Hi,
Attached is a patch to improve libsanitizer build times by exposing the DAG to
the GNU Make jobserver, in the style of Peter Miller's "Recursive Make
Considered Harmful" from 1997.
Tested on x86_64-linux-gnu.
Thanks,
Harmen Stoppels
From 7742c383cff74dc922ba140bf0850fdf990f8430 Mon Sep 17 00:00:00 2001
From: Harmen Stoppels <[email protected]>
Date: Thu, 18 Jun 2026 13:04:28 +0200
Subject: [PATCH] libsanitizer: parallelize subdir builds
Automake normally builds subdirectories sequentially, which makes the
libsanitizer builds effectively sequential as there is little parallelism per
subdirectory. This patch replaces the all-recursive loop with an explicit
dependency graph: asan and hwasan depend on lsan, while others just need
sanitizer_common.
Exposing this DAG to make raises the CPU load from 2.3 to 3.7, yielding a
roughly 30% reduction in build time on multi-core machines.
libsanitizer/ChangeLog:
* Makefile.am: Override all-recursive and define explicit
DAG dependencies for all-* targets to enable parallel builds.
* Makefile.in: Regenerate.
---
libsanitizer/Makefile.am | 24 ++++++++++++++++++++++++
libsanitizer/Makefile.in | 20 ++++++++++++++++++++
2 files changed, 44 insertions(+)
diff --git a/libsanitizer/Makefile.am b/libsanitizer/Makefile.am
index 53e20bdac2c..2e3245c8d87 100644
--- a/libsanitizer/Makefile.am
+++ b/libsanitizer/Makefile.am
@@ -26,6 +26,30 @@ endif
if HWASAN_SUPPORTED
SUBDIRS += hwasan
endif
+
+# Override all-recursive and explicitly define the dependency graph
+# to increase parallelism during the build.
+
+all-sanitizer_common all-interception all-libbacktrace:
+ +cd $(@:all-%=%) && $(MAKE) $(AM_MAKEFLAGS) all
+
+SANITIZER_BASE_DEPS = all-sanitizer_common
+if !USING_MAC_INTERPOSE
+SANITIZER_BASE_DEPS += all-interception
+endif
+if LIBBACKTRACE_SUPPORTED
+SANITIZER_BASE_DEPS += all-libbacktrace
+endif
+
+all-lsan all-ubsan all-tsan: $(SANITIZER_BASE_DEPS)
+ +cd $(@:all-%=%) && $(MAKE) $(AM_MAKEFLAGS) all
+
+all-asan all-hwasan: $(SANITIZER_BASE_DEPS) all-lsan
+ +cd $(@:all-%=%) && $(MAKE) $(AM_MAKEFLAGS) all
+
+all-recursive: $(SUBDIRS:%=all-%)
+
+.PHONY: $(SUBDIRS:%=all-%)
endif
## Force DIST_SUBDIRS so that make distclean works
diff --git a/libsanitizer/Makefile.in b/libsanitizer/Makefile.in
index fa6fe9e26a3..280e45cdbe4 100644
--- a/libsanitizer/Makefile.in
+++ b/libsanitizer/Makefile.in
@@ -98,6 +98,8 @@ target_triplet = @target@
@LIBBACKTRACE_SUPPORTED_TRUE@@SANITIZER_SUPPORTED_TRUE@am__append_3 = libbacktrace
@SANITIZER_SUPPORTED_TRUE@@TSAN_SUPPORTED_TRUE@am__append_4 = tsan
@HWASAN_SUPPORTED_TRUE@@SANITIZER_SUPPORTED_TRUE@am__append_5 = hwasan
+@SANITIZER_SUPPORTED_TRUE@@USING_MAC_INTERPOSE_FALSE@am__append_6 = all-interception
+@LIBBACKTRACE_SUPPORTED_TRUE@@SANITIZER_SUPPORTED_TRUE@am__append_7 = all-libbacktrace
subdir = .
ACLOCAL_M4 = $(top_srcdir)/aclocal.m4
am__aclocal_m4_deps = $(top_srcdir)/../config/acx.m4 \
@@ -370,6 +372,8 @@ nodist_saninclude_HEADERS = $(am__append_1)
@SANITIZER_SUPPORTED_TRUE@SUBDIRS = sanitizer_common $(am__append_2) \
@SANITIZER_SUPPORTED_TRUE@ $(am__append_3) lsan asan ubsan \
@SANITIZER_SUPPORTED_TRUE@ $(am__append_4) $(am__append_5)
+@SANITIZER_SUPPORTED_TRUE@SANITIZER_BASE_DEPS = all-sanitizer_common \
+@SANITIZER_SUPPORTED_TRUE@ $(am__append_6) $(am__append_7)
DIST_SUBDIRS = $(SUBDIRS)
gcc_version := $(shell @get_gcc_base_ver@ $(top_srcdir)/../gcc/BASE-VER)
@@ -765,6 +769,22 @@ uninstall-am: uninstall-nodist_sanincludeHEADERS \
.PRECIOUS: Makefile
+# Override all-recursive and explicitly define the dependency graph
+# to increase parallelism during the build.
+
+@SANITIZER_SUPPORTED_TRUE@all-sanitizer_common all-interception all-libbacktrace:
+@SANITIZER_SUPPORTED_TRUE@ +cd $(@:all-%=%) && $(MAKE) $(AM_MAKEFLAGS) all
+
+@SANITIZER_SUPPORTED_TRUE@all-lsan all-ubsan all-tsan: $(SANITIZER_BASE_DEPS)
+@SANITIZER_SUPPORTED_TRUE@ +cd $(@:all-%=%) && $(MAKE) $(AM_MAKEFLAGS) all
+
+@SANITIZER_SUPPORTED_TRUE@all-asan all-hwasan: $(SANITIZER_BASE_DEPS) all-lsan
+@SANITIZER_SUPPORTED_TRUE@ +cd $(@:all-%=%) && $(MAKE) $(AM_MAKEFLAGS) all
+
+@SANITIZER_SUPPORTED_TRUE@all-recursive: $(SUBDIRS:%=all-%)
+
+@[email protected]: $(SUBDIRS:%=all-%)
+
# GNU Make needs to see an explicit $(MAKE) variable in the command it
# runs to enable its job server during parallel builds. Hence the
# comments below.
--
2.43.0
