Add --disable-asm option to disable assembly implementations.

Check that fesetenv() and fegetenv() are available. If they aren't, still
compile the floating-point implementation of poly1305, but never pick it
in sodium_init().

This helps libsodium compile and work on Emscripten and on environments with
an incomplete libc.

configure.ac

@@ -179,6 +179,20 @@ AC_CHECK_HEADERS([wmmintrin.h], [], [], [
 #pragma GCC target("aes")
 ])
 
+AC_MSG_CHECKING(for access to floating-point rounding mode)
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
+  #include <fenv.h>
+  #pragma STDC FENV_ACCESS ON
+]], [[
+  const int previous_rounding_mode = fegetround();
+  fesetround(FE_TONEAREST);
+  fesetround(previous_rounding_mode);
+]])],
+[AC_MSG_RESULT(yes)
+ AC_DEFINE([HAVE_FENV_H], [1], [floating-point rounding mode is accessible])
+],
+[AC_MSG_RESULT(no)])
+
 dnl Checks for typedefs, structures, and compiler characteristics.
 
 AC_C_BIGENDIAN(
@@ -201,10 +215,11 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
    CPPFLAGS="$CPPFLAGS -D__STDC_LIMIT_MACROS -D__STDC_CONSTANT_MACROS"
 ])
 
-AC_MSG_CHECKING(whether we can assemble basic amd64 code)
 HAVE_AMD64_ASM_V=0
-AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
+AS_IF([test "$enable_asm" != "no"],[
-]], [[
+  AC_MSG_CHECKING(whether we can assemble basic amd64 code)
+  AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
+  ]], [[
 #if defined(__amd64) || defined(__amd64__) || defined(__x86_64__)
 /* neat */
 #else
@@ -212,10 +227,11 @@ AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
 #endif
 __asm__("pxor %xmm12,%xmm6");
 ]])],
-[AC_MSG_RESULT(yes)
+  [AC_MSG_RESULT(yes)
    AC_DEFINE([HAVE_AMD64_ASM], [1], [basic amd64 code can be assembled])
    HAVE_AMD64_ASM_V=1],
-[AC_MSG_RESULT(no)])
+  [AC_MSG_RESULT(no)])
+])
 AM_CONDITIONAL([HAVE_AMD64_ASM], [test $HAVE_AMD64_ASM_V = 1])
 AC_SUBST(HAVE_AMD64_ASM_V)
 
@@ -267,6 +283,19 @@ AC_ARG_ENABLE(pie,
 [AS_HELP_STRING(--enable-pie,Produce position independent executables @<:@default=yes@:>@)],
  enable_pie=$enableval, enable_pie="maybe")
 
+AC_ARG_ENABLE(asm,
+[AS_HELP_STRING(--disable-asm,Disable assembly implementations)],
+[
+  AS_IF([test "x$enableval" = "xno"], [
+    enable_asm="no"
+  ], [
+    enable_asm="yes"
+  ])
+],
+[
+  enable_asm="yes"
+])
+
 AC_ARG_ENABLE(ssp,
 [AS_HELP_STRING(--disable-ssp,Don't compile with -fstack-protector)],
 [AS_IF([test "x$enableval" = "xno"], [

src/libsodium/crypto_onetimeauth/poly1305/53/auth_poly1305_53.c

@@ -4,7 +4,9 @@ D. J. Bernstein
 Public domain.
 */
 
-#include <fenv.h>
+#ifdef HAVE_FENV_H
+# include <fenv.h>
+#endif
 #include <stdint.h>
 #include <stdlib.h>
 
@@ -12,7 +14,9 @@ Public domain.
 #include "crypto_onetimeauth_poly1305_53.h"
 #include "utils.h"
 
-#pragma STDC FENV_ACCESS ON
+#ifdef HAVE_FENV_H
+# pragma STDC FENV_ACCESS ON
+#endif
 
 typedef uint8_t  uchar;
 typedef int32_t  int32;
@@ -238,12 +242,14 @@ int crypto_onetimeauth(unsigned char *out,const unsigned char *m,unsigned long l
   register uint64 g3;
   register uint64 g4;
 
+#ifdef HAVE_FENV_H
   const int previous_rounding_mode = fegetround();
   if (previous_rounding_mode != FE_TONEAREST) {
       if (fesetround(FE_TONEAREST) != 0) {
           return -1;
       }
   }
+#endif
 
   r00 = *(uchar *) (r + 0);
   constants = (char *) &poly1305_53_constants;
@@ -1627,10 +1633,13 @@ nomorebytes:;
   f3 >>= 8;
   *(uchar *) (out + 15) = f3;
 
+#ifdef HAVE_FENV_H
   if (previous_rounding_mode != FE_TONEAREST &&
       fesetround(previous_rounding_mode) != 0) {
       abort();
   }
+#endif
+
   return 0;
 }
 

src/libsodium/crypto_onetimeauth/poly1305/onetimeauth_poly1305_try.c

@@ -123,7 +123,9 @@ crypto_onetimeauth_poly1305_implementation *
 crypto_onetimeauth_pick_best_implementation(void)
 {
     crypto_onetimeauth_poly1305_implementation *implementations[] = {
+#ifdef HAVE_FENV_H
         &crypto_onetimeauth_poly1305_53_implementation,
+#endif
         &crypto_onetimeauth_poly1305_ref_implementation,
         NULL
     };