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[PATCH] bfd: Fix warning when compiling with clang, fix buglet
- From: Simon Marchi <simon dot marchi at ericsson dot com>
- To: <binutils at sourceware dot org>
- Cc: Simon Marchi <simon dot marchi at ericsson dot com>
- Date: Tue, 30 Jan 2018 18:02:39 -0500
- Subject: [PATCH] bfd: Fix warning when compiling with clang, fix buglet
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I would like to fix instances of the following warning, when building
with clang with no special CFLAGS other than -g3 -O0.
/home/emaisin/src/binutils-gdb/bfd/elflink.c:5425:45: error: performing pointer arithmetic on a null pointer has undefined behavior [-Werror,-Wnull-pointer-arithmetic]
return (struct elf_link_hash_entry *) 0 - 1;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^
Replacing those with "(struct elf_link_hash_entry *) -1" gets rid of the
warning. I wanted to check that it didn't change the resulting code, so
I tried to build this:
$ cat test.c
int *before()
{
return (int *) 0 - 1;
}
int *after()
{
return (int *) - 1;
}
$ gcc -c test.c -g
$ objdump -d test.o
test.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <before>:
0: 55 push %rbp
1: 48 89 e5 mov %rsp,%rbp
4: 48 c7 c0 fc ff ff ff mov $0xfffffffffffffffc,%rax
b: 5d pop %rbp
c: c3 retq
000000000000000d <after>:
d: 55 push %rbp
e: 48 89 e5 mov %rsp,%rbp
11: 48 c7 c0 ff ff ff ff mov $0xffffffffffffffff,%rax
18: 5d pop %rbp
19: c3 retq
This shows that the previous code doesn't actually return -1 as the
function documentation says, but the new one does, so it's kind of a
bugfix.
bfd/ChangeLog:
* elf64-ppc.c (ppc64_elf_archive_symbol_lookup): Remove pointer
arithmetic on NULL pointer.
* elflink.c (_bfd_elf_archive_symbol_lookup,
elf_link_add_archive_symbols): Likewise.
---
bfd/elf64-ppc.c | 2 +-
bfd/elflink.c | 4 ++--
2 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/bfd/elf64-ppc.c b/bfd/elf64-ppc.c
index 5cbb035..9e4a4b5 100644
--- a/bfd/elf64-ppc.c
+++ b/bfd/elf64-ppc.c
@@ -5051,7 +5051,7 @@ ppc64_elf_archive_symbol_lookup (bfd *abfd,
len = strlen (name);
dot_name = bfd_alloc (abfd, len + 2);
if (dot_name == NULL)
- return (struct elf_link_hash_entry *) 0 - 1;
+ return (struct elf_link_hash_entry *) -1;
dot_name[0] = '.';
memcpy (dot_name + 1, name, len + 1);
h = _bfd_elf_archive_symbol_lookup (abfd, info, dot_name);
diff --git a/bfd/elflink.c b/bfd/elflink.c
index f1ec880..1de8e78 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -5422,7 +5422,7 @@ _bfd_elf_archive_symbol_lookup (bfd *abfd,
len = strlen (name);
copy = (char *) bfd_alloc (abfd, len);
if (copy == NULL)
- return (struct elf_link_hash_entry *) 0 - 1;
+ return (struct elf_link_hash_entry *) -1;
first = p - name + 1;
memcpy (copy, name, first);
@@ -5520,7 +5520,7 @@ elf_link_add_archive_symbols (bfd *abfd, struct bfd_link_info *info)
}
h = archive_symbol_lookup (abfd, info, symdef->name);
- if (h == (struct elf_link_hash_entry *) 0 - 1)
+ if (h == (struct elf_link_hash_entry *) -1)
goto error_return;
if (h == NULL)
--
2.7.4