Merge branch 'bpftool: Add LLVM as default library for disassembling JIT-ed programs'

Quentin Monnet says:

====================

To disassemble instructions for JIT-ed programs, bpftool has relied on the
libbfd library. This has been problematic in the past: libbfd's interface
is not meant to be stable and has changed several times, hence the
detection of the two related features from the Makefile
(disassembler-four-args and disassembler-init-styled). When it comes to
shipping bpftool, this has also caused issues with several distribution
maintainers unwilling to support the feature (for example, Debian's page
for binutils-dev, libbfd's package, says: "Note that building Debian
packages which depend on the shared libbfd is Not Allowed.").

This patchset adds support for LLVM as the primary library for
disassembling instructions for JIT-ed programs.

We keep libbfd as a fallback. One reason for this is that currently it
works well, we have all we need in terms of features detection in the
Makefile, so it provides a fallback for disassembling JIT-ed programs if
libbfd is installed but LLVM is not. The other reason is that libbfd
supports nfp instruction for Netronome's SmartNICs and can be used to
disassemble offloaded programs, something that LLVM cannot do (Niklas
confirmed that the feature is still in use). However, if libbfd's interface
breaks again in the future, we might reconsider keeping support for it.

v4:
  - Rebase to address a conflict with commit 2c76238 ("bpftool: Add
    "bootstrap" feature to version output").

v3:
  - Extend commit description (patch 6) with notes on llvm-dev and LLVM's
    disassembler stability.

v2:
  - Pass callback when creating the LLVM disassembler, so that the
    branch targets are printed as addresses (instead of byte offsets).
  - Add last commit to "support" other arch with LLVM, although we don't
    know any supported triple yet.
  - Use $(LLVM_CONFIG) instead of llvm-config in Makefile.
  - Pass components to llvm-config --libs to limit the number of
    libraries to pass on the command line, in Makefile.
  - Rebase split of FEATURE_TESTS and FEATURE_DISPLAY in Makefile.
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: Alexei Starovoitov

tools/bpf/bpftool/Documentation/common_options.rst

@@ -7,10 +7,10 @@
 	  Print bpftool's version number (similar to **bpftool version**), the
 	  number of the libbpf version in use, and optional features that were
 	  included when bpftool was compiled. Optional features include linking
-	  against libbfd to provide the disassembler for JIT-ted programs
-	  (**bpftool prog dump jited**) and usage of BPF skeletons (some
-	  features like **bpftool prog profile** or showing pids associated to
-	  BPF objects may rely on it).
+	  against LLVM or libbfd to provide the disassembler for JIT-ted
+	  programs (**bpftool prog dump jited**) and usage of BPF skeletons
+	  (some features like **bpftool prog profile** or showing pids
+	  associated to BPF objects may rely on it).
 
 -j, --json
 	  Generate JSON output. For commands that cannot produce JSON, this

tools/bpf/bpftool/Makefile

@@ -93,11 +93,22 @@ INSTALL ?= install
 RM ?= rm -f
 
 FEATURE_USER = .bpftool
-FEATURE_TESTS = libbfd libbfd-liberty libbfd-liberty-z \
-	disassembler-four-args disassembler-init-styled libcap \
-	clang-bpf-co-re
-FEATURE_DISPLAY = libbfd libbfd-liberty libbfd-liberty-z \
-	libcap clang-bpf-co-re
+
+FEATURE_TESTS := clang-bpf-co-re
+FEATURE_TESTS += llvm
+FEATURE_TESTS += libcap
+FEATURE_TESTS += libbfd
+FEATURE_TESTS += libbfd-liberty
+FEATURE_TESTS += libbfd-liberty-z
+FEATURE_TESTS += disassembler-four-args
+FEATURE_TESTS += disassembler-init-styled
+
+FEATURE_DISPLAY := clang-bpf-co-re
+FEATURE_DISPLAY += llvm
+FEATURE_DISPLAY += libcap
+FEATURE_DISPLAY += libbfd
+FEATURE_DISPLAY += libbfd-liberty
+FEATURE_DISPLAY += libbfd-liberty-z
 
 check_feat := 1
 NON_CHECK_FEAT_TARGETS := clean uninstall doc doc-clean doc-install doc-uninstall
@@ -115,13 +126,6 @@ include $(FEATURES_DUMP)
 endif
 endif
 
-ifeq ($(feature-disassembler-four-args), 1)
-CFLAGS += -DDISASM_FOUR_ARGS_SIGNATURE
-endif
-ifeq ($(feature-disassembler-init-styled), 1)
-    CFLAGS += -DDISASM_INIT_STYLED
-endif
-
 LIBS = $(LIBBPF) -lelf -lz
 LIBS_BOOTSTRAP = $(LIBBPF_BOOTSTRAP) -lelf -lz
 ifeq ($(feature-libcap), 1)
@@ -133,21 +137,41 @@ include $(wildcard $(OUTPUT)*.d)
 
 all: $(OUTPUT)bpftool
 
-BFD_SRCS = jit_disasm.c
+SRCS := $(wildcard *.c)
 
-SRCS = $(filter-out $(BFD_SRCS),$(wildcard *.c))
-
-ifeq ($(feature-libbfd),1)
-  LIBS += -lbfd -ldl -lopcodes
-else ifeq ($(feature-libbfd-liberty),1)
-  LIBS += -lbfd -ldl -lopcodes -liberty
-else ifeq ($(feature-libbfd-liberty-z),1)
-  LIBS += -lbfd -ldl -lopcodes -liberty -lz
+ifeq ($(feature-llvm),1)
+  # If LLVM is available, use it for JIT disassembly
+  CFLAGS  += -DHAVE_LLVM_SUPPORT
+  LLVM_CONFIG_LIB_COMPONENTS := mcdisassembler all-targets
+  CFLAGS  += $(shell $(LLVM_CONFIG) --cflags --libs $(LLVM_CONFIG_LIB_COMPONENTS))
+  LIBS    += $(shell $(LLVM_CONFIG) --libs $(LLVM_CONFIG_LIB_COMPONENTS))
+  LDFLAGS += $(shell $(LLVM_CONFIG) --ldflags)
+else
+  # Fall back on libbfd
+  ifeq ($(feature-libbfd),1)
+    LIBS += -lbfd -ldl -lopcodes
+  else ifeq ($(feature-libbfd-liberty),1)
+    LIBS += -lbfd -ldl -lopcodes -liberty
+  else ifeq ($(feature-libbfd-liberty-z),1)
+    LIBS += -lbfd -ldl -lopcodes -liberty -lz
+  endif
+
+  # If one of the above feature combinations is set, we support libbfd
+  ifneq ($(filter -lbfd,$(LIBS)),)
+    CFLAGS += -DHAVE_LIBBFD_SUPPORT
+
+    # Libbfd interface changed over time, figure out what we need
+    ifeq ($(feature-disassembler-four-args), 1)
+      CFLAGS += -DDISASM_FOUR_ARGS_SIGNATURE
+    endif
+    ifeq ($(feature-disassembler-init-styled), 1)
+      CFLAGS += -DDISASM_INIT_STYLED
+    endif
+  endif
 endif
-
-ifneq ($(filter -lbfd,$(LIBS)),)
-CFLAGS += -DHAVE_LIBBFD_SUPPORT
-SRCS += $(BFD_SRCS)
+ifeq ($(filter -DHAVE_LLVM_SUPPORT -DHAVE_LIBBFD_SUPPORT,$(CFLAGS)),)
+  # No support for JIT disassembly
+  SRCS := $(filter-out jit_disasm.c,$(SRCS))
 endif
 
 HOST_CFLAGS = $(subst -I$(LIBBPF_INCLUDE),-I$(LIBBPF_BOOTSTRAP_INCLUDE),\

tools/bpf/bpftool/common.c

@@ -1,7 +1,9 @@
 // SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
 /* Copyright (C) 2017-2018 Netronome Systems, Inc. */
 
+#ifndef _GNU_SOURCE
 #define _GNU_SOURCE
+#endif
 #include <ctype.h>
 #include <errno.h>
 #include <fcntl.h>
@@ -625,12 +627,11 @@ static int read_sysfs_netdev_hex_int(char *devname, const char *entry_name)
 }
 
 const char *
-ifindex_to_bfd_params(__u32 ifindex, __u64 ns_dev, __u64 ns_ino,
-		      const char **opt)
+ifindex_to_arch(__u32 ifindex, __u64 ns_dev, __u64 ns_ino, const char **opt)
 {
+	__maybe_unused int device_id;
 	char devname[IF_NAMESIZE];
 	int vendor_id;
-	int device_id;
 
 	if (!ifindex_to_name_ns(ifindex, ns_dev, ns_ino, devname)) {
 		p_err("Can't get net device name for ifindex %d: %s", ifindex,
@@ -645,6 +646,7 @@ ifindex_to_bfd_params(__u32 ifindex, __u64 ns_dev, __u64 ns_ino,
 	}
 
 	switch (vendor_id) {
+#ifdef HAVE_LIBBFD_SUPPORT
 	case 0x19ee:
 		device_id = read_sysfs_netdev_hex_int(devname, "device");
 		if (device_id != 0x4000 &&
@@ -653,8 +655,10 @@ ifindex_to_bfd_params(__u32 ifindex, __u64 ns_dev, __u64 ns_ino,
 			p_info("Unknown NFP device ID, assuming it is NFP-6xxx arch");
 		*opt = "ctx4";
 		return "NFP-6xxx";
+#endif /* HAVE_LIBBFD_SUPPORT */
+	/* No NFP support in LLVM, we have no valid triple to return. */
 	default:
-		p_err("Can't get bfd arch name for device vendor id 0x%04x",
+		p_err("Can't get arch name for device vendor id 0x%04x",
 		      vendor_id);
 		return NULL;
 	}

tools/bpf/bpftool/iter.c

@@ -1,7 +1,9 @@
 // SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
 // Copyright (C) 2020 Facebook
 
+#ifndef _GNU_SOURCE
 #define _GNU_SOURCE
+#endif
 #include <unistd.h>
 #include <linux/err.h>
 #include <bpf/libbpf.h>