[PATCH v2 09/17] perf dso: Move read_symbol from llvm/capstone to dso

Ian Rogers
2025-01-22T06:25:03Z

Move the read_symbol function to dso.h, make the return type const and
add a mutable out_buf out parameter. In future changes this will allow
a code pointer to be returned without necessary allocating memory.

Signed-off-by: Ian Rogers <irogers@google.com>
---
tools/perf/util/capstone.c | 64 +++++-----------------------
tools/perf/util/dso.c | 67 +++++++++++++++++++++++++++++
tools/perf/util/dso.h | 4 ++
tools/perf/util/llvm.c | 87 +++++++-------------------------------
4 files changed, 97 insertions(+), 125 deletions(-)

diff --git a/tools/perf/util/capstone.c b/tools/perf/util/capstone.c
index 8d65c7a55a8b..f103988184c8 100644
--- a/tools/perf/util/capstone.c
+++ b/tools/perf/util/capstone.c
@@ -434,66 +434,23 @@ static int find_file_offset(u64 start, u64 len, u64 pgoff, void *arg)
return 0;
}

-static u8 *
-read_symbol(const char *filename, struct map *map, struct symbol *sym,
- u64 *len, bool *is_64bit)
-{
- struct dso *dso = map__dso(map);
- struct nscookie nsc;
- u64 start = map__rip_2objdump(map, sym->start);
- u64 end = map__rip_2objdump(map, sym->end);
- int fd, count;
- u8 *buf = NULL;
- struct find_file_offset_data data = {
- .ip = start,
- };
-
- *is_64bit = false;
-
- nsinfo__mountns_enter(dso__nsinfo(dso), &nsc);
- fd = open(filename, O_RDONLY);
- nsinfo__mountns_exit(&nsc);
- if (fd < 0)
- return NULL;
-
- if (file__read_maps(fd, /*exe=*/true, find_file_offset, &data,
- is_64bit) == 0)
- goto err;
-
- *len = end - start;
- buf = malloc(*len);
- if (buf == NULL)
- goto err;
-
- count = pread(fd, buf, *len, data.offset);
- close(fd);
- fd = -1;
-
- if ((u64)count != *len)
- goto err;
-
- return buf;
-
-err:
- if (fd >= 0)
- close(fd);
- free(buf);
- return NULL;
-}
-
int symbol__disassemble_capstone(const char *filename __maybe_unused,
struct symbol *sym __maybe_unused,
struct annotate_args *args __maybe_unused)
{
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);
- u64 len;
u64 offset;
int i, count, free_count;
bool is_64bit = false;
bool needs_cs_close = false;
- u8 *buf = NULL;
+ /* Malloc-ed buffer containing instructions read from disk. */
+ u8 *code_buf = NULL;
+ /* Pointer to code to be disassembled. */
+ const u8 *buf;
+ u64 buf_len;
csh handle;
struct cs_insn *insn = NULL;
char disasm_buf[512];
@@ -503,7 +460,8 @@ int symbol__disassemble_capstone(const char *filename __maybe_unused,
if (args->options->objdump_path)
return -1;

- buf = read_symbol(filename, map, sym, &len, &is_64bit);
+ buf = dso__read_symbol(dso, filename, map, sym,
+ &code_buf, &buf_len, &is_64bit);
if (buf == NULL)
return -1;

@@ -532,7 +490,7 @@ int symbol__disassemble_capstone(const char *filename __maybe_unused,

needs_cs_close = true;

- free_count = count = perf_cs_disasm(handle, buf, len, start, len, &insn);
+ free_count = count = perf_cs_disasm(handle, buf, buf_len, start, buf_len, &insn);
for (i = 0, offset = 0; i < count; i++) {
int printed;

@@ -556,7 +514,7 @@ int symbol__disassemble_capstone(const char *filename __maybe_unused,
}

/* It failed in the middle: probably due to unknown instructions */
- if (offset != len) {
+ if (offset != buf_len) {
struct list_head *list = &notes->src->source;

/* Discard all lines and fallback to objdump */
@@ -575,7 +533,7 @@ int symbol__disassemble_capstone(const char *filename __maybe_unused,
if (free_count > 0)
perf_cs_free(insn, free_count);
}
- free(buf);
+ free(code_buf);
return count < 0 ? count : 0;

err:
diff --git a/tools/perf/util/dso.c b/tools/perf/util/dso.c
index 5c6e85fdae0d..0285904ed26d 100644
--- a/tools/perf/util/dso.c
+++ b/tools/perf/util/dso.c
@@ -1664,3 +1664,70 @@ bool is_perf_pid_map_name(const char *dso_name)

return perf_pid_map_tid(dso_name, &tid);
}
+
+struct find_file_offset_data {
+ u64 ip;
+ u64 offset;
+};
+
+/* This will be called for each PHDR in an ELF binary */
+static int find_file_offset(u64 start, u64 len, u64 pgoff, void *arg)
+{
+ struct find_file_offset_data *data = arg;
+
+ if (start <= data->ip && data->ip < start + len) {
+ data->offset = pgoff + data->ip - start;
+ return 1;
+ }
+ return 0;
+}
+
+const u8 *dso__read_symbol(struct dso *dso, const char *symfs_filename,
+ const struct map *map, const struct symbol *sym,
+ u8 **out_buf, u64 *out_buf_len, bool *is_64bit)
+{
+ struct nscookie nsc;
+ u64 start = map__rip_2objdump(map, sym->start);
+ u64 end = map__rip_2objdump(map, sym->end);
+ int fd, count;
+ u8 *buf = NULL;
+ size_t len;
+ struct find_file_offset_data data = {
+ .ip = start,
+ };
+
+ *out_buf = NULL;
+ *out_buf_len = 0;
+ *is_64bit = false;
+
+ nsinfo__mountns_enter(dso__nsinfo(dso), &nsc);
+ fd = open(symfs_filename, O_RDONLY);
+ nsinfo__mountns_exit(&nsc);
+ if (fd < 0)
+ return NULL;
+
+ if (file__read_maps(fd, /*exe=*/true, find_file_offset, &data, is_64bit) == 0)
+ goto err;
+
+ len = end - start;
+ buf = malloc(len);
+ if (buf == NULL)
+ goto err;
+
+ count = pread(fd, buf, len, data.offset);
+ close(fd);
+ fd = -1;
+
+ if ((u64)count != len)
+ goto err;
+
+ *out_buf = buf;
+ *out_buf_len = len;
+ return buf;
+
+err:
+ if (fd >= 0)
+ close(fd);
+ free(buf);
+ return NULL;
+}
diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
index bb8e8f444054..734e3a3d95f0 100644
--- a/tools/perf/util/dso.h
+++ b/tools/perf/util/dso.h
@@ -828,4 +828,8 @@ u64 dso__findnew_global_type(struct dso *dso, u64 addr, u64 offset);
bool perf_pid_map_tid(const char *dso_name, int *tid);
bool is_perf_pid_map_name(const char *dso_name);

+const u8 *dso__read_symbol(struct dso *dso, const char *symfs_filename,
+ const struct map *map, const struct symbol *sym,
+ u8 **out_buf, u64 *out_buf_len, bool *is_64bit);
+
#endif /* __PERF_DSO */
diff --git a/tools/perf/util/llvm.c b/tools/perf/util/llvm.c
index f6a8943b7c9d..a0774373f0d6 100644
--- a/tools/perf/util/llvm.c
+++ b/tools/perf/util/llvm.c
@@ -296,71 +296,6 @@ void dso__free_a2l_llvm(struct dso *dso __maybe_unused)
/* Nothing to free. */
}

-
-struct find_file_offset_data {
- u64 ip;
- u64 offset;
-};
-
-/* This will be called for each PHDR in an ELF binary */
-static int find_file_offset(u64 start, u64 len, u64 pgoff, void *arg)
-{
- struct find_file_offset_data *data = arg;
-
- if (start <= data->ip && data->ip < start + len) {
- data->offset = pgoff + data->ip - start;
- return 1;
- }
- return 0;
-}
-
-static u8 *
-read_symbol(const char *filename, struct map *map, struct symbol *sym,
- u64 *len, bool *is_64bit)
-{
- struct dso *dso = map__dso(map);
- struct nscookie nsc;
- u64 start = map__rip_2objdump(map, sym->start);
- u64 end = map__rip_2objdump(map, sym->end);
- int fd, count;
- u8 *buf = NULL;
- struct find_file_offset_data data = {
- .ip = start,
- };
-
- *is_64bit = false;
-
- nsinfo__mountns_enter(dso__nsinfo(dso), &nsc);
- fd = open(filename, O_RDONLY);
- nsinfo__mountns_exit(&nsc);
- if (fd < 0)
- return NULL;
-
- if (file__read_maps(fd, /*exe=*/true, find_file_offset, &data,
- is_64bit) == 0)
- goto err;
-
- *len = end - start;
- buf = malloc(*len);
- if (buf == NULL)
- goto err;
-
- count = pread(fd, buf, *len, data.offset);
- close(fd);
- fd = -1;
-
- if ((u64)count != *len)
- goto err;
-
- return buf;
-
-err:
- if (fd >= 0)
- close(fd);
- free(buf);
- return NULL;
-}
-
/*
* Whenever LLVM wants to resolve an address into a symbol, it calls this
* callback. We don't ever actually _return_ anything (in particular, because
@@ -397,8 +332,11 @@ int symbol__disassemble_llvm(const char *filename, struct symbol *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;
+ /* Malloc-ed buffer containing instructions read from disk. */
+ u8 *code_buf = NULL;
+ /* Pointer to code to be disassembled. */
+ const u8 *buf;
+ u64 buf_len;
u64 pc;
bool is_64bit;
char triplet[64];
@@ -418,7 +356,8 @@ int symbol__disassemble_llvm(const char *filename, struct symbol *sym,
perf_LLVMInitializeAllTargetMCs();
perf_LLVMInitializeAllDisassemblers();

- buf = read_symbol(filename, map, sym, &len, &is_64bit);
+ buf = dso__read_symbol(dso, filename, map, sym,
+ &code_buf, &buf_len, &is_64bit);
if (buf == NULL)
return -1;

@@ -466,14 +405,18 @@ int symbol__disassemble_llvm(const char *filename, struct symbol *sym,
annotation_line__add(&dl->al, &notes->src->source);

pc = start;
- for (u64 offset = 0; offset < len; ) {
+ for (u64 offset = 0; offset < buf_len; ) {
unsigned int ins_len;

storage.branch_addr = 0;
storage.pcrel_load_addr = 0;

- ins_len = perf_LLVMDisasmInstruction(disasm, buf + offset,
- len - offset, pc,
+ /*
+ * LLVM's API has the code be disassembled as non-const, cast
+ * here as we may be disassembling from mapped read-only memory.
+ */
+ ins_len = perf_LLVMDisasmInstruction(disasm, (u8 *)(buf + offset),
+ buf_len - offset, pc,
disasm_buf, sizeof(disasm_buf));
if (ins_len == 0)
goto err;
@@ -531,7 +474,7 @@ int symbol__disassemble_llvm(const char *filename, struct symbol *sym,

err:
perf_LLVMDisasmDispose(disasm);
- free(buf);
+ free(code_buf);
free(line_storage);
return ret;