On 2022-07-28 13:27, Siddhesh Poyarekar wrote:
Interesting, I'll take a closer look at this from the gcc context. I
obviously don't have any strong opinions about the elfutils patch :)
I reduced this to the below program and I see it warns with
`-D_FORTIFY_SOURCE=3 -O2 -fsanitize=undefined` as well as
`-D_FORTIFY_SOURCE=2 -O2 -fsanitize=undefined`. This is definitely a
false positive on unreachable code; __pread_alias will never be called
when nbytes is greater than object size.
So I can confirm that this is harmless.
Sid
~~~
typedef long ssize_t;
typedef unsigned long size_t;
typedef long off_t;
struct ar_hdr
{
char ar_mode;
char ar_size[10];
};
extern ssize_t __pread_chk (int fd, void *buf, size_t nbytes, off_t offset,
size_t bufsize)
__attribute__((__access__ (__write_only__, 2, 3)));
extern ssize_t __pread_alias (int fd, void *buf, size_t nbytes, off_t
offset)
__attribute__((__access__ (__write_only__, 2, 3)));
extern ssize_t __pread_chk_warn (int fd, void *buf, size_t nbytes,
off_t offset, size_t bufsize);
extern __inline __attribute__((__always_inline__))
__attribute__((__gnu_inline__)) ssize_t
pread (int fd, void *buf, size_t nbytes, off_t offset)
{
size_t osz = __builtin_dynamic_object_size (buf, 0);
if (__builtin_constant_p (osz) && osz == (size_t) -1)
return __pread_alias (fd, buf, nbytes, offset);
return (((__typeof (nbytes)) 0 < (__typeof (nbytes)) - 1
|| (__builtin_constant_p (nbytes) && (nbytes) > 0))
&& __builtin_constant_p (nbytes <= osz / 1)
&& nbytes <= osz / 1)
? __pread_alias (fd, buf, nbytes, offset)
: __pread_chk (fd, buf, nbytes, offset, osz);
}
ssize_t
pread_retry (int fd, off_t start_offset, off_t offset)
{
ssize_t recvd = 0;
struct ar_hdr h = {.ar_size = {0} };
void *buf = h.ar_size;
size_t len = sizeof (h.ar_size);
off_t off =
start_offset + offset + __builtin_offsetof (struct ar_hdr, ar_size);
do
{
long int res;
do
{
res = pread (fd, ((char *) buf) + recvd, len - recvd, off +
recvd);
}
while (res == -1L);
recvd += res;
}
while ((size_t) recvd < len);
return recvd;
}
