kernel: fix initramfs reproducibility

Make sure xz uses at least 2 threads so compression always runs in
multi-threaded mode as the resulting file in single-threaded mode
differs.

Fixes: 29d7461d11 ("kernel: set options to make external initramfs reproducible")
Signed-off-by: Daniel Golle <daniel@makrotopia.org>

diff --git a/include/kernel-defaults.mk b/include/kernel-defaults.mk
index af1d59c481041dd25cdf745a2501287670593339..1e82f7d73994926a36d9b82912e6724594f022a7 100644 (file)
--- a/include/kernel-defaults.mk
+++ b/include/kernel-defaults.mk
@@ -181,7 +181,7 @@ endif
        $(if $(CONFIG_TARGET_INITRAMFS_COMPRESSION_GZIP),gzip -n -f -S .gzip -9n $(KERNEL_BUILD_DIR)/initrd.cpio)
        $(if $(CONFIG_TARGET_INITRAMFS_COMPRESSION_LZMA),$(STAGING_DIR_HOST)/bin/lzma e -lc1 -lp2 -pb2 $(KERNEL_BUILD_DIR)/initrd.cpio $(KERNEL_BUILD_DIR)/initrd.cpio.lzma)
 # ?    $(if $(CONFIG_TARGET_INITRAMFS_COMPRESSION_LZO),)
-       $(if $(CONFIG_TARGET_INITRAMFS_COMPRESSION_XZ),$(STAGING_DIR_HOST)/bin/xz -T0 -9 -fz --check=crc32 $(KERNEL_BUILD_DIR)/initrd.cpio)
+       $(if $(CONFIG_TARGET_INITRAMFS_COMPRESSION_XZ),$(STAGING_DIR_HOST)/bin/xz -T$(if $(filter 1,$(NPROC)),2,0) -9 -fz --check=crc32 $(KERNEL_BUILD_DIR)/initrd.cpio)
 # ?    $(if $(CONFIG_TARGET_INITRAMFS_COMPRESSION_LZ4),)
        $(if $(CONFIG_TARGET_INITRAMFS_COMPRESSION_ZSTD),$(STAGING_DIR_HOST)/bin/zstd -T0 -f -o $(KERNEL_BUILD_DIR)/initrd.cpio.zstd $(KERNEL_BUILD_DIR)/initrd.cpio)
 endif