From dc40c49df43c2540882647336414232a44834803 Mon Sep 17 00:00:00 2001
From: Kevin Krakauer <krakauer@google.com>
Date: Fri, 15 Dec 2023 16:11:31 -0800
Subject: [PATCH] images: use mulitarch default image instead of hacky
 workaround

Instead of lying to clang about the targeted system, we can install the
necessary package only on x86_64 machines. Our tooling supports multiarch
packages (see tools/images.mk).

PiperOrigin-RevId: 591385576
---
 images/default/Dockerfile |  4 ++++
 tools/bazeldefs/defs.bzl  | 18 +-----------------
 2 files changed, 5 insertions(+), 17 deletions(-)

diff --git a/images/default/Dockerfile b/images/default/Dockerfile
index 683028ce1..cd66962dc 100644
--- a/images/default/Dockerfile
+++ b/images/default/Dockerfile
@@ -10,6 +10,10 @@ RUN apt-get update && apt-get install -y curl gnupg2 git \
         pkg-config libffi-dev patch diffutils libssl-dev iptables kmod \
         clang crossbuild-essential-amd64 erofs-utils busybox-static libbpf-dev
 
+# This package is needed to build eBPF on amd64, but not on arm64 where it
+# doesn't exist.
+RUN test "$(uname -m)" != x86_64 && exit 0 || apt-get install -y libc6-dev-i386
+
 # Install Docker client for the website build.
 RUN curl -fsSL https://download.docker.com/linux/ubuntu/gpg | apt-key add -
 RUN add-apt-repository \
diff --git a/tools/bazeldefs/defs.bzl b/tools/bazeldefs/defs.bzl
index 0d7114c50..f986029b9 100644
--- a/tools/bazeldefs/defs.bzl
+++ b/tools/bazeldefs/defs.bzl
@@ -104,21 +104,5 @@ def bpf_program(name, src, bpf_object, visibility, hdrs):
         srcs = [src],
         visibility = visibility,
         outs = [bpf_object],
-        # Note: "-D __x86_64__" is a hack to deal with building across
-        # architectures. As we're targeting eBPF, setting this doesn't lead to
-        # any x86_64-specific code. But it does help with an annoying edge
-        # case:
-        #
-        # We have a single container -- images/default -- that runs on both
-        # arm64 and x86_64 machines. To build eBPF on x86_64, package
-        # gcc-multilib or libc6-dev-i386 is needed to install headers. But
-        # these don't exist on arm64, so adding it to the image breaks arm64
-        # builds.
-        #
-        # Defining __x86_64__ lets us avoid the need for these packages
-        # altogether. It turns out that the missing headers are irrelevant
-        # (unused) when building eBPF, and pretending we're targeting x86_64
-        # causes #includes to resolve without installing architecture-specific
-        # packages.
-        cmd = "clang -O2 -Wall -Werror -target bpf -c $< -o $@ -I/usr/include/$$(uname -m)-linux-gnu -D __x86_64__",
+        cmd = "clang -O2 -Wall -Werror -target bpf -c $< -o $@ -I/usr/include/$$(uname -m)-linux-gnu",
     )