arm-cs-trace-disasm.py/perf must accommodate non-zero DSO text offset

From: "steve.c.clevenger.ampere" <[email protected]>

Add dso__is_pie global to read the .dynamic section DT_FLAGS_1 entry for the DF_1_PIE flag. This identifies position executable code.

Signed-off-by steve.c.clevenger.ampere <[email protected]>

---
 tools/perf/util/symbol-elf.c | 55 ++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

tools/perf/util/symbol-elf.c +20 -0

index e398abfd13a0..1d4bd222b314 100644
@@ -662,6 +662,61 @@ static int dso__synthesize_plt_got_symbols(struct dso *dso, Elf *elf,
 	return err;
 }
 
+/*
+ * Check dynamic section DT_FLAGS_1 for a Position Independent
+ * Executable (PIE).
+ */
+bool dso__is_pie(struct dso *dso)
+{
+	Elf *elf = NULL;
+	Elf_Scn *scn = NULL;
+	GElf_Ehdr ehdr;
+	GElf_Shdr shdr;
+	bool is_pie = false;
+	char dso_path[PATH_MAX];
+	int fd = -1;
+
+	if (!dso || (elf_version(EV_CURRENT) == EV_NONE))
+		return is_pie;	// false
+
+	dso__build_id_filename(dso, dso_path, sizeof(dso_path), false);
+
+	fd = open(dso_path, O_RDONLY);

tools/perf/util/symbol-elf.c +18 -0

+			for (int i = 0; i < n_entries; i++) {
+				entry = ((GElf_Dyn *) data->d_buf) + i;
+				if (entry->d_tag == DT_FLAGS_1) {
+					if ((entry->d_un.d_val & DF_1_PIE) != 0) {
+						is_pie = true;
+						break;
+					}
+				}
+			} // end for
+		}
+	}
+
+	elf_end(elf);
+	close(fd);
+
+	return is_pie;
+}
+
 /*
  * We need to check if we have a .dynsym, so that we can handle the
  * .plt, synthesizing its symbols, that aren't on the symtabs (be it

Signature · 1 line

2.25.1

Hi Steve,

Quoted 38 lines · Steve Clevenger

From: "steve.c.clevenger.ampere" <[email protected]>

Add dso__is_pie global to read the .dynamic section DT_FLAGS_1 entry for the DF_1_PIE flag. This identifies position executable code.

Signed-off-by steve.c.clevenger.ampere <[email protected]>

---
 tools/perf/util/symbol-elf.c | 55 ++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

tools/perf/util/symbol-elf.c +20 -0

index e398abfd13a0..1d4bd222b314 100644
@@ -662,6 +662,61 @@ static int dso__synthesize_plt_got_symbols(struct dso *dso, Elf *elf,
 	return err;
 }
 
+/*
+ * Check dynamic section DT_FLAGS_1 for a Position Independent
+ * Executable (PIE).
+ */
+bool dso__is_pie(struct dso *dso)
+{
+	Elf *elf = NULL;
+	Elf_Scn *scn = NULL;
+	GElf_Ehdr ehdr;
+	GElf_Shdr shdr;
+	bool is_pie = false;
+	char dso_path[PATH_MAX];
+	int fd = -1;
+
+	if (!dso || (elf_version(EV_CURRENT) == EV_NONE))
+		return is_pie;	// false
+
+	dso__build_id_filename(dso, dso_path, sizeof(dso_path), false);
+
+	fd = open(dso_path, O_RDONLY);

tools/perf/util/symbol-elf.c static int dso__synthesize_plt_got_symbols(struct dso *dso, Elf *elf, · line 694

Quoted 10 lines

tools/perf/util/symbol-elf.c +10 -0

+
+	if (fd < 0) {
+		pr_debug("%s: cannot read cached %s.\n", __func__, dso_path);
+		return is_pie;	// false
+	}
+
+	elf = elf_begin(fd, ELF_C_READ, NULL);
+	gelf_getehdr(elf, &ehdr);
+
+	if (ehdr.e_type == ET_DYN) {

The code looks good to me, just several nitpicks.

To avoid indentation, we can firstly check the failure case and directly exit for it.

        if (ehdr.e_type != ET_DYN)
                goto exit_elf_end;

tools/perf/util/symbol-elf.c static int dso__synthesize_plt_got_symbols(struct dso *dso, Elf *elf, · line 695

Quoted 1 line

tools/perf/util/symbol-elf.c +1 -0

+		scn = elf_section_by_name(elf, &ehdr, &shdr, ".dynamic", NULL);

Ditto.

        if (!scn)
                goto exit_elf_end;

tools/perf/util/symbol-elf.c static int dso__synthesize_plt_got_symbols(struct dso *dso, Elf *elf, · line 701

Quoted 6 lines

tools/perf/util/symbol-elf.c +6 -0

+		if (scn) {	// check DT_FLAGS_1
+			Elf_Data *data;
+			GElf_Dyn *entry;
+			int n_entries = shdr.sh_size / sizeof(GElf_Dyn);
+
+			data = (Elf_Data *) elf_getdata(scn, NULL);

For a safe code, it is good to check if pointers (data and data->d_buf) are valid before dereference them.

       if (!data || !data->d_buf)
               goto exit_elf_end;

With above changes:

Reviewed-by Leo Yan <[email protected]>

Quoted 25 lines

tools/perf/util/symbol-elf.c +18 -0

+			for (int i = 0; i < n_entries; i++) {
+				entry = ((GElf_Dyn *) data->d_buf) + i;
+				if (entry->d_tag == DT_FLAGS_1) {
+					if ((entry->d_un.d_val & DF_1_PIE) != 0) {
+						is_pie = true;
+						break;
+					}
+				}
+			} // end for
+		}
+	}
+
+	elf_end(elf);
+	close(fd);
+
+	return is_pie;
+}
+
 /*
  * We need to check if we have a .dynsym, so that we can handle the
  * .plt, synthesizing its symbols, that aren't on the symtabs (be it

Signature · 1 line

2.25.1