From 77038ab61a23ac53dc8d3b3a08abb576d9971503 Mon Sep 17 00:00:00 2001
From: Brad Smith <brad@comstyle.com>
Date: Thu, 5 Nov 2026 12:14:07 -0500
Subject: [PATCH] build: only build huf_decompress_amd64.S on x86_64

The Make and Meson builds add the x86_64 Huffman decoder assembly
source to every build, whatever the target CPU. Match the CMake build
and only build it when targeting x86_64, otherwise explicitly disable
assembly.

For Make, ask the compiler whether it targets x86_64, rather than
using uname, so cross-compiling and -m32 builds are handled. For
Meson, check the host machine's CPU family.
---
 build/meson/lib/meson.build |  3 ++-
 lib/libzstd.mk              | 12 ++++++------
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/build/meson/lib/meson.build b/build/meson/lib/meson.build
index 81fc313f954..ae16d655426 100644
--- a/build/meson/lib/meson.build
+++ b/build/meson/lib/meson.build
@@ -46,10 +46,11 @@ libzstd_sources = [join_paths(zstd_rootdir, 'lib/common/entropy_common.c'),
   join_paths(zstd_rootdir, 'lib/dictBuilder/divsufsort.c'),
   join_paths(zstd_rootdir, 'lib/dictBuilder/zdict.c')]
 
+# The assembly source only has an x86_64 implementation, so only build it there.
 # really we need anything that defines __GNUC__ as that is what ZSTD_ASM_SUPPORTED is gated on
 # but these are the two compilers that are supported in tree and actually handle this correctly
 # Otherwise, explicitly disable assembly.
-if [compiler_gcc, compiler_clang].contains(cc_id)
+if host_machine.cpu_family() == 'x86_64' and [compiler_gcc, compiler_clang].contains(cc_id)
   libzstd_sources += join_paths(zstd_rootdir, 'lib/decompress/huf_decompress_amd64.S')
 else
   add_project_arguments('-DZSTD_DISABLE_ASM', language: 'c')
diff --git a/lib/libzstd.mk b/lib/libzstd.mk
index 60928b0ee95..9055da61fed 100644
--- a/lib/libzstd.mk
+++ b/lib/libzstd.mk
@@ -49,9 +49,6 @@ else
   ZSTD_STRIP_ERROR_STRINGS ?= 0
 endif
 
-# Assembly support
-ZSTD_NO_ASM ?= 0
-
 ZSTD_LIB_EXCLUDE_COMPRESSORS_DFAST_AND_UP ?= 0
 ZSTD_LIB_EXCLUDE_COMPRESSORS_GREEDY_AND_UP ?= 0
 
@@ -151,11 +148,14 @@ ZSTD_LEGACY_FILES :=
 
 ZSTD_DECOMPRESS_AMD64_ASM_FILES := $(sort $(wildcard $(LIB_SRCDIR)/decompress/*_amd64.S))
 
-ifneq ($(ZSTD_NO_ASM), 0)
+# The assembly sources only have an x86_64 implementation, so only build
+# them when the compiler targets x86_64. Ask the compiler instead of using
+# uname so that cross-compiling and -m32 builds do the right thing.
+ZSTD_ASM_X86_64 := $(shell echo | $(CC) $(CPPFLAGS) $(CFLAGS) -dM -E - 2>$(VOID) | $(GREP) -c '__x86_64__')
+
+ifeq ($(ZSTD_ASM_X86_64), 0)
   CPPFLAGS += -DZSTD_DISABLE_ASM
 else
-  # Unconditionally add the ASM files they are disabled by
-  # macros in the .S file.
   ZSTD_DECOMPRESS_FILES += $(ZSTD_DECOMPRESS_AMD64_ASM_FILES)
 endif