[RFC PATCH v2 3/3] bpftool: Prefer zlib-rs over zlib when available

[Ian Rogers <irogers@google.com>]

Add zlib-rs and zlib to FEATURE_TESTS and FEATURE_DISPLAY in
tools/bpf/bpftool/Makefile and use feature_rust_lib to configure
ZLIB_CFLAGS and ZLIB_LIBS when zlib-rs is detected (unless disabled with
NO_ZLIB_RS=1), falling back to -lz.

Decompression of kernel configuration (/proc/config.gz) and compressed
ELF/BTF sections (via libbpf, libelf, and libbfd) processes data that
benefits from a memory-safe implementation. Preferring zlib-rs over C
zlib provides memory safety and improved decompression performance while
keeping bpftool aligned with tools/perf (including sharing libz_rs.a
when building bootstrap bpftool for perf BPF skeletons).

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/bpf/bpftool/.gitignore |  1 +
 tools/bpf/bpftool/Makefile   | 57 ++++++++++++++++++++++++++++++++----
 2 files changed, 52 insertions(+), 6 deletions(-)

diff --git a/tools/bpf/bpftool/.gitignore b/tools/bpf/bpftool/.gitignore
index a736f64dc5dc..ea2222373634 100644
--- a/tools/bpf/bpftool/.gitignore
+++ b/tools/bpf/bpftool/.gitignore
@@ -6,5 +6,6 @@ bpftool*.8
 FEATURE-DUMP.bpftool
 feature
 libbpf
+libz_rs
 /*.skel.h
 /vmlinux.h
diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
index b0f7168e7943..16b9a00963e3 100644
--- a/tools/bpf/bpftool/Makefile
+++ b/tools/bpf/bpftool/Makefile
@@ -16,6 +16,8 @@ else
 endif
 BOOTSTRAP_OUTPUT := $(_OUTPUT)bootstrap/
 
+LIBZ_RS_OUTPUT := $(_OUTPUT)libz_rs/
+
 LIBBPF_OUTPUT := $(_OUTPUT)libbpf/
 LIBBPF_DESTDIR := $(LIBBPF_OUTPUT)
 LIBBPF_INCLUDE := $(LIBBPF_DESTDIR)include
@@ -38,7 +40,9 @@ $(LIBBPF_OUTPUT) $(BOOTSTRAP_OUTPUT) $(LIBBPF_BOOTSTRAP_OUTPUT) $(LIBBPF_HDRS_DI
 
 $(LIBBPF): $(wildcard $(BPF_DIR)/*.[ch] $(BPF_DIR)/Makefile) | $(LIBBPF_OUTPUT)
 	$(Q)$(MAKE) -C $(BPF_DIR) OUTPUT=$(LIBBPF_OUTPUT) \
-		DESTDIR=$(LIBBPF_DESTDIR:/=) prefix= $(LIBBPF) install_headers
+		DESTDIR=$(LIBBPF_DESTDIR:/=) prefix= \
+		$(if $(ZLIB_CFLAGS),EXTRA_CFLAGS="$(or $(EXTRA_CFLAGS),-g -O2) $(ZLIB_CFLAGS)") \
+		$(LIBBPF) install_headers
 
 $(LIBBPF_INTERNAL_HDRS): $(LIBBPF_HDRS_DIR)/%.h: $(BPF_DIR)/%.h | $(LIBBPF_HDRS_DIR)
 	$(call QUIET_INSTALL, $@)
@@ -115,8 +119,20 @@ ifneq ($(SKIP_CRYPTO),1)
   CRYPTO_LIBS := -lcrypto
 endif
 
+ifneq ($(CROSS_COMPILE),)
+  ifneq ($(MAKECMDGOALS),bootstrap)
+    ifneq ($(RUST_TARGET_FLAGS_$(ARCH)),)
+      RUST_FLAGS += --target=$(RUST_TARGET_FLAGS_$(ARCH))
+    else
+      NO_ZLIB_RS := 1
+    endif
+  else
+    NO_ZLIB_RS := 1
+  endif
+endif
+
 ifeq ($(MAKECMDGOALS),bootstrap)
-FEATURE_TESTS := libelf-zstd
+FEATURE_TESTS := libelf-zstd $(if $(NO_ZLIB_RS),,zlib-rs) zlib
 FEATURE_DISPLAY :=
 else
 FEATURE_TESTS := clang-bpf-co-re
@@ -128,6 +144,10 @@ FEATURE_TESTS += libbfd-liberty-z
 FEATURE_TESTS += disassembler-four-args
 FEATURE_TESTS += disassembler-init-styled
 FEATURE_TESTS += libelf-zstd
+ifeq ($(NO_ZLIB_RS),)
+FEATURE_TESTS += zlib-rs
+endif
+FEATURE_TESTS += zlib
 
 FEATURE_DISPLAY := clang-bpf-co-re
 FEATURE_DISPLAY += llvm
@@ -135,6 +155,10 @@ FEATURE_DISPLAY += libcap
 FEATURE_DISPLAY += libbfd
 FEATURE_DISPLAY += libbfd-liberty
 FEATURE_DISPLAY += libbfd-liberty-z
+ifeq ($(NO_ZLIB_RS),)
+FEATURE_DISPLAY += zlib-rs
+endif
+FEATURE_DISPLAY += zlib
 endif
 
 check_feat := 1
@@ -153,8 +177,29 @@ include $(FEATURES_DUMP)
 endif
 endif
 
-LIBS = $(LIBBPF) -lelf $(CRYPTO_LIBS) -lz
-LIBS_BOOTSTRAP = $(LIBBPF_BOOTSTRAP) -lelf $(CRYPTO_LIBS) -lz
+# Prefer zlib-rs over C zlib when detected (libz_rs.a exports the full zlib C
+# ABI including both gzopen and gzopen64, so it is also compatible with a
+# pre-built libbpf.a compiled against system <zlib.h> with _FILE_OFFSET_BITS=64).
+# When cross-compiling, the host bootstrap bpftool still links against the
+# host's -lz.
+ZLIB_LIBS := -lz
+ZLIB_BOOTSTRAP_LIBS := -lz
+ifeq ($(feature-zlib-rs),1)
+  ifeq ($(NO_ZLIB_RS),)
+    $(call feature_rust_lib,zlib-rs)
+    ZLIB_CFLAGS := $(FEATURE_CFLAGS-zlib-rs)
+    ZLIB_LIBS := $(FEATURE_LIBS-zlib-rs)
+    CFLAGS += $(ZLIB_CFLAGS)
+    ifeq ($(CROSS_COMPILE),)
+      HOST_CFLAGS += $(ZLIB_CFLAGS)
+      LIBBPF_BOOTSTRAP_CFLAGS += $(ZLIB_CFLAGS)
+      ZLIB_BOOTSTRAP_LIBS := $(ZLIB_LIBS)
+    endif
+  endif
+endif
+
+LIBS = $(LIBBPF) -lelf $(CRYPTO_LIBS) $(ZLIB_LIBS)
+LIBS_BOOTSTRAP = $(LIBBPF_BOOTSTRAP) -lelf $(CRYPTO_LIBS) $(ZLIB_BOOTSTRAP_LIBS)
 
 ifeq ($(feature-libelf-zstd),1)
 LIBS += -lzstd
@@ -200,7 +245,7 @@ else
   else ifeq ($(feature-libbfd-liberty),1)
     LIBS += -lbfd -ldl -lopcodes -liberty
   else ifeq ($(feature-libbfd-liberty-z),1)
-    LIBS += -lbfd -ldl -lopcodes -liberty -lz
+    LIBS += -lbfd -ldl -lopcodes -liberty $(ZLIB_LIBS)
   endif
 
   # If one of the above feature combinations is set, we support libbfd
@@ -304,7 +349,7 @@ clean: $(LIBBPF)-clean $(LIBBPF_BOOTSTRAP)-clean feature-detect-clean
 	$(call QUIET_CLEAN, bpftool)
 	$(Q)$(RM) -- $(OUTPUT)bpftool $(OUTPUT)*.o $(OUTPUT)*.d
 	$(Q)$(RM) -- $(OUTPUT)*.skel.h $(OUTPUT)vmlinux.h
-	$(Q)$(RM) -r -- $(LIBBPF_OUTPUT) $(BOOTSTRAP_OUTPUT)
+	$(Q)$(RM) -r -- $(LIBBPF_OUTPUT) $(BOOTSTRAP_OUTPUT) $(LIBZ_RS_OUTPUT)
 	$(call QUIET_CLEAN, core-gen)
 	$(Q)$(RM) -- $(OUTPUT)FEATURE-DUMP.bpftool
 	$(Q)$(RM) -r -- $(OUTPUT)feature/
-- 
2.56.0.317.g454f8302e1-goog