diff --git a/crypto/bn/asm/rsaz-avx2.pl b/crypto/bn/asm/rsaz-avx2.pl
index e7af78b..3b6ccf8 100644
--- a/crypto/bn/asm/rsaz-avx2.pl
+++ b/crypto/bn/asm/rsaz-avx2.pl
@@ -79,11 +79,29 @@
 ( $xlate="${dir}../../perlasm/x86_64-xlate.pl" and -f $xlate) or
 die "can't locate x86_64-xlate.pl";
 
-# 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.
-$avx = 2;
-$addx = 1;
+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);
+}
 
 open OUT,"| \"$^X\" $xlate $flavour $output";
 *STDOUT = *OUT;
diff --git a/crypto/bn/asm/rsaz-x86_64.pl b/crypto/bn/asm/rsaz-x86_64.pl
index 075cf2b..3bd45db 100644
--- a/crypto/bn/asm/rsaz-x86_64.pl
+++ b/crypto/bn/asm/rsaz-x86_64.pl
@@ -98,10 +98,25 @@
 open OUT,"| \"$^X\" $xlate $flavour $output";
 *STDOUT=*OUT;
 
-# 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.
-$addx = 1;
+if (`$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);
+}
 
 ($out, $inp, $mod) = ("%rdi", "%rsi", "%rbp");	# common internal API
 {
diff --git a/crypto/bn/asm/x86_64-mont.pl b/crypto/bn/asm/x86_64-mont.pl
index 59ce088..39476ab 100644
--- a/crypto/bn/asm/x86_64-mont.pl
+++ b/crypto/bn/asm/x86_64-mont.pl
@@ -53,10 +53,20 @@
 open OUT,"| \"$^X\" $xlate $flavour $output";
 *STDOUT=*OUT;
 
-# 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.
-$addx = 1;
+if (`$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);
+}
 
 # int bn_mul_mont(
 $rp="%rdi";	# BN_ULONG *rp,
diff --git a/crypto/bn/asm/x86_64-mont5.pl b/crypto/bn/asm/x86_64-mont5.pl
index e3d92e8..80e9126 100644
--- a/crypto/bn/asm/x86_64-mont5.pl
+++ b/crypto/bn/asm/x86_64-mont5.pl
@@ -38,10 +38,20 @@
 open OUT,"| \"$^X\" $xlate $flavour $output";
 *STDOUT=*OUT;
 
-# 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.
-$addx = 1;
+if (`$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);
+}
 
 # 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 e6ad694..7e4e04e 100644
--- a/crypto/modes/asm/aesni-gcm-x86_64.pl
+++ b/crypto/modes/asm/aesni-gcm-x86_64.pl
@@ -41,10 +41,24 @@
 ( $xlate="${dir}../../perlasm/x86_64-xlate.pl" and -f $xlate) or
 die "can't locate x86_64-xlate.pl";
 
-# 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.
-$avx = 2;
+if (`$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);
+}
 
 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 d1720d9..5a7ce39 100644
--- a/crypto/modes/asm/ghash-x86_64.pl
+++ b/crypto/modes/asm/ghash-x86_64.pl
@@ -90,10 +90,24 @@
 ( $xlate="${dir}../../perlasm/x86_64-xlate.pl" and -f $xlate) or
 die "can't locate x86_64-xlate.pl";
 
-# 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.
-$avx = 2;
+if (`$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);
+}
 
 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 3ebb018..8b46329 100755
--- a/crypto/perlasm/x86_64-xlate.pl
+++ b/crypto/perlasm/x86_64-xlate.pl
@@ -79,17 +79,22 @@
 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)                   { die "unknown flavour $flavour"; }
+elsif (!$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\$";
+}
 
 my $current_segment;
 my $current_function;
diff --git a/crypto/sha/asm/sha1-586.pl b/crypto/sha/asm/sha1-586.pl
index ec5b105..04ccc9f 100644
--- a/crypto/sha/asm/sha1-586.pl
+++ b/crypto/sha/asm/sha1-586.pl
@@ -118,10 +118,21 @@
 $xmm=$ymm=0;
 for (@ARGV) { $xmm=1 if (/-DOPENSSL_IA32_SSE2/); }
 
-# 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.
-$ymm = 1 if ($xmm);
+$ymm=1 if ($xmm &&
+		`$ENV{CC} -Wa,-v -c -o /dev/null -x assembler /dev/null 2>&1`
+			=~ /GNU assembler version ([2-9]\.[0-9]+)/ &&
+		$1>=2.19);	# first version supporting AVX
+
+$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
 
 $shaext=$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 66a338f..a53f0c2 100644
--- a/crypto/sha/asm/sha1-x86_64.pl
+++ b/crypto/sha/asm/sha1-x86_64.pl
@@ -92,10 +92,24 @@
 ( $xlate="${dir}../../perlasm/x86_64-xlate.pl" and -f $xlate) or
 die "can't locate x86_64-xlate.pl";
 
-# 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.
-$avx = 2;
+if (`$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);
+}
 
 # 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 c08adaa..80867d2 100644
--- a/crypto/sha/asm/sha256-586.pl
+++ b/crypto/sha/asm/sha256-586.pl
@@ -68,10 +68,24 @@
 $xmm=$avx=0;
 for (@ARGV) { $xmm=1 if (/-DOPENSSL_IA32_SSE2/); }
 
-# 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.
-$avx = 2 if ($xmm);
+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) + ($1>=2.22);
+}
+
+if ($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);
+}
 
 $shaext=$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 4082e6b..a7da786 100644
--- a/crypto/sha/asm/sha512-x86_64.pl
+++ b/crypto/sha/asm/sha512-x86_64.pl
@@ -109,10 +109,24 @@
 ( $xlate="${dir}../../perlasm/x86_64-xlate.pl" and -f $xlate) or
 die "can't locate x86_64-xlate.pl";
 
-# 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.
-$avx = 2;
+if (`$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);
+}
 
 # TODO(davidben): Consider enabling the Intel SHA Extensions code once it's
 # been tested.