Introduce a HOMEBREW_ARCH environment variable to specify target microarchitecture

[sjackman]

From @eiennohito on April 22, 2016 5:16

It is useful in scenarios when you have heterogenous grid of computers with different microarchitectures and want to build binaries that can be used everywhere.

Discussion is started in #1094.

Copied from original issue: Linuxbrew/legacy-linuxbrew#1095

[sjackman]

From @eiennohito on May 16, 2016 4:13

-march=native started to make shared installation unusable in our environment :(

[sjackman]

Sorry for the breakage, Arseny. Try the following workaround:

diff --git a/Library/Homebrew/extend/ENV/std.rb b/Library/Homebrew/extend/ENV/std.rb
index 3d1b2a8..df84dcf 100644
--- a/Library/Homebrew/extend/ENV/std.rb
+++ b/Library/Homebrew/extend/ENV/std.rb
@@ -8,7 +8,7 @@ module Stdenv

   # @private
   SAFE_CFLAGS_FLAGS = "-w -pipe"
-  DEFAULT_FLAGS = OS.mac? ? "-march=core2 -msse4" : "-march=native"
+  DEFAULT_FLAGS = "-march=core2 -msse4"

   def self.extended(base)
     unless ORIGINAL_PATHS.include? HOMEBREW_PREFIX/"bin"

[sjackman]

I've added the requested HOMEBREW_ARCH environment variable. Just for my curiosity, what value are you planning to use? Linuxbrew bottles use -march=core2, so I'd suggest HOMEBREW_ARCH=core2 if that works for you.

[eiennohito]

Thank you very much, this is great.

As a workaround I have temporarily made the brew upgrade job to execute on the oldest machine, but this should fix it.

Regarding the value, it will be either core2 or nehalem, I need to do a better hardware survey before deciding that.

[staticfloat]

Thanks for this Shaun.

To anyone frustrated with trying to compile software using linuxbrew on a Raspberry Pi, note that because Linuxbrew sends -mcpu=native to GCC, and GCC 4.9.2 suffers from this bug in the current version of Raspbian, no software can be installed using Linuxbrew without setting HOMEBREW_ARCH to something other than native. In the case of the Raspberry Pi 3, I have found HOMEBREW_ARCH=armv8-a+crc to work well.

[sjackman]

Thanks for the heads up, Elliot. How frustrating!