* [PATCH bpf-next v2 0/2] bpftool: Make the LLVM disassembler an optional runtime dependency
@ 2026-10-29 12:43 Mark Korenberg via B4 Relay
2026-10-29 12:43 ` [PATCH bpf-next v2 1/2] bpftool: Fix disposal of the LLVM disassembler context Mark Korenberg via B4 Relay
2026-10-29 12:43 ` [PATCH bpf-next v2 2/2] bpftool: Make the LLVM disassembler an optional runtime dependency Mark Korenberg via B4 Relay
0 siblings, 2 replies; 4+ messages in thread
From: Mark Korenberg via B4 Relay @ 2026-10-29 12:43 UTC (permalink / raw)
To: Quentin Monnet, Alexei Starovoitov, Daniel Borkmann,
Andrii Nakryiko, Martin KaFai Lau, Eduard Zingerman,
Kumar Kartikeya Dwivedi, Song Liu, Yonghong Song, Jiri Olsa,
Nathan Chancellor, Bill Wendling, Justin Stitt, Emil Tsalapatis,
Ihor Solodrai, Nick Desaulniers
Cc: linux-kernel, bpf, llvm, Mark Korenberg
libLLVM (~140 MiB on Fedora) is a hard dependency of bpftool, although it
is only used by "bpftool prog dump jited". This series moves the LLVM
disassembler to a plugin that bpftool loads on demand, so that
distributions can make it optional. Patch 1 fixes a leak found on the way.
Changes in v2:
- Move the LLVMDisasmDispose() fix to a separate patch (Quentin)
- Look for the plugin next to the bpftool binary when it is not installed,
so that bpftool works from its build directory (Quentin, Sashiko). Not in
the current directory: bpftool usually runs as root.
- Export a single versioned structure of callbacks from the plugin (Quentin)
- Only report "llvm" in "bpftool version" if the plugin loads (Quentin)
- Handle dlerror() returning NULL (Quentin)
- Rebuild jit_disasm.o if libdir changes between "make" and
"make install" (Quentin)
- uninstall: use QUIET_UNINST, remove $(libdir)/bpftool (Quentin)
- With a static libLLVM, which a static bpftool requires, link the
disassembler into bpftool as before (Sashiko). This drops
LLVM_LINK_STATIC: static LLVM archives are never linked into a shared
object.
- Commit log and comment fixes (Quentin, Sashiko)
- Rebase on bpf-next
- Link to v1: https://lore.kernel.org/r/20260603-bpftool-plugin-v1-1-68c0ac91f5a3@gmail.com
Tested on Fedora 44 x86_64, LLVM 22: plugin, built-in and SKIP_LLVM
builds; plugin lookup (installed, build directory, missing, wrong ABI);
install/uninstall; "prog dump jited" (plain and JSON) on live programs,
and disassembly of aarch64 code through the plugin. Not tested: a fully
static build (no static libraries available).
The v2 changes were written with the help of an AI assistant (Claude),
from the review comments; I reviewed and tested them.
---
Mark Korenberg (2):
bpftool: Fix disposal of the LLVM disassembler context
bpftool: Make the LLVM disassembler an optional runtime dependency
tools/bpf/bpftool/Makefile | 38 +++++++++-
tools/bpf/bpftool/jit_disasm.c | 161 ++++++++++++++++++++++++++++------------
tools/bpf/bpftool/llvm_disasm.c | 84 +++++++++++++++++++++
tools/bpf/bpftool/llvm_disasm.h | 41 ++++++++++
tools/bpf/bpftool/main.c | 3 +-
tools/bpf/bpftool/main.h | 3 +
6 files changed, 279 insertions(+), 51 deletions(-)
---
base-commit: d80373a8e70d3193151232c3062abbbe367ff5ad
change-id: 20260603-bpftool-plugin-c994bc3e0643
Best regards,
--
Mark Korenberg <socketpair@gmail.com>
^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH bpf-next v2 1/2] bpftool: Fix disposal of the LLVM disassembler context
2026-10-29 12:43 [PATCH bpf-next v2 0/2] bpftool: Make the LLVM disassembler an optional runtime dependency Mark Korenberg via B4 Relay
@ 2026-10-29 12:43 ` Mark Korenberg via B4 Relay
2026-10-29 12:43 ` [PATCH bpf-next v2 2/2] bpftool: Make the LLVM disassembler an optional runtime dependency Mark Korenberg via B4 Relay
1 sibling, 0 replies; 4+ messages in thread
From: Mark Korenberg via B4 Relay @ 2026-10-29 12:43 UTC (permalink / raw)
To: Quentin Monnet, Alexei Starovoitov, Daniel Borkmann,
Andrii Nakryiko, Martin KaFai Lau, Eduard Zingerman,
Kumar Kartikeya Dwivedi, Song Liu, Yonghong Song, Jiri Olsa,
Nathan Chancellor, Bill Wendling, Justin Stitt, Emil Tsalapatis,
Ihor Solodrai, Nick Desaulniers
Cc: linux-kernel, bpf, llvm, Mark Korenberg
From: Mark Korenberg <socketpair@gmail.com>
destroy_context() frees the disassembler context with LLVMDisposeMessage(),
which is a plain free() meant for strings returned by LLVM. The context is
therefore never destroyed, leaking about 28 KiB per disassembled function.
Use LLVMDisasmDispose() instead.
Fixes: eb9d1acf634b ("bpftool: Add LLVM as default library for disassembling JIT-ed programs")
Signed-off-by: Mark Korenberg <socketpair@gmail.com>
---
tools/bpf/bpftool/jit_disasm.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/bpf/bpftool/jit_disasm.c b/tools/bpf/bpftool/jit_disasm.c
index 04541155e9cc..5ff144ce84a1 100644
--- a/tools/bpf/bpftool/jit_disasm.c
+++ b/tools/bpf/bpftool/jit_disasm.c
@@ -115,7 +115,7 @@ init_context(disasm_ctx_t *ctx, const char *arch,
static void destroy_context(disasm_ctx_t *ctx)
{
- LLVMDisposeMessage(*ctx);
+ LLVMDisasmDispose(*ctx);
}
static int
--
2.56.0
^ permalink raw reply related [flat|nested] 4+ messages in thread
* [PATCH bpf-next v2 2/2] bpftool: Make the LLVM disassembler an optional runtime dependency
2026-10-29 12:43 [PATCH bpf-next v2 0/2] bpftool: Make the LLVM disassembler an optional runtime dependency Mark Korenberg via B4 Relay
2026-10-29 12:43 ` [PATCH bpf-next v2 1/2] bpftool: Fix disposal of the LLVM disassembler context Mark Korenberg via B4 Relay
@ 2026-10-29 12:43 ` Mark Korenberg via B4 Relay
2026-10-29 12:54 ` sashiko-bot
1 sibling, 1 reply; 4+ messages in thread
From: Mark Korenberg via B4 Relay @ 2026-10-29 12:43 UTC (permalink / raw)
To: Quentin Monnet, Alexei Starovoitov, Daniel Borkmann,
Andrii Nakryiko, Martin KaFai Lau, Eduard Zingerman,
Kumar Kartikeya Dwivedi, Song Liu, Yonghong Song, Jiri Olsa,
Nathan Chancellor, Bill Wendling, Justin Stitt, Emil Tsalapatis,
Ihor Solodrai, Nick Desaulniers
Cc: linux-kernel, bpf, llvm, Mark Korenberg
From: Mark Korenberg <socketpair@gmail.com>
libLLVM is only needed for "bpftool prog dump jited", yet it is a hard
dependency of bpftool: on Fedora 43, installing the ~730 KiB bpftool pulls
in ~140 MiB of llvm20-libs.
Move the LLVM disassembler to a plugin, $(libdir)/bpftool/bpftool-llvm.so,
that bpftool loads with dlopen() only when disassembling JITed programs.
Distributions can then ship it as an optional package.
The plugin exports a single structure of callbacks, with an ABI version
checked by bpftool. bpftool looks for the plugin in its install directory,
then next to its own binary, but not in the current directory since it
usually runs as root. "bpftool version" reports "llvm" only if the plugin
can be loaded.
If libLLVM is static, as required for a static bpftool, the disassembler is
linked into bpftool as before.
Link: https://github.com/libbpf/bpftool/issues/262
Signed-off-by: Mark Korenberg <socketpair@gmail.com>
---
tools/bpf/bpftool/Makefile | 38 +++++++++-
tools/bpf/bpftool/jit_disasm.c | 161 ++++++++++++++++++++++++++++------------
tools/bpf/bpftool/llvm_disasm.c | 84 +++++++++++++++++++++
tools/bpf/bpftool/llvm_disasm.h | 41 ++++++++++
tools/bpf/bpftool/main.c | 3 +-
tools/bpf/bpftool/main.h | 3 +
6 files changed, 279 insertions(+), 51 deletions(-)
diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
index b0f7168e7943..dc8e4be86296 100644
--- a/tools/bpf/bpftool/Makefile
+++ b/tools/bpf/bpftool/Makefile
@@ -63,6 +63,7 @@ $(LIBBPF_BOOTSTRAP)-clean: FORCE | $(LIBBPF_BOOTSTRAP_OUTPUT)
$(Q)$(MAKE) -C $(BPF_DIR) OUTPUT=$(LIBBPF_BOOTSTRAP_OUTPUT) clean >/dev/null
prefix ?= /usr/local
+libdir ?= $(prefix)/lib
bash_compdir ?= /usr/share/bash-completion/completions
CFLAGS += -O2
@@ -170,7 +171,7 @@ include $(wildcard $(OUTPUT)*.d)
all: $(OUTPUT)bpftool
-SRCS := $(wildcard *.c)
+SRCS := $(filter-out llvm_disasm.c,$(wildcard *.c))
ifeq ($(feature-llvm),1)
ifneq ($(SKIP_LLVM),1)
@@ -186,10 +187,19 @@ ifeq ($(HAS_LLVM),1)
# Makefile includes lib.mk which sets -D_GNU_SOURCE) which would cause
# compilation error due to redefinition. Let's filter it out here.
CFLAGS += $(filter-out -D_GNU_SOURCE,$(shell $(LLVM_CONFIG) --cflags))
- LIBS += $(shell $(LLVM_CONFIG) --libs $(LLVM_CONFIG_LIB_COMPONENTS))
+ LLVM_LIBS := $(shell $(LLVM_CONFIG) --libs $(LLVM_CONFIG_LIB_COMPONENTS))
ifeq ($(shell $(LLVM_CONFIG) --shared-mode),static)
+ # No libLLVM.so dependency to avoid, link the disassembler into bpftool
+ SRCS += llvm_disasm.c
+ LIBS += $(LLVM_LIBS)
LIBS += $(shell $(LLVM_CONFIG) --system-libs $(LLVM_CONFIG_LIB_COMPONENTS))
LIBS += -lstdc++
+ else
+ # Build the disassembler as a plugin, the only object linked against
+ # libLLVM, that bpftool loads only to disassemble JITed programs
+ LLVM_PLUGIN := $(OUTPUT)bpftool-llvm.so
+ CFLAGS += -DLLVM_PLUGIN_DIR='"$(libdir)/bpftool"'
+ LIBS += -ldl
endif
LDFLAGS += $(shell $(LLVM_CONFIG) --ldflags)
else
@@ -290,6 +300,21 @@ $(BPFTOOL_BOOTSTRAP): $(BOOTSTRAP_OBJS) $(LIBBPF_BOOTSTRAP)
$(OUTPUT)bpftool: $(OBJS) $(LIBBPF)
$(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) $(OBJS) $(LIBS) -o $@
+ifneq ($(LLVM_PLUGIN),)
+all: $(LLVM_PLUGIN)
+
+$(LLVM_PLUGIN): CFLAGS += -fPIC
+$(LLVM_PLUGIN): $(OUTPUT)llvm_disasm.o
+ $(QUIET_LINK)$(CC) $(CFLAGS) $(LDFLAGS) -shared $< $(LLVM_LIBS) -o $@
+
+# The plugin directory, $(libdir)/bpftool, is compiled into jit_disasm.o.
+# Recompile it if libdir changes, e.g. on "make" then "make install libdir=...".
+$(OUTPUT)llvm-plugin-dir: FORCE
+ $(Q)echo '$(libdir)/bpftool' | cmp -s - $@ || echo '$(libdir)/bpftool' > $@
+
+$(OUTPUT)jit_disasm.o: $(OUTPUT)llvm-plugin-dir
+endif
+
$(BOOTSTRAP_OUTPUT)%.o: %.c $(LIBBPF_BOOTSTRAP_INTERNAL_HDRS) | $(BOOTSTRAP_OUTPUT)
$(QUIET_CC)$(HOSTCC) $(HOST_CFLAGS) -c -MMD $< -o $@
@@ -303,16 +328,21 @@ feature-detect-clean:
clean: $(LIBBPF)-clean $(LIBBPF_BOOTSTRAP)-clean feature-detect-clean
$(call QUIET_CLEAN, bpftool)
$(Q)$(RM) -- $(OUTPUT)bpftool $(OUTPUT)*.o $(OUTPUT)*.d
+ $(Q)$(RM) -- $(OUTPUT)bpftool-llvm.so $(OUTPUT)llvm-plugin-dir
$(Q)$(RM) -- $(OUTPUT)*.skel.h $(OUTPUT)vmlinux.h
$(Q)$(RM) -r -- $(LIBBPF_OUTPUT) $(BOOTSTRAP_OUTPUT)
$(call QUIET_CLEAN, core-gen)
$(Q)$(RM) -- $(OUTPUT)FEATURE-DUMP.bpftool
$(Q)$(RM) -r -- $(OUTPUT)feature/
-install-bin: $(OUTPUT)bpftool
+install-bin: $(OUTPUT)bpftool $(LLVM_PLUGIN)
$(call QUIET_INSTALL, bpftool)
$(Q)$(INSTALL) -m 0755 -d $(DESTDIR)$(prefix)/sbin
$(Q)$(INSTALL) $(OUTPUT)bpftool $(DESTDIR)$(prefix)/sbin/bpftool
+ifneq ($(LLVM_PLUGIN),)
+ $(call QUIET_INSTALL, bpftool-llvm.so)
+ $(Q)$(INSTALL) -m 0755 -D -t $(DESTDIR)$(libdir)/bpftool $(LLVM_PLUGIN)
+endif
install: install-bin
$(Q)$(INSTALL) -m 0755 -d $(DESTDIR)$(bash_compdir)
@@ -321,6 +351,8 @@ install: install-bin
uninstall:
$(call QUIET_UNINST, bpftool)
$(Q)$(RM) -- $(DESTDIR)$(prefix)/sbin/bpftool
+ $(call QUIET_UNINST, bpftool-llvm.so)
+ $(Q)$(RM) -r -- $(DESTDIR)$(libdir)/bpftool
$(Q)$(RM) -- $(DESTDIR)$(bash_compdir)/bpftool
doc:
diff --git a/tools/bpf/bpftool/jit_disasm.c b/tools/bpf/bpftool/jit_disasm.c
index 5ff144ce84a1..2691252a115b 100644
--- a/tools/bpf/bpftool/jit_disasm.c
+++ b/tools/bpf/bpftool/jit_disasm.c
@@ -25,10 +25,10 @@
#include <bpf/libbpf.h>
#ifdef HAVE_LLVM_SUPPORT
-#include <llvm-c/Core.h>
-#include <llvm-c/Disassembler.h>
-#include <llvm-c/Target.h>
-#include <llvm-c/TargetMachine.h>
+#ifdef LLVM_PLUGIN_DIR
+#include <dlfcn.h>
+#endif
+#include "llvm_disasm.h"
#endif
#ifdef HAVE_LIBBFD_SUPPORT
@@ -45,7 +45,105 @@ static int oper_count;
#ifdef HAVE_LLVM_SUPPORT
#define DISASM_SPACER
-typedef LLVMDisasmContextRef disasm_ctx_t;
+typedef void *disasm_ctx_t;
+
+static const struct bpftool_llvm_ops *llvm_ops;
+
+#ifdef LLVM_PLUGIN_DIR
+#define LLVM_PLUGIN_NAME "bpftool-llvm.so"
+
+static const char *dl_error(void)
+{
+ const char *err = dlerror();
+
+ /* The error may already be consumed, e.g. by an LD_PRELOAD-ed library */
+ return err ? err : "unknown error";
+}
+
+/*
+ * Look for the plugin in its install directory, then next to the bpftool
+ * binary so that bpftool also works from its build directory. Do not look
+ * in the current directory: bpftool usually runs as root, and would then
+ * load any library planted in the directory it is run from.
+ */
+static int llvm_plugin_find(char *path, size_t size)
+{
+ char exe[PATH_MAX];
+ ssize_t len;
+ char *dir;
+ int n;
+
+ snprintf(path, size, "%s/%s", LLVM_PLUGIN_DIR, LLVM_PLUGIN_NAME);
+ if (!access(path, F_OK))
+ return 0;
+
+ len = readlink("/proc/self/exe", exe, sizeof(exe) - 1);
+ if (len < 0)
+ return -1;
+ exe[len] = '\0';
+ dir = strrchr(exe, '/');
+ if (!dir)
+ return -1;
+ *dir = '\0';
+
+ n = snprintf(path, size, "%s/%s", exe, LLVM_PLUGIN_NAME);
+ if (n < 0 || (size_t)n >= size)
+ return -1;
+ return access(path, F_OK);
+}
+
+static int llvm_load(bool verbose)
+{
+ const struct bpftool_llvm_ops *ops;
+ char path[PATH_MAX];
+ void *handle;
+
+ if (llvm_ops)
+ return 0;
+
+ if (llvm_plugin_find(path, sizeof(path))) {
+ if (verbose)
+ p_err("%s not found in %s or next to bpftool, it is required to disassemble JITed programs",
+ LLVM_PLUGIN_NAME, LLVM_PLUGIN_DIR);
+ return -1;
+ }
+
+ handle = dlopen(path, RTLD_NOW | RTLD_LOCAL);
+ if (!handle) {
+ if (verbose)
+ p_err("failed to load LLVM disassembler plugin: %s",
+ dl_error());
+ return -1;
+ }
+
+ ops = dlsym(handle, BPFTOOL_LLVM_OPS_SYM);
+ if (!ops) {
+ if (verbose)
+ p_err("invalid LLVM disassembler plugin: %s", dl_error());
+ goto err_close;
+ }
+ if (ops->abi_version != BPFTOOL_LLVM_ABI_VERSION) {
+ if (verbose)
+ p_err("%s has ABI version %u, expected %u",
+ path, ops->abi_version, BPFTOOL_LLVM_ABI_VERSION);
+ goto err_close;
+ }
+
+ /* Keep the plugin loaded until bpftool exits */
+ llvm_ops = ops;
+ return 0;
+
+err_close:
+ dlclose(handle);
+ return -1;
+}
+#else
+static int llvm_load(__maybe_unused bool verbose)
+{
+ llvm_ops = &bpftool_llvm_ops;
+ return 0;
+}
+#endif /* LLVM_PLUGIN_DIR */
static int printf_json(char *s)
{
@@ -63,48 +161,13 @@ static int printf_json(char *s)
return 0;
}
-/* This callback to set the ref_type is necessary to have the LLVM disassembler
- * print PC-relative addresses instead of byte offsets for branch instruction
- * targets.
- */
-static const char *
-symbol_lookup_callback(__maybe_unused void *disasm_info,
- __maybe_unused uint64_t ref_value,
- uint64_t *ref_type, __maybe_unused uint64_t ref_PC,
- __maybe_unused const char **ref_name)
-{
- *ref_type = LLVMDisassembler_ReferenceType_InOut_None;
- return NULL;
-}
-
static int
init_context(disasm_ctx_t *ctx, const char *arch,
__maybe_unused const char *disassembler_options,
__maybe_unused unsigned char *image, __maybe_unused ssize_t len,
__maybe_unused __u64 func_ksym)
{
- char *triple;
-
- if (arch)
- triple = LLVMNormalizeTargetTriple(arch);
- else
- triple = LLVMGetDefaultTargetTriple();
- if (!triple) {
- p_err("Failed to retrieve triple");
- return -1;
- }
-
- /*
- * Enable all aarch64 ISA extensions so the disassembler can handle any
- * instruction the kernel JIT might emit (e.g. ARM64 LSE atomics).
- */
- if (!strncmp(triple, "aarch64", 7))
- *ctx = LLVMCreateDisasmCPUFeatures(triple, "", "+all", NULL, 0, NULL,
- symbol_lookup_callback);
- else
- *ctx = LLVMCreateDisasm(triple, NULL, 0, NULL, symbol_lookup_callback);
- LLVMDisposeMessage(triple);
-
+ *ctx = llvm_ops->create_context(arch);
if (!*ctx) {
p_err("Failed to create disassembler");
return -1;
@@ -115,7 +178,7 @@ init_context(disasm_ctx_t *ctx, const char *arch,
static void destroy_context(disasm_ctx_t *ctx)
{
- LLVMDisasmDispose(*ctx);
+ llvm_ops->destroy_context(*ctx);
}
static int
@@ -125,7 +188,7 @@ disassemble_insn(disasm_ctx_t *ctx, unsigned char *image, ssize_t len, int pc,
char buf[256];
int count;
- count = LLVMDisasmInstruction(*ctx, image + pc, len - pc, func_ksym + pc,
+ count = llvm_ops->disassemble(*ctx, image + pc, len - pc, func_ksym + pc,
buf, sizeof(buf));
if (json_output)
printf_json(buf);
@@ -135,12 +198,16 @@ disassemble_insn(disasm_ctx_t *ctx, unsigned char *image, ssize_t len, int pc,
return count;
}
+bool disasm_llvm_available(void)
+{
+ return !llvm_load(false);
+}
+
int disasm_init(void)
{
- LLVMInitializeAllTargetInfos();
- LLVMInitializeAllTargetMCs();
- LLVMInitializeAllDisassemblers();
- return 0;
+ if (llvm_load(true))
+ return -1;
+ return llvm_ops->init();
}
#endif /* HAVE_LLVM_SUPPORT */
diff --git a/tools/bpf/bpftool/llvm_disasm.c b/tools/bpf/bpftool/llvm_disasm.c
new file mode 100644
index 000000000000..b92df1e8966f
--- /dev/null
+++ b/tools/bpf/bpftool/llvm_disasm.c
@@ -0,0 +1,84 @@
+// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+/*
+ * libLLVM-based disassembler for JITed programs.
+ *
+ * This file is usually built as bpftool-llvm.so, the only bpftool component
+ * linked against libLLVM, which bpftool loads only when it needs to
+ * disassemble JITed programs (see jit_disasm.c). It is linked into bpftool
+ * directly when libLLVM is a static library.
+ */
+#include <string.h>
+
+#include <llvm-c/Core.h>
+#include <llvm-c/Disassembler.h>
+#include <llvm-c/Target.h>
+#include <llvm-c/TargetMachine.h>
+
+#include "llvm_disasm.h"
+
+/*
+ * This callback to set the ref_type is necessary to have the LLVM disassembler
+ * print PC-relative addresses instead of byte offsets for branch instruction
+ * targets.
+ */
+static const char *
+symbol_lookup_callback(void *disasm_info, uint64_t ref_value,
+ uint64_t *ref_type, uint64_t ref_PC,
+ const char **ref_name)
+{
+ *ref_type = LLVMDisassembler_ReferenceType_InOut_None;
+ return NULL;
+}
+
+static int llvm_init(void)
+{
+ LLVMInitializeAllTargetInfos();
+ LLVMInitializeAllTargetMCs();
+ LLVMInitializeAllDisassemblers();
+ return 0;
+}
+
+static void *llvm_create_context(const char *arch)
+{
+ LLVMDisasmContextRef ctx;
+ char *triple;
+
+ if (arch)
+ triple = LLVMNormalizeTargetTriple(arch);
+ else
+ triple = LLVMGetDefaultTargetTriple();
+ if (!triple)
+ return NULL;
+
+ /*
+ * Enable all aarch64 ISA extensions so the disassembler can handle any
+ * instruction the kernel JIT might emit (e.g. ARM64 LSE atomics).
+ */
+ if (!strncmp(triple, "aarch64", 7))
+ ctx = LLVMCreateDisasmCPUFeatures(triple, "", "+all", NULL, 0, NULL,
+ symbol_lookup_callback);
+ else
+ ctx = LLVMCreateDisasm(triple, NULL, 0, NULL, symbol_lookup_callback);
+ LLVMDisposeMessage(triple);
+
+ return ctx;
+}
+
+static void llvm_destroy_context(void *ctx)
+{
+ LLVMDisasmDispose(ctx);
+}
+
+static size_t llvm_disassemble(void *ctx, uint8_t *bytes, uint64_t size,
+ uint64_t pc, char *buf, size_t buf_size)
+{
+ return LLVMDisasmInstruction(ctx, bytes, size, pc, buf, buf_size);
+}
+
+const struct bpftool_llvm_ops bpftool_llvm_ops = {
+ .abi_version = BPFTOOL_LLVM_ABI_VERSION,
+ .init = llvm_init,
+ .create_context = llvm_create_context,
+ .destroy_context = llvm_destroy_context,
+ .disassemble = llvm_disassemble,
+};
diff --git a/tools/bpf/bpftool/llvm_disasm.h b/tools/bpf/bpftool/llvm_disasm.h
new file mode 100644
index 000000000000..34123a80df02
--- /dev/null
+++ b/tools/bpf/bpftool/llvm_disasm.h
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) */
+#ifndef __BPFTOOL_LLVM_DISASM_H
+#define __BPFTOOL_LLVM_DISASM_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+/*
+ * Interface between bpftool and its libLLVM-based JIT disassembler.
+ *
+ * The disassembler is usually built as a plugin, bpftool-llvm.so, that
+ * bpftool loads with dlopen(); bpftool then looks up the
+ * BPFTOOL_LLVM_OPS_SYM symbol in it. The plugin can come from a different
+ * build than the bpftool binary, so bump BPFTOOL_LLVM_ABI_VERSION on any
+ * incompatible change to struct bpftool_llvm_ops, and always keep
+ * abi_version as its first member.
+ */
+#define BPFTOOL_LLVM_ABI_VERSION 1U
+#define BPFTOOL_LLVM_OPS_SYM "bpftool_llvm_ops"
+
+struct bpftool_llvm_ops {
+ unsigned int abi_version;
+ /* Initialize libLLVM targets and disassemblers. Returns 0 on success. */
+ int (*init)(void);
+ /*
+ * Create a disassembler context for @arch, or for the host if @arch
+ * is NULL. Returns NULL on failure.
+ */
+ void *(*create_context)(const char *arch);
+ void (*destroy_context)(void *ctx);
+ /*
+ * Disassemble the instruction at @bytes, located at address @pc, into
+ * @buf. Returns the size of the instruction, or 0 if it is invalid.
+ */
+ size_t (*disassemble)(void *ctx, uint8_t *bytes, uint64_t size,
+ uint64_t pc, char *buf, size_t buf_size);
+};
+
+extern const struct bpftool_llvm_ops bpftool_llvm_ops;
+
+#endif /* __BPFTOOL_LLVM_DISASM_H */
diff --git a/tools/bpf/bpftool/main.c b/tools/bpf/bpftool/main.c
index d15fec71b64e..321e928d651c 100644
--- a/tools/bpf/bpftool/main.c
+++ b/tools/bpf/bpftool/main.c
@@ -124,7 +124,8 @@ static int do_version(int argc, char **argv)
const bool has_libbfd = false;
#endif
#ifdef HAVE_LLVM_SUPPORT
- const bool has_llvm = true;
+ /* The LLVM disassembler may be a plugin that is not installed */
+ const bool has_llvm = disasm_llvm_available();
#else
const bool has_llvm = false;
#endif
diff --git a/tools/bpf/bpftool/main.h b/tools/bpf/bpftool/main.h
index b1eb4b5d991b..96d7b147aa9d 100644
--- a/tools/bpf/bpftool/main.h
+++ b/tools/bpf/bpftool/main.h
@@ -214,6 +214,9 @@ static inline int disasm_init(void)
return -1;
}
#endif
+#ifdef HAVE_LLVM_SUPPORT
+bool disasm_llvm_available(void);
+#endif
void print_data_json(uint8_t *data, size_t len);
void print_hex_data_json(uint8_t *data, size_t len);
--
2.56.0
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH bpf-next v2 2/2] bpftool: Make the LLVM disassembler an optional runtime dependency
2026-10-29 12:43 ` [PATCH bpf-next v2 2/2] bpftool: Make the LLVM disassembler an optional runtime dependency Mark Korenberg via B4 Relay
@ 2026-10-29 12:54 ` sashiko-bot
0 siblings, 0 replies; 4+ messages in thread
From: sashiko-bot @ 2026-10-29 12:54 UTC (permalink / raw)
To: Mark Korenberg; +Cc: bpf
Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] bpftool: llvm_plugin_find() misses staged plugins and prefers system plugin
--
commit aa662f293876360fc9cf9139e86022f88a5bbb64
Author: Mark Korenberg <socketpair@gmail.com>
bpftool: Make the LLVM disassembler an optional runtime dependency
This commit moves the libLLVM-based JIT disassembler into an optional
shared library plugin (bpftool-llvm.so) loaded on demand via dlopen()
when disassembling JITed programs or checking feature availability.
Link: https://github.com/libbpf/bpftool/issues/262
> diff --git a/tools/bpf/bpftool/jit_disasm.c b/tools/bpf/bpftool/jit_disasm.c
> index 5ff144ce84a1c..2691252a115b9 100644
> --- a/tools/bpf/bpftool/jit_disasm.c
> +++ b/tools/bpf/bpftool/jit_disasm.c
[ ... ]
> @@ -45,7 +45,105 @@ static int oper_count;
[ ... ]
> +/*
> + * Look for the plugin in its install directory, then next to the bpftool
> + * binary so that bpftool also works from its build directory. Do not look
> + * in the current directory: bpftool usually runs as root, and would then
> + * load any library planted in the directory it is run from.
> + */
> +static int llvm_plugin_find(char *path, size_t size)
> +{
> + char exe[PATH_MAX];
> + ssize_t len;
> + char *dir;
> + int n;
> +
> + snprintf(path, size, "%s/%s", LLVM_PLUGIN_DIR, LLVM_PLUGIN_NAME);
> + if (!access(path, F_OK))
> + return 0;
> +
> + len = readlink("/proc/self/exe", exe, sizeof(exe) - 1);
> + if (len < 0)
> + return -1;
> + exe[len] = '\0';
> + dir = strrchr(exe, '/');
> + if (!dir)
> + return -1;
> + *dir = '\0';
> +
> + n = snprintf(path, size, "%s/%s", exe, LLVM_PLUGIN_NAME);
> + if (n < 0 || (size_t)n >= size)
> + return -1;
> + return access(path, F_OK);
> +}
[Severity: Medium]
Can llvm_plugin_find() fail to locate bpftool-llvm.so when bpftool is
installed into a staging directory via DESTDIR, such as in the BPF
selftests build?
In tools/testing/selftests/bpf/Makefile, $(DEFAULT_BPFTOOL) and
$(CROSS_BPFTOOL) are built and staged with:
tools/testing/selftests/bpf/Makefile:
$(Q)$(MAKE) $(submake_extras) -C $(BPFTOOLDIR) \
...
OUTPUT=$(HOST_BUILD_DIR)/bpftool/ \
...
prefix= DESTDIR=$(HOST_SCRATCH_DIR)/ install-bin
Because prefix= is empty and libdir is not overridden, tools/bpf/bpftool/Makefile
sets libdir to /lib and compiles jit_disasm.o with:
tools/bpf/bpftool/Makefile:
prefix ?= /usr/local
libdir ?= $(prefix)/lib
...
CFLAGS += -DLLVM_PLUGIN_DIR='"$(libdir)/bpftool"'
Meanwhile, the install-bin target places the binary and plugin in separate
directories under $(DESTDIR):
tools/bpf/bpftool/Makefile:
install-bin: $(OUTPUT)bpftool $(LLVM_PLUGIN)
$(call QUIET_INSTALL, bpftool)
$(Q)$(INSTALL) -m 0755 -d $(DESTDIR)$(prefix)/sbin
$(Q)$(INSTALL) $(OUTPUT)bpftool $(DESTDIR)$(prefix)/sbin/bpftool
ifneq ($(LLVM_PLUGIN),)
$(call QUIET_INSTALL, bpftool-llvm.so)
$(Q)$(INSTALL) -m 0755 -D -t $(DESTDIR)$(libdir)/bpftool $(LLVM_PLUGIN)
endif
This installs bpftool to $(HOST_SCRATCH_DIR)/sbin/bpftool and the plugin to
$(HOST_SCRATCH_DIR)/lib/bpftool/bpftool-llvm.so. When the staged bpftool
runs, llvm_plugin_find() checks /lib/bpftool/bpftool-llvm.so and
$(HOST_SCRATCH_DIR)/sbin/bpftool-llvm.so, missing the staged plugin in
$(HOST_SCRATCH_DIR)/lib/bpftool/bpftool-llvm.so (causing "bpftool prog dump
jited" to fail and "bpftool version" to omit the llvm feature).
Additionally, because llvm_plugin_find() checks LLVM_PLUGIN_DIR before the
directory of /proc/self/exe, wouldn't running an uninstalled ./bpftool from
its build directory on a host where $(LLVM_PLUGIN_DIR)/bpftool-llvm.so is
already installed load the system plugin instead of ./bpftool-llvm.so next
to the binary (and fail without falling back if the installed plugin has a
different BPFTOOL_LLVM_ABI_VERSION or incompatible sanitizer flags)?
--
Sashiko AI review · https://sashiko.dev/#/patchset/20261029-bpftool-plugin-v2-0-1a47b2391b0b@gmail.com?part=2
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2026-10-29 12:54 UTC | newest]
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2026-10-29 12:43 [PATCH bpf-next v2 0/2] bpftool: Make the LLVM disassembler an optional runtime dependency Mark Korenberg via B4 Relay
2026-10-29 12:43 ` [PATCH bpf-next v2 1/2] bpftool: Fix disposal of the LLVM disassembler context Mark Korenberg via B4 Relay
2026-10-29 12:43 ` [PATCH bpf-next v2 2/2] bpftool: Make the LLVM disassembler an optional runtime dependency Mark Korenberg via B4 Relay
2026-10-29 12:54 ` sashiko-bot
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