linux-kernel - [PATCH] objtool: Do not retrieve data from empty sections

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Date:   Thu, 14 Sep 2017 12:11:11 -0700
From:   Petr Vandrovec <petr@...are.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
CC:     <linux-kernel@...r.kernel.org>, <akpm@...ux-foundation.org>
Subject: [PATCH] objtool: Do not retrieve data from empty sections

From: Petr Vandrovec <petr@...drovec.name>

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@...drovec.name>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
---
 tools/objtool/elf.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 6e9f980a7d26..99eccd23023d 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 */
-- 
2.14.1