objtool: Do not retrieve data from empty sections

Binutils 2.29-9 in Debian return an error when elf_getdata is invoked
on empty section (.note.GNU-stack in all kernel files), causing
immediate failure of kernel build with:

  elf_getdata: can't manipulate null section

As nothing is done with sections that have zero size, just do not
retrieve their data at all.

Signed-off-by: Petr Vandrovec <petr@vandrovec.name>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/2ce30a44349065b70d0f00e71e286dc0cbe745e6.1505459652.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 13 insertions, 12 deletions

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 1e89a5f8bfc9..b4cd8bc62521 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -175,19 +175,20 @@ static int read_sections(struct elf *elf)
                         return -1;
                 }
 
-                sec->data = elf_getdata(s, NULL);
-                if (!sec->data) {
-                        WARN_ELF("elf_getdata");
-                        return -1;
-                }
-
-                if (sec->data->d_off != 0 ||
-                    sec->data->d_size != sec->sh.sh_size) {
-                        WARN("unexpected data attributes for %s", sec->name);
-                        return -1;
+                if (sec->sh.sh_size != 0) {
+                        sec->data = elf_getdata(s, NULL);
+                        if (!sec->data) {
+                                WARN_ELF("elf_getdata");
+                                return -1;
+                        }
+                        if (sec->data->d_off != 0 ||
+                            sec->data->d_size != sec->sh.sh_size) {
+                                WARN("unexpected data attributes for %s",
+                                     sec->name);
+                                return -1;
+                        }
                 }
-
-                sec->len = sec->data->d_size;
+                sec->len = sec->sh.sh_size;
         }
 
         /* sanity check, one more call to elf_nextscn() should return NULL */