[PATCH V2 1/5] Add dso__is_pie call to identify ELF PIE

[Steve Clevenger <scclevenger@os.amperecomputing.com>]

Changes in V2:
  - Updated mailing list distribution
  - Decrease indentation, add null pointer checks per Leo Yan review

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 Clevenger <scclevenger@os.amperecomputing.com>
---
 tools/perf/util/symbol-elf.c | 60 ++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index e398abfd13a0..0e49c1345a67 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -662,6 +662,66 @@ 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))
+		goto exit;	// false
+
+	dso__build_id_filename(dso, dso_path, sizeof(dso_path), false);
+
+	fd = open(dso_path, O_RDONLY);
+
+	if (fd < 0) {
+		pr_debug("%s: cannot read cached %s.\n", __func__, dso_path);
+		goto exit;	// false
+	}
+
+	elf = elf_begin(fd, ELF_C_READ, NULL);
+	gelf_getehdr(elf, &ehdr);
+
+	if (ehdr.e_type == ET_DYN) {
+		Elf_Data *data;
+		GElf_Dyn *entry;
+		int n_entries = shdr.sh_size / sizeof(GElf_Dyn);
+
+		scn = elf_section_by_name(elf, &ehdr, &shdr, ".dynamic", NULL);
+		if (!scn)
+			goto exit;	// false
+
+		data = (Elf_Data *) elf_getdata(scn, NULL);
+		if (!data || !data->d_buf)
+			goto exit;	// false
+
+		// check DT_FLAGS_1
+		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);
+exit:
+	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
-- 
2.25.1