64.pl
+++ b/crypto/bn/asm/rsaz-x86_64.pl
@@ -98,25 +98,12 @@
 open OUT,"| \"$^X\" $xlate $flavour $output";
 *STDOUT=*OUT;
 
-if (`$ENV{CC} -Wa,-v -c -o /dev/null -x assembler /dev/null 2>&1`
-		=~ /GNU assembler version ([2-9]\.[0-9]+)/) {
-	$addx = ($1>=2.23);
-}
-
-if (!$addx && $win64 && ($flavour =~ /nasm/ || $ENV{ASM} =~ /nasm/) &&
-	    `nasm -v 2>&1` =~ /NASM version ([2-9]\.[0-9]+)/) {
-	$addx = ($1>=2.10);
-}
-
-if (!$addx && $win64 && ($flavour =~ /masm/ || $ENV{ASM} =~ /ml64/) &&
-	    `ml64 2>&1` =~ /Version ([0-9]+)\./) {
-	$addx = ($1>=12);
-}
-
-if (!$addx && `$ENV{CC} -v 2>&1` =~ /(^clang version|based on LLVM) ([3-9])\.([0-9]+)/) {
-	my $ver = $2 + $3/100.0;	# 3.1->3.01, 3.10->3.10
-	$addx = ($ver>=3.03);
-}
+# In upstream, this is controlled by shelling out to the compiler to check
+# versions, but BoringSSL is intended to be used with pre-generated perlasm
+# output, so this isn't useful anyway.
+#
+# TODO(davidben): Enable this after testing. $addx goes up to 1.
+$addx = 0;
 
 ($out, $inp, $mod) = ("%rdi", "%rsi", "%rbp");	# common internal API
 {
diff --git a/crypto/bn/asm/x86_64-mont.pl b/crypto/bn/asm/x86_64-mont.pl
index 39476ab..04c4bea 100644
--- a/crypto/bn/asm/x86_64-mont.pl
+++ b/crypto/bn/asm/x86_64-mont.pl
@@ -53,20 +53,12 @@
 open OUT,"| \"$^X\" $xlate $flavour $output";
 *STDOUT=*OUT;
 
-if (`$ENV{CC} -Wa,-v -c -o /dev/null -x assembler /dev/null 2>&1`
-		=~ /GNU assembler version ([2-9]\.[0-9]+)/) {
-	$addx = ($1>=2.23);
-}
-
-if (!$addx && $win64 && ($flavour =~ /nasm/ || $ENV{ASM} =~ /nasm/) &&
-	    `nasm -v 2>&1` =~ /NASM version ([2-9]\.[0-9]+)/) {
-	$addx = ($1>=2.10);
-}
-
-if (!$addx && $win64 && ($flavour =~ /masm/ || $ENV{ASM} =~ /ml64/) &&
-	    `ml64 2>&1` =~ /Version ([0-9]+)\./) {
-	$addx = ($1>=12);
-}
+# In upstream, this is controlled by shelling out to the compiler to check
+# versions, but BoringSSL is intended to be used with pre-generated perlasm
+# output, so this isn't useful anyway.
+#
+# TODO(davidben): Enable this option after testing. $addx goes up to 1.
+$addx = 0;
 
 # int bn_mul_mont(
 $rp="%rdi";	# BN_ULONG *rp,
diff --git a/crypto/bn/asm/x86_64-mont5.pl b/crypto/bn/asm/x86_64-mont5.pl
index 80e9126..38def07 100644
--- a/crypto/bn/asm/x86_64-mont5.pl
+++ b/crypto/bn/asm/x86_64-mont5.pl
@@ -38,20 +38,12 @@
 open OUT,"| \"$^X\" $xlate $flavour $output";
 *STDOUT=*OUT;
 
-if (`$ENV{CC} -Wa,-v -c -o /dev/null -x assembler /dev/null 2>&1`
-		=~ /GNU assembler version ([2-9]\.[0-9]+)/) {
-	$addx = ($1>=2.23);
-}
-
-if (!$addx && $win64 && ($flavour =~ /nasm/ || $ENV{ASM} =~ /nasm/) &&
-	    `nasm -v 2>&1` =~ /NASM version ([2-9]\.[0-9]+)/) {
-	$addx = ($1>=2.10);
-}
-
-if (!$addx && $win64 && ($flavour =~ /masm/ || $ENV{ASM} =~ /ml64/) &&
-	    `ml64 2>&1` =~ /Version ([0-9]+)\./) {
-	$addx = ($1>=12);
-}
+# In upstream, this is controlled by shelling out to the compiler to check
+# versions, but BoringSSL is intended to be used with pre-generated perlasm
+# output, so this isn't useful anyway.
+#
+# TODO(davidben): Enable this after testing. $addx goes up to 1.
+$addx = 0;
 
 # int bn_mul_mont_gather5(
 $rp="%rdi";	# BN_ULONG *rp,
diff --git a/crypto/modes/asm/aesni-gcm-x86_64.pl b/crypto/modes/asm/aesni-gcm-x86_64.pl
index 7e4e04e..0ca89c7 100644
--- a/crypto/modes/asm/aesni-gcm-x86_64.pl
+++ b/crypto/modes/asm/aesni-gcm-x86_64.pl
@@ -41,24 +41,12 @@
 ( $xlate="${dir}../../perlasm/x86_64-xlate.pl" and -f $xlate) or
 die "can't locate x86_64-xlate.pl";
 
-if (`$ENV{CC} -Wa,-v -c -o /dev/null -x assembler /dev/null 2>&1`
-		=~ /GNU assembler version ([2-9]\.[0-9]+)/) {
-	$avx = ($1>=2.19) + ($1>=2.22);
-}
-
-if (!$avx && $win64 && ($flavour =~ /nasm/ || $ENV{ASM} =~ /nasm/) &&
-	    `nasm -v 2>&1` =~ /NASM version ([2-9]\.[0-9]+)/) {
-	$avx = ($1>=2.09) + ($1>=2.10);
-}
-
-if (!$avx && $win64 && ($flavour =~ /masm/ || $ENV{ASM} =~ /ml64/) &&
-	    `ml64 2>&1` =~ /Version ([0-9]+)\./) {
-	$avx = ($1>=10) + ($1>=11);
-}
-
-if (!$avx && `$ENV{CC} -v 2>&1` =~ /(^clang version|based on LLVM) ([3-9]\.[0-9]+)/) {
-	$avx = ($2>=3.0) + ($2>3.0);
-}
+# In upstream, this is controlled by shelling out to the compiler to check
+# versions, but BoringSSL is intended to be used with pre-generated perlasm
+# output, so this isn't useful anyway.
+#
+# TODO(davidben): Enable this after testing. $avx goes up to 2.
+$avx = 0;
 
 open OUT,"| \"$^X\" $xlate $flavour $output";
 *STDOUT=*OUT;
diff --git a/crypto/modes/asm/ghash-x86_64.pl b/crypto/modes/asm/ghash-x86_64.pl
index 5a7ce39..e42ca32 100644
--- a/crypto/modes/asm/ghash-x86_64.pl
+++ b/crypto/modes/asm/ghash-x86_64.pl
@@ -90,24 +90,12 @@
 ( $xlate="${dir}../../perlasm/x86_64-xlate.pl" and -f $xlate) or
 die "can't locate x86_64-xlate.pl";
 
-if (`$ENV{CC} -Wa,-v -c -o /dev/null -x assembler /dev/null 2>&1`
-		=~ /GNU assembler version ([2-9]\.[0-9]+)/) {
-	$avx = ($1>=2.19) + ($1>=2.22);
-}
-
-if (!$avx && $win64 && ($flavour =~ /nasm/ || $ENV{ASM} =~ /nasm/) &&
-	    `nasm -v 2>&1` =~ /NASM version ([2-9]\.[0-9]+)/) {
-	$avx = ($1>=2.09) + ($1>=2.10);
-}
-
-if (!$avx && $win64 && ($flavour =~ /masm/ || $ENV{ASM} =~ /ml64/) &&
-	    `ml64 2>&1` =~ /Version ([0-9]+)\./) {
-	$avx = ($1>=10) + ($1>=11);
-}
-
-if (!$avx && `$ENV{CC} -v 2>&1` =~ /(^clang version|based on LLVM) ([3-9]\.[0-9]+)/) {
-	$avx = ($2>=3.0) + ($2>3.0);
-}
+# In upstream, this is controlled by shelling out to the compiler to check
+# versions, but BoringSSL is intended to be used with pre-generated perlasm
+# output, so this isn't useful anyway.
+#
+# TODO(davidben): Enable this after testing. $avx goes up to 2.
+$avx = 0;
 
 open OUT,"| \"$^X\" $xlate $flavour $output";
 *STDOUT=*OUT;
diff --git a/crypto/perlasm/x86_64-xlate.pl b/crypto/perlasm/x86_64-xlate.pl
index 8b46329..3ebb018 100755
--- a/crypto/perlasm/x86_64-xlate.pl
+++ b/crypto/perlasm/x86_64-xlate.pl
@@ -79,22 +79,17 @@
 my $nasm=0;
 
 if    ($flavour eq "mingw64")	{ $gas=1; $elf=0; $win64=1;
+				  # TODO(davidben): Before supporting the
+				  # mingw64 perlasm flavour, do away with this
+				  # environment variable check.
+                                  die "mingw64 not supported";
 				  $prefix=`echo __USER_LABEL_PREFIX__ | $ENV{CC} -E -P -`;
 				  chomp($prefix);
 				}
 elsif ($flavour eq "macosx")	{ $gas=1; $elf=0; $prefix="_"; $decor="L\$"; }
 elsif ($flavour eq "masm")	{ $gas=0; $elf=0; $masm=$masmref; $win64=1; $decor="\$L\$"; }
 elsif ($flavour eq "nasm")	{ $gas=0; $elf=0; $nasm=$nasmref; $win64=1; $decor="\$L\$"; $PTR=""; }
-elsif (!$gas)
-{   if ($ENV{ASM} =~ m/nasm/ && `nasm -v` =~ m/version ([0-9]+)\.([0-9]+)/i)
-    {	$nasm = $1 + $2*0.01; $PTR="";  }
-    elsif (`ml64 2>&1` =~ m/Version ([0-9]+)\.([0-9]+)(\.([0-9]+))?/)
-    {	$masm = $1 + $2*2**-16 + $4*2**-32;   }
-    die "no assembler found on %PATH" if (!($nasm || $masm));
-    $win64=1;
-    $elf=0;
-    $decor="\$L\$";
-}
+elsif (!$gas)                   { die "unknown flavour $flavour"; }
 
 my $current_segment;
 my $current_function;
diff --git a/crypto/sha/asm/sha1-586.pl b/crypto/sha/asm/sha1-586.pl
index 04ccc9f..09fd3fc 100644
--- a/crypto/sha/asm/sha1-586.pl
+++ b/crypto/sha/asm/sha1-586.pl
@@ -118,21 +118,14 @@
 $xmm=$ymm=0;
 for (@ARGV) { $xmm=1 if (/-DOPENSSL_IA32_SSE2/); }
 
-$ymm=1 if ($xmm &&
-		`$ENV{CC} -Wa,-v -c -o /dev/null -x assembler /dev/null 2>&1`
-			=~ /GNU assembler version ([2-9]\.[0-9]+)/ &&
-		$1>=2.19);	# first version supporting AVX
+# In upstream, this is controlled by shelling out to the compiler to check
+# versions, but BoringSSL is intended to be used with pre-generated perlasm
+# output, so this isn't useful anyway.
+#
+# TODO(davidben): Enable this after testing. $ymm goes up to 1.
+$ymm = 0;
 
-$ymm=1 if ($xmm && !$ymm && $ARGV[0] eq "win32n" && 
-		`nasm -v 2>&1` =~ /NASM version ([2-9]\.[0-9]+)/ &&
-		$1>=2.03);	# first version supporting AVX
-
-$ymm=1 if ($xmm && !$ymm && $ARGV[0] eq "win32" &&
-		`ml 2>&1` =~ /Version ([0-9]+)\./ &&
-		$1>=10);	# first version supporting AVX
-
-$ymm=1 if ($xmm && !$ymm && `$ENV{CC} -v 2>&1` =~ /(^clang version|based on LLVM) ([3-9]\.[0-9]+)/ &&
-		$2>=3.0);	# first version supporting AVX
+$ymm = 0 unless ($xmm);
 
 $shaext=$xmm;	### set to zero if compiling for 1.0.1
 
diff --git a/crypto/sha/asm/sha1-x86_64.pl b/crypto/sha/asm/sha1-x86_64.pl
index a53f0c2..59b1607 100644
--- a/crypto/sha/asm/sha1-x86_64.pl
+++ b/crypto/sha/asm/sha1-x86_64.pl
@@ -92,24 +92,12 @@
 ( $xlate="${dir}../../perlasm/x86_64-xlate.pl" and -f $xlate) or
 die "can't locate x86_64-xlate.pl";
 
-if (`$ENV{CC} -Wa,-v -c -o /dev/null -x assembler /dev/null 2>&1`
-		=~ /GNU assembler version ([2-9]\.[0-9]+)/) {
-	$avx = ($1>=2.19) + ($1>=2.22);
-}
-
-if (!$avx && $win64 && ($flavour =~ /nasm/ || $ENV{ASM} =~ /nasm/) &&
-	   `nasm -v 2>&1` =~ /NASM version ([2-9]\.[0-9]+)/) {
-	$avx = ($1>=2.09) + ($1>=2.10);
-}
-
-if (!$avx && $win64 && ($flavour =~ /masm/ || $ENV{ASM} =~ /ml64/) &&
-	   `ml64 2>&1` =~ /Version ([0-9]+)\./) {
-	$avx = ($1>=10) + ($1>=11);
-}
-
-if (!$avx && `$ENV{CC} -v 2>&1` =~ /(^clang version|based on LLVM) ([2-9]\.[0-9]+)/) {
-	$avx = ($2>=3.0) + ($2>3.0);
-}
+# In upstream, this is controlled by shelling out to the compiler to check
+# versions, but BoringSSL is intended to be used with pre-generated perlasm
+# output, so this isn't useful anyway.
+#
+# TODO(davidben): Enable this after testing. $avx goes up to 2.
+$avx = 0;
 
 # TODO(davidben): Consider enabling the Intel SHA Extensions code once it's
 # been tested.
diff --git a/crypto/sha/asm/sha256-586.pl b/crypto/sha/asm/sha256-586.pl
index 80867d2..1866d5a 100644
--- a/crypto/sha/asm/sha256-586.pl
+++ b/crypto/sha/asm/sha256-586.pl
@@ -68,24 +68,14 @@
 $xmm=$avx=0;
 for (@ARGV) { $xmm=1 if (/-DOPENSSL_IA32_SSE2/); }
 
-if ($xmm &&	`$ENV{CC} -Wa,-v -c -o /dev/null -x assembler /dev/null 2>&1`
-			=~ /GNU assembler version ([2-9]\.[0-9]+)/) {
-	$avx = ($1>=2.19) + ($1>=2.22);
-}
+# In upstream, this is controlled by shelling out to the compiler to check
+# versions, but BoringSSL is intended to be used with pre-generated perlasm
+# output, so this isn't useful anyway.
+#
+# TODO(davidben): Enable this after testing. $avx goes up to 2.
+$avx = 0;
 
-if ($xmm && !$avx && $ARGV[0] eq "win32n" &&
-		`nasm -v 2>&1` =~ /NASM version ([2-9]\.[0-9]+)/) {
-	$avx = ($1>=2.03) + ($1>=2.10);
-}
-
-if ($xmm && !$avx && $ARGV[0] eq "win32" &&
-		`ml 2>&1` =~ /Version ([0-9]+)\./) {
-	$avx = ($1>=10) + ($1>=11);
-}
-
-if ($xmm && !$avx && `$ENV{CC} -v 2>&1` =~ /(^clang version|based on LLVM) ([3-9]\.[0-9]+)/) {
-	$avx = ($2>=3.0) + ($2>3.0);
-}
+$avx = 0 unless ($xmm);
 
 $shaext=$xmm;	### set to zero if compiling for 1.0.1
 
diff --git a/crypto/sha/asm/sha512-x86_64.pl b/crypto/sha/asm/sha512-x86_64.pl
index a7da786..9a0d0c4 100644
--- a/crypto/sha/asm/sha512-x86_64.pl
+++ b/crypto/sha/asm/sha512-x86_64.pl
@@ -109,24 +109,12 @@
 ( $xlate="${dir}../../perlasm/x86_64-xlate.pl" and -f $xlate) or
 die "can't locate x86_64-xlate.pl";
 
-if (`$ENV{CC} -Wa,-v -c -o /dev/null -x assembler /dev/null 2>&1`
-		=~ /GNU assembler version ([2-9]\.[0-9]+)/) {
-	$avx = ($1>=2.19) + ($1>=2.22);
-}
-
-if (!$avx && $win64 && ($flavour =~ /nasm/ || $ENV{ASM} =~ /nasm/) &&
-	   `nasm -v 2>&1` =~ /NASM version ([2-9]\.[0-9]+)/) {
-	$avx = ($1>=2.09) + ($1>=2.10);
-}
-
-if (!$avx && $win64 && ($flavour =~ /masm/ || $ENV{ASM} =~ /ml64/) &&
-	   `ml64 2>&1` =~ /Version ([0-9]+)\./) {
-	$avx = ($1>=10) + ($1>=11);
-}
-
-if (!$avx && `$ENV{CC} -v 2>&1` =~ /(^clang version|based on LLVM) ([3-9]\.[0-9]+)/) {
-	$avx = ($2>=3.0) + ($2>3.0);
-}
+# In upstream, this is controlled by shelling out to the compiler to check
+# versions, but BoringSSL is intended to be used with pre-generated perlasm
+# output, so this isn't useful anyway.
+#
+# TODO(davidben): Enable this after testing. $avx goes up to 2.
+$avx = 0;
 
 # TODO(davidben): Consider enabling the Intel SHA Extensions code once it's
 # been tested.