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Subject[PATCH] objtool: Do not retrieve data from empty sections
From: Petr Vandrovec <petr@vandrovec.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@vandrovec.name>
Cc: Josh Poimboeuf <jpoimboe@redhat.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
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