From c6c024ca6f587dab991589ad6fdf010b9f0e6d62 Mon Sep 17 00:00:00 2001
From: Gergely Risko <gergely@risko.hu>
Date: Thu, 22 Aug 2013 17:57:39 +0200
Subject: [PATCH] Fix personality switching from x86_64 to i686

On Linux, Nix can build i686 packages even on x86_64 systems.  It's not
enough to recognize this situation by settings.thisSystem, we also have
to consult uname().  E.g. we can be running on a i686 Debian with an
amd64 kernel.  In that situation settings.thisSystem is i686-linux, but
we still need to change personality to i686 to make builds consistent.
---
 src/libstore/build.cc | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index 67e38da0b..b5d064e8c 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -21,6 +21,7 @@
 #include <sys/wait.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <sys/utsname.h>
 #include <fcntl.h>
 #include <unistd.h>
 #include <errno.h>
@@ -2173,7 +2174,11 @@ void DerivationGoal::initChild()
 #ifdef CAN_DO_LINUX32_BUILDS
         /* Change the personality to 32-bit if we're doing an
            i686-linux build on an x86_64-linux machine. */
-        if (drv.platform == "i686-linux" && settings.thisSystem == "x86_64-linux") {
+        struct utsname utsbuf;
+        uname(&utsbuf);
+        if (drv.platform == "i686-linux" &&
+            (settings.thisSystem == "x86_64-linux" ||
+             (!strcmp(utsbuf.sysname, "Linux") && !strcmp(utsbuf.machine, "x86_64")))) {
             if (personality(0x0008 | 0x8000000 /* == PER_LINUX32_3GB */) == -1)
                 throw SysError("cannot set i686-linux personality");
         }