[PATCH v9 3/3] perf annotate: LLVM-based disassembler

Steinar H. Gunderson
2024-07-19T15:01:10Z

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@google.com>
---
tools/perf/util/disasm.c | 193 +++++++++++++++++++++++++++++
tools/perf/util/llvm-c-helpers.cpp | 62 +++++++++
tools/perf/util/llvm-c-helpers.h | 11 ++
3 files changed, 266 insertions(+)

diff --git a/tools/perf/util/disasm.c b/tools/perf/util/disasm.c
index 9be2becfe6e8..f0232ce3d751 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 +1611,189 @@ 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 = disinfo;
+
+ 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;
+ int ret = -1;
+
+ 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);
+ 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;
+ }
+
+ ret = 0;
+
+err:
+ LLVMDisasmDispose(disasm);
+ free(buf);
+ free(line_storage);
+ return ret;
+}
+#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 +1918,11 @@ 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
--
2.45.2