| Message ID | 20221020123704.91203-7-quentin@isovalent.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | BPF |
| Headers | show |
| Series | bpftool: Add LLVM as default library for disassembling JIT-ed programs | expand |
On Thu, Oct 20, 2022 at 5:37 AM Quentin Monnet <quentin@isovalent.com> wrote: > > + > +/* 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; > +} Could you give an example before/after for asm that contains 'call foo' instructions? I'm not sure that above InOut_None will not break symbolization.
2022-10-20 10:49 UTC-0700 ~ Alexei Starovoitov <alexei.starovoitov@gmail.com> > On Thu, Oct 20, 2022 at 5:37 AM Quentin Monnet <quentin@isovalent.com> wrote: >> >> + >> +/* 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; >> +} > > Could you give an example before/after for asm > that contains 'call foo' instructions? > I'm not sure that above InOut_None will not break > symbolization. Hi Alexei, I ran a quick test and it doesn't seem we lose any information. Building from: #include <linux/bpf.h> #include "bpf_helper_defs.h" #define SEC(name) __attribute__((section(name), used)) static __attribute__((noinline)) int bar(int b) { return bpf_get_prandom_u32() > b; } SEC("xdp") int foo(struct xdp_md *ctx) { void *data = (void *)(long)ctx->data; void *data_end = (void *)(long)ctx->data_end; return bar(data_end - data); } Here is the output from the existing version (using libbfd): # bpftool version bpftool v7.1.0 using libbpf v1.1 features: libbfd, libbpf_strict, skeletons # bpftool prog dump jited name foo int foo(struct xdp_md * ctx): bpf_prog_65e359e7b0251046_foo: ; void *data = (void *)(long)ctx->data; 0: nopl 0x0(%rax,%rax,1) 5: xchg %ax,%ax 7: push %rbp 8: mov %rsp,%rbp b: mov 0x0(%rdi),%rsi ; void *data_end = (void *)(long)ctx->data_end; f: mov 0x8(%rdi),%rdi ; return bar(data_end - data); 13: sub %esi,%edi ; return bar(data_end - data); 15: call 0x0000000000000038 ; return bar(data_end - data); 1a: leave 1b: ret int bar(int b): bpf_prog_9b001d67a67f01cc_bar: ; int bar(int b) { 0: nopl 0x0(%rax,%rax,1) 5: xchg %ax,%ax 7: push %rbp 8: mov %rsp,%rbp b: push %rbx c: mov %edi,%ebx ; return bpf_get_prandom_u32() > b; e: call 0xffffffffcab00454 13: mov %eax,%edi 15: mov $0x1,%eax ; return bpf_get_prandom_u32() > b; 1a: cmp %ebx,%edi 1c: ja 0x0000000000000020 1e: xor %eax,%eax ; return bpf_get_prandom_u32() > b; 20: pop %rbx 21: leave 22: ret Did you expect "bar" to appear on insn '15:'? I don't think we get this from bpftool at the moment? Or did I misunderstand your question? The output from LLVM's disassembler comes below: # ./bpftool version bpftool v7.1.0 using libbpf v1.1 features: llvm, libbpf_strict, skeletons # ./bpftool prog dump jited name foo int foo(struct xdp_md * ctx): bpf_prog_65e359e7b0251046_foo: ; void *data = (void *)(long)ctx->data; 0: nopl (%rax,%rax) 5: nop 7: pushq %rbp 8: movq %rsp, %rbp b: movq (%rdi), %rsi ; void *data_end = (void *)(long)ctx->data_end; f: movq 8(%rdi), %rdi ; return bar(data_end - data); 13: subl %esi, %edi ; return bar(data_end - data); 15: callq 0x38 ; return bar(data_end - data); 1a: leave 1b: retq int bar(int b): bpf_prog_9b001d67a67f01cc_bar: ; int bar(int b) { 0: nopl (%rax,%rax) 5: nop 7: pushq %rbp 8: movq %rsp, %rbp b: pushq %rbx c: movl %edi, %ebx ; return bpf_get_prandom_u32() > b; e: callq 0xffffffffcab00454 13: movl %eax, %edi 15: movl $1, %eax ; return bpf_get_prandom_u32() > b; 1a: cmpl %ebx, %edi 1c: ja 0x20 1e: xorl %eax, %eax ; return bpf_get_prandom_u32() > b; 20: popq %rbx 21: leave 22: retq LLVM, but _without_ the LLVMDisassembler_ReferenceType_InOut_None: int foo(struct xdp_md * ctx): bpf_prog_65e359e7b0251046_foo: ; void *data = (void *)(long)ctx->data; 0: nopl (%rax,%rax) 5: nop 7: pushq %rbp 8: movq %rsp, %rbp b: movq (%rdi), %rsi ; void *data_end = (void *)(long)ctx->data_end; f: movq 8(%rdi), %rdi ; return bar(data_end - data); 13: subl %esi, %edi ; return bar(data_end - data); 15: callq 30 ; return bar(data_end - data); 1a: leave 1b: retq int bar(int b): bpf_prog_9b001d67a67f01cc_bar: ; int bar(int b) { 0: nopl (%rax,%rax) 5: nop 7: pushq %rbp 8: movq %rsp, %rbp b: pushq %rbx c: movl %edi, %ebx ; return bpf_get_prandom_u32() > b; e: callq -894434239 13: movl %eax, %edi 15: movl $1, %eax ; return bpf_get_prandom_u32() > b; 1a: cmpl %ebx, %edi 1c: ja 2 1e: xorl %eax, %eax ; return bpf_get_prandom_u32() > b; 20: popq %rbx 21: leave 22: retq
On Mon, Oct 24, 2022 at 4:05 AM Quentin Monnet <quentin@isovalent.com> wrote: > > 2022-10-20 10:49 UTC-0700 ~ Alexei Starovoitov > <alexei.starovoitov@gmail.com> > > On Thu, Oct 20, 2022 at 5:37 AM Quentin Monnet <quentin@isovalent.com> wrote: > >> > >> + > >> +/* 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; > >> +} > > > > Could you give an example before/after for asm > > that contains 'call foo' instructions? > > I'm not sure that above InOut_None will not break > > symbolization. > > Hi Alexei, I ran a quick test and it doesn't seem we lose any > information. Building from: Thanks for checking. The output looks good.
On Mon, Oct 24, 2022 at 11:40 AM Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote: > > On Mon, Oct 24, 2022 at 4:05 AM Quentin Monnet <quentin@isovalent.com> wrote: > > > > 2022-10-20 10:49 UTC-0700 ~ Alexei Starovoitov > > <alexei.starovoitov@gmail.com> > > > On Thu, Oct 20, 2022 at 5:37 AM Quentin Monnet <quentin@isovalent.com> wrote: > > >> > > >> + > > >> +/* 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; > > >> +} > > > > > > Could you give an example before/after for asm > > > that contains 'call foo' instructions? > > > I'm not sure that above InOut_None will not break > > > symbolization. > > > > Hi Alexei, I ran a quick test and it doesn't seem we lose any > > information. Building from: > > Thanks for checking. The output looks good. Please rebase. It doesn't apply anymore.
diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile index 1c81f4d514bb..787b857d3fb5 100644 --- a/tools/bpf/bpftool/Makefile +++ b/tools/bpf/bpftool/Makefile @@ -95,6 +95,7 @@ RM ?= rm -f FEATURE_USER = .bpftool FEATURE_TESTS := clang-bpf-co-re +FEATURE_TESTS += llvm FEATURE_TESTS += libcap FEATURE_TESTS += libbfd FEATURE_TESTS += libbfd-liberty @@ -103,6 +104,7 @@ 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 @@ -137,27 +139,37 @@ all: $(OUTPUT)bpftool 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 -endif +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 + # 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 + # 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 -ifeq ($(filter -DHAVE_LIBBFD_SUPPORT,$(CFLAGS)),) +ifeq ($(filter -DHAVE_LLVM_SUPPORT -DHAVE_LIBBFD_SUPPORT,$(CFLAGS)),) # No support for JIT disassembly SRCS := $(filter-out jit_disasm.c,$(SRCS)) endif diff --git a/tools/bpf/bpftool/jit_disasm.c b/tools/bpf/bpftool/jit_disasm.c index e31ad3950fd6..c28b21f90cb9 100644 --- a/tools/bpf/bpftool/jit_disasm.c +++ b/tools/bpf/bpftool/jit_disasm.c @@ -20,18 +20,123 @@ #include <stdlib.h> #include <unistd.h> #include <string.h> -#include <bfd.h> -#include <dis-asm.h> #include <sys/stat.h> #include <limits.h> #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> +#endif + +#ifdef HAVE_LIBBFD_SUPPORT +#include <bfd.h> +#include <dis-asm.h> #include <tools/dis-asm-compat.h> +#endif #include "json_writer.h" #include "main.h" static int oper_count; +#ifdef HAVE_LLVM_SUPPORT +#define DISASM_SPACER + +typedef LLVMDisasmContextRef disasm_ctx_t; + +static int printf_json(char *s) +{ + s = strtok(s, " \t"); + jsonw_string_field(json_wtr, "operation", s); + + jsonw_name(json_wtr, "operands"); + jsonw_start_array(json_wtr); + oper_count = 1; + + while ((s = strtok(NULL, " \t,()")) != 0) { + jsonw_string(json_wtr, s); + oper_count++; + } + 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) +{ + char *triple; + + if (arch) { + p_err("Architecture %s not supported", arch); + return -1; + } + + triple = LLVMGetDefaultTargetTriple(); + if (!triple) { + p_err("Failed to retrieve triple"); + return -1; + } + *ctx = LLVMCreateDisasm(triple, NULL, 0, NULL, symbol_lookup_callback); + LLVMDisposeMessage(triple); + + if (!*ctx) { + p_err("Failed to create disassembler"); + return -1; + } + + return 0; +} + +static void destroy_context(disasm_ctx_t *ctx) +{ + LLVMDisposeMessage(*ctx); +} + +static int +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, pc, + buf, sizeof(buf)); + if (json_output) + printf_json(buf); + else + printf("%s", buf); + + return count; +} + +int disasm_init(void) +{ + LLVMInitializeNativeTarget(); + LLVMInitializeNativeDisassembler(); + return 0; +} +#endif /* HAVE_LLVM_SUPPORT */ + +#ifdef HAVE_LIBBFD_SUPPORT +#define DISASM_SPACER "\t" + typedef struct { struct disassemble_info *info; disassembler_ftype disassemble; @@ -210,6 +315,7 @@ int disasm_init(void) bfd_init(); return 0; } +#endif /* HAVE_LIBBPFD_SUPPORT */ int disasm_print_insn(unsigned char *image, ssize_t len, int opcodes, const char *arch, const char *disassembler_options, @@ -252,7 +358,7 @@ int disasm_print_insn(unsigned char *image, ssize_t len, int opcodes, if (linfo) btf_dump_linfo_plain(btf, linfo, "; ", linum); - printf("%4x:\t", pc); + printf("%4x:" DISASM_SPACER, pc); } count = disassemble_insn(&ctx, image, len, pc); diff --git a/tools/bpf/bpftool/main.h b/tools/bpf/bpftool/main.h index c9e171082cf6..9a149c67aa5d 100644 --- a/tools/bpf/bpftool/main.h +++ b/tools/bpf/bpftool/main.h @@ -172,7 +172,7 @@ int map_parse_fds(int *argc, char ***argv, int **fds); int map_parse_fd_and_info(int *argc, char ***argv, void *info, __u32 *info_len); struct bpf_prog_linfo; -#ifdef HAVE_LIBBFD_SUPPORT +#if defined(HAVE_LLVM_SUPPORT) || defined(HAVE_LIBBFD_SUPPORT) int disasm_print_insn(unsigned char *image, ssize_t len, int opcodes, const char *arch, const char *disassembler_options, const struct btf *btf, @@ -193,7 +193,7 @@ int disasm_print_insn(unsigned char *image, ssize_t len, int opcodes, } static inline int disasm_init(void) { - p_err("No libbfd support"); + p_err("No JIT disassembly support"); return -1; } #endif
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. For building bpftool, we have to detect how the libbfd version on the system behaves, which is why we have to handle features disassembler-four-args and disassembler-init-styled in the Makefile. When it comes to shipping bpftool, this has also caused issues with several distribution maintainers unwilling to support the feature (see for example Debian's page for binutils-dev, which ships libbfd: "Note that building Debian packages which depend on the shared libbfd is Not Allowed." [0]). For these reasons, we add support for LLVM as an alternative to libbfd for disassembling instructions of JIT-ed programs. Thanks to the preparation work in the previous commits, it's easy to add the library by passing the relevant compilation options in the Makefile, and by adding the functions for setting up the LLVM disassembler in file jit_disasm.c. The LLVM disassembler requires the LLVM development package (usually llvm-dev or llvm-devel). The expectation is that the interface for this disassembler will be more stable. There is a note in LLVM's Developer Policy [1] stating that the stability for the C API is "best effort" and not guaranteed, but at least there is some effort to keep compatibility when possible (which hasn't really been the case for libbfd so far). Furthermore, the Debian page for the related LLVM package does not caution against linking to the lib, as binutils-dev page does. Naturally, the display of disassembled instructions comes with a few minor differences. Here is a sample output with libbfd (already supported before this patch): # bpftool prog dump jited id 56 bpf_prog_6deef7357e7b4530: 0: nopl 0x0(%rax,%rax,1) 5: xchg %ax,%ax 7: push %rbp 8: mov %rsp,%rbp b: push %rbx c: push %r13 e: push %r14 10: mov %rdi,%rbx 13: movzwq 0xb4(%rbx),%r13 1b: xor %r14d,%r14d 1e: or $0x2,%r14d 22: mov $0x1,%eax 27: cmp $0x2,%r14 2b: jne 0x000000000000002f 2d: xor %eax,%eax 2f: pop %r14 31: pop %r13 33: pop %rbx 34: leave 35: ret LLVM supports several variants that we could set when initialising the disassembler, for example with: LLVMSetDisasmOptions(*ctx, LLVMDisassembler_Option_AsmPrinterVariant); but the default printer is used for now. Here is the output with LLVM: # bpftool prog dump jited id 56 bpf_prog_6deef7357e7b4530: 0: nopl (%rax,%rax) 5: nop 7: pushq %rbp 8: movq %rsp, %rbp b: pushq %rbx c: pushq %r13 e: pushq %r14 10: movq %rdi, %rbx 13: movzwq 180(%rbx), %r13 1b: xorl %r14d, %r14d 1e: orl $2, %r14d 22: movl $1, %eax 27: cmpq $2, %r14 2b: jne 0x2f 2d: xorl %eax, %eax 2f: popq %r14 31: popq %r13 33: popq %rbx 34: leave 35: retq The LLVM disassembler comes as the default choice, with libbfd as a fall-back. Of course, we could replace libbfd entirely and avoid supporting two different libraries. One reason for keeping libbfd is that, right now, 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 motivation is that libbfd supports nfp instruction for Netronome's SmartNICs and can be used to disassemble offloaded programs, something that LLVM cannot do. If libbfd's interface breaks again in the future, we might reconsider keeping support for it. [0] https://packages.debian.org/buster/binutils-dev [1] https://llvm.org/docs/DeveloperPolicy.html#c-api-changes Signed-off-by: Quentin Monnet <quentin@isovalent.com> Tested-by: Niklas Söderlund <niklas.soderlund@corigine.com> Acked-by: Yonghong Song <yhs@fb.com> --- tools/bpf/bpftool/Makefile | 46 +++++++++----- tools/bpf/bpftool/jit_disasm.c | 112 ++++++++++++++++++++++++++++++++- tools/bpf/bpftool/main.h | 4 +- 3 files changed, 140 insertions(+), 22 deletions(-)