Re: [PATCH v7 3/4] perf annotate: LLVM-based disassembler

From: Namhyung Kim
Date: Wed May 29 2024 - 00:06:47 EST


On Sun, May 26, 2024 at 11:22 AM Steinar H. Gunderson <sesse@googlecom> wrote:
>
> Support using LLVM as a disassembler method, allowing helperless
> annotation in non-distro builds. (It is also much faster than
> using libbfd or bfd objdump on binaries with a lot of debug
> information.)
>
> This is nearly identical to the output of llvm-objdump; there are
> some very rare whitespace differences, some minor changes to demangling
> (since we use perf's regular demangling and not LLVM's own) and
> the occasional case where llvm-objdump makes a different choice
> when multiple symbols share the same address. It should work across
> all of LLVM's supported architectures, although I've only tested 64-bit
> x86, and finding the right triple from perf's idea of machine
> architecture can sometimes be a bit tricky. Ideally, we should have
> some way of finding the triplet just from the file itself.
>
> Signed-off-by: Steinar H. Gunderson <sesse@xxxxxxxxxx>
> ---
> tools/perf/util/disasm.c | 195 +++++++++++++++++++++++++++++
> tools/perf/util/llvm-c-helpers.cpp | 62 +++++++++
> tools/perf/util/llvm-c-helpers.h | 11 ++
> 3 files changed, 268 insertions(+)
>
> diff --git a/tools/perf/util/disasm.c b/tools/perf/util/disasm.c
> index c0dbb955e61a..ee7c2365d066 100644
> --- a/tools/perf/util/disasm.c
> +++ b/tools/perf/util/disasm.c
> @@ -43,6 +43,7 @@ static int call__scnprintf(struct ins *ins, char *bf, size_t size,
>
> static void ins__sort(struct arch *arch);
> static int disasm_line__parse(char *line, const char **namep, char **rawp);
> +static char *expand_tabs(char *line, char **storage, size_t *storage_len);
>
> static __attribute__((constructor)) void symbol__init_regexpr(void)
> {
> @@ -1378,7 +1379,9 @@ static int open_capstone_handle(struct annotate_args *args, bool is_64bit,
>
> return 0;
> }
> +#endif
>
> +#if defined(HAVE_LIBCAPSTONE_SUPPORT) || defined(HAVE_LIBLLVM_SUPPORT)
> struct find_file_offset_data {
> u64 ip;
> u64 offset;
> @@ -1442,7 +1445,9 @@ read_symbol(const char *filename, struct map *map, struct symbol *sym,
> free(buf);
> return NULL;
> }
> +#endif
>
> +#ifdef HAVE_LIBCAPSTONE_SUPPORT
> static void print_capstone_detail(cs_insn *insn, char *buf, size_t len,
> struct annotate_args *args, u64 addr)
> {
> @@ -1606,6 +1611,191 @@ static int symbol__disassemble_capstone(char *filename, struct symbol *sym,
> }
> #endif
>
> +#ifdef HAVE_LIBLLVM_SUPPORT
> +#include <llvm-c/Disassembler.h>
> +#include <llvm-c/Target.h>
> +#include "util/llvm-c-helpers.h"
> +
> +struct symbol_lookup_storage {
> + u64 branch_addr;
> + u64 pcrel_load_addr;
> +};
> +
> +/*
> + * Whenever LLVM wants to resolve an address into a symbol, it calls this
> + * callback. We don't ever actually _return_ anything (in particular, because
> + * it puts quotation marks around what we return), but we use this as a hint
> + * that there is a branch or PC-relative address in the expression that we
> + * should add some textual annotation for after the instruction. The caller
> + * will use this information to add the actual annotation.
> + */
> +static const char *
> +symbol_lookup_callback(void *disinfo, uint64_t value,
> + uint64_t *ref_type,
> + uint64_t address __maybe_unused,
> + const char **ref __maybe_unused)
> +{
> + struct symbol_lookup_storage *storage =
> + (struct symbol_lookup_storage *)disinfo;

You don't need this in C. :) Also we usually put a blank line
after declaration (at least, at the beginning).


> + if (*ref_type == LLVMDisassembler_ReferenceType_In_Branch)
> + storage->branch_addr = value;
> + else if (*ref_type == LLVMDisassembler_ReferenceType_In_PCrel_Load)
> + storage->pcrel_load_addr = value;
> + *ref_type = LLVMDisassembler_ReferenceType_InOut_None;
> + return NULL;
> +}
> +
> +static int symbol__disassemble_llvm(char *filename, struct symbol *sym,
> + struct annotate_args *args)
> +{
> + struct annotation *notes = symbol__annotation(sym);
> + struct map *map = args->ms.map;
> + struct dso *dso = map__dso(map);
> + u64 start = map__rip_2objdump(map, sym->start);
> + u8 *buf;
> + u64 len;
> + u64 pc;
> + bool is_64bit;
> + char triplet[64];
> + char disasm_buf[2048];
> + size_t disasm_len;
> + struct disasm_line *dl;
> + LLVMDisasmContextRef disasm = NULL;
> + struct symbol_lookup_storage storage;
> + char *line_storage = NULL;
> + size_t line_storage_len = 0;
> +
> + if (args->options->objdump_path)
> + return -1;
> +
> + LLVMInitializeAllTargetInfos();
> + LLVMInitializeAllTargetMCs();
> + LLVMInitializeAllDisassemblers();
> +
> + buf = read_symbol(filename, map, sym, &len, &is_64bit);
> + if (buf == NULL)
> + return -1;
> +
> + if (arch__is(args->arch, "x86")) {
> + if (is_64bit)
> + scnprintf(triplet, sizeof(triplet), "x86_64-pc-linux");
> + else
> + scnprintf(triplet, sizeof(triplet), "i686-pc-linux");
> + } else {
> + scnprintf(triplet, sizeof(triplet), "%s-linux-gnu",
> + args->arch->name);
> + }
> +
> + disasm = LLVMCreateDisasm(
> + triplet, &storage, 0, NULL, symbol_lookup_callback);

We put the arguments at the same line and align them.
Please do the same in other places.


> + if (disasm == NULL)
> + goto err;
> +
> + if (args->options->disassembler_style &&
> + !strcmp(args->options->disassembler_style, "intel"))
> + LLVMSetDisasmOptions(
> + disasm, LLVMDisassembler_Option_AsmPrinterVariant);
> +
> + /*
> + * This needs to be set after AsmPrinterVariant, due to a bug in LLVM;
> + * setting AsmPrinterVariant makes a new instruction printer, making it
> + * forget about the PrintImmHex flag (which is applied before if both
> + * are given to the same call).
> + */
> + LLVMSetDisasmOptions(disasm, LLVMDisassembler_Option_PrintImmHex);
> +
> + /* add the function address and name */
> + scnprintf(disasm_buf, sizeof(disasm_buf), "%#"PRIx64" <%s>:",
> + start, sym->name);
> +
> + args->offset = -1;
> + args->line = disasm_buf;
> + args->line_nr = 0;
> + args->fileloc = NULL;
> + args->ms.sym = sym;
> +
> + dl = disasm_line__new(args);
> + if (dl == NULL)
> + goto err;
> +
> + annotation_line__add(&dl->al, &notes->src->source);
> +
> + pc = start;
> + for (u64 offset = 0; offset < len; ) {
> + unsigned int ins_len;
> +
> + storage.branch_addr = 0;
> + storage.pcrel_load_addr = 0;
> +
> + ins_len = LLVMDisasmInstruction(
> + disasm, buf + offset, len - offset, pc,
> + disasm_buf, sizeof(disasm_buf));
> + if (ins_len == 0)
> + goto err;
> + disasm_len = strlen(disasm_buf);
> +
> + if (storage.branch_addr != 0) {
> + char *name = llvm_name_for_code(
> + dso, filename, storage.branch_addr);
> + if (name != NULL) {
> + disasm_len += scnprintf(
> + disasm_buf + disasm_len,
> + sizeof(disasm_buf) - disasm_len,
> + " <%s>", name);
> + free(name);
> + }
> + }
> + if (storage.pcrel_load_addr != 0) {
> + char *name = llvm_name_for_data(
> + dso, filename, storage.pcrel_load_addr);
> + disasm_len += scnprintf(disasm_buf + disasm_len,
> + sizeof(disasm_buf) - disasm_len,
> + " # %#"PRIx64,
> + storage.pcrel_load_addr);
> + if (name) {
> + disasm_len += scnprintf(
> + disasm_buf + disasm_len,
> + sizeof(disasm_buf) - disasm_len,
> + " <%s>", name);
> + free(name);
> + }
> + }
> +
> + args->offset = offset;
> + args->line = expand_tabs(
> + disasm_buf, &line_storage, &line_storage_len);
> + args->line_nr = 0;
> + args->fileloc = NULL;
> + args->ms.sym = sym;
> +
> + llvm_addr2line(filename, pc, &args->fileloc,
> + (unsigned int *)&args->line_nr, false, NULL);
> +
> + dl = disasm_line__new(args);
> + if (dl == NULL)
> + goto err;
> +
> + annotation_line__add(&dl->al, &notes->src->source);
> +
> + free(args->fileloc);
> + pc += ins_len;
> + offset += ins_len;
> + }
> +
> + LLVMDisasmDispose(disasm);
> + free(buf);
> + free(line_storage);
> + return 0;

Often we just set a different return value here and share the
error handling logic at the end.

Thanks,
Namhyung


> +
> +err:
> + LLVMDisasmDispose(disasm);
> + free(buf);
> + free(line_storage);
> + return -1;
> +}
> +#endif
> +
> +
> /*
> * Possibly create a new version of line with tabs expanded. Returns the
> * existing or new line, storage is updated if a new line is allocated. If
> @@ -1730,6 +1920,11 @@ int symbol__disassemble(struct symbol *sym, struct annotate_args *args)
> strcpy(symfs_filename, tmp);
> }
>
> +#ifdef HAVE_LIBLLVM_SUPPORT
> + err = symbol__disassemble_llvm(symfs_filename, sym, args);
> + if (err == 0)
> + goto out_remove_tmp;
> +#endif
> #ifdef HAVE_LIBCAPSTONE_SUPPORT
> err = symbol__disassemble_capstone(symfs_filename, sym, args);
> if (err == 0)
> diff --git a/tools/perf/util/llvm-c-helpers.cpp b/tools/perf/util/llvm-c-helpers.cpp
> index 3cc967ec6f28..4070e2d5682f 100644
> --- a/tools/perf/util/llvm-c-helpers.cpp
> +++ b/tools/perf/util/llvm-c-helpers.cpp
> @@ -8,6 +8,7 @@
> #pragma GCC diagnostic push
> #pragma GCC diagnostic ignored "-Wunused-parameter" /* Needed for LLVM <= 15 */
> #include <llvm/DebugInfo/Symbolize/Symbolize.h>
> +#include <llvm/Support/TargetSelect.h>
> #pragma GCC diagnostic pop
>
> #include <stdio.h>
> @@ -19,6 +20,9 @@ extern "C" {
> #include "symbol_conf.h"
> #include "llvm-c-helpers.h"
>
> +extern "C"
> +char *dso__demangle_sym(struct dso *dso, int kmodule, const char *elf_name);
> +
> using namespace llvm;
> using llvm::symbolize::LLVMSymbolizer;
>
> @@ -132,3 +136,61 @@ int llvm_addr2line(const char *dso_name, u64 addr,
> return extract_file_and_line(*res_or_err, file, line);
> }
> }
> +
> +static char *
> +make_symbol_relative_string(struct dso *dso, const char *sym_name,
> + u64 addr, u64 base_addr)
> +{
> + if (!strcmp(sym_name, "<invalid>"))
> + return NULL;
> +
> + char *demangled = dso__demangle_sym(dso, 0, sym_name);
> + if (base_addr && base_addr != addr) {
> + char buf[256];
> + snprintf(buf, sizeof(buf), "%s+0x%lx",
> + demangled ? demangled : sym_name, addr - base_addr);
> + free(demangled);
> + return strdup(buf);
> + } else {
> + if (demangled)
> + return demangled;
> + else
> + return strdup(sym_name);
> + }
> +}
> +
> +extern "C"
> +char *llvm_name_for_code(struct dso *dso, const char *dso_name, u64 addr)
> +{
> + LLVMSymbolizer *symbolizer = get_symbolizer();
> + object::SectionedAddress sectioned_addr = {
> + addr,
> + object::SectionedAddress::UndefSection
> + };
> + Expected<DILineInfo> res_or_err =
> + symbolizer->symbolizeCode(dso_name, sectioned_addr);
> + if (!res_or_err) {
> + return NULL;
> + }
> + return make_symbol_relative_string(
> + dso, res_or_err->FunctionName.c_str(),
> + addr, res_or_err->StartAddress ? *res_or_err->StartAddress : 0);
> +}
> +
> +extern "C"
> +char *llvm_name_for_data(struct dso *dso, const char *dso_name, u64 addr)
> +{
> + LLVMSymbolizer *symbolizer = get_symbolizer();
> + object::SectionedAddress sectioned_addr = {
> + addr,
> + object::SectionedAddress::UndefSection
> + };
> + Expected<DIGlobal> res_or_err =
> + symbolizer->symbolizeData(dso_name, sectioned_addr);
> + if (!res_or_err) {
> + return NULL;
> + }
> + return make_symbol_relative_string(
> + dso, res_or_err->Name.c_str(),
> + addr, res_or_err->Start);
> +}
> diff --git a/tools/perf/util/llvm-c-helpers.h b/tools/perf/util/llvm-c-helpers.h
> index 19332dd98e14..d2b99637a28a 100644
> --- a/tools/perf/util/llvm-c-helpers.h
> +++ b/tools/perf/util/llvm-c-helpers.h
> @@ -13,6 +13,8 @@
> extern "C" {
> #endif
>
> +struct dso;
> +
> struct llvm_a2l_frame {
> char* filename;
> char* funcname;
> @@ -42,6 +44,15 @@ int llvm_addr2line(const char* dso_name,
> bool unwind_inlines,
> struct llvm_a2l_frame** inline_frames);
>
> +/*
> + * Simple symbolizers for addresses; will convert something like
> + * 0x12345 to "func+0x123". Will return NULL if no symbol was found.
> + *
> + * The returned value must be freed by the caller, with free().
> + */
> +char *llvm_name_for_code(struct dso *dso, const char *dso_name, u64 addr);
> +char *llvm_name_for_data(struct dso *dso, const char *dso_name, u64 addr);
> +
> #ifdef __cplusplus
> }
> #endif
> --
> 2.45.1
>
>