From: Siddhesh Poyarekar <siddhesh@gotplt.org>
To: Mark Wielaard <mark@klomp.org>, elfutils-devel@sourceware.org
Subject: Re: [PATCH] libdwfl: Rewrite reading of ar_size in elf_begin_rand
Date: Fri, 29 Jul 2022 12:31:10 -0400 [thread overview]
Message-ID: <64196909-f1ae-3c54-5485-8e89f1dba9c8@gotplt.org> (raw)
In-Reply-To: <fe190da2-4341-efac-10f4-9de893b19b1b@gotplt.org>
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;
}
next prev parent reply other threads:[~2022-07-29 16:31 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-28 13:48 Mark Wielaard
2022-07-28 13:54 ` Mark Wielaard
2022-07-28 17:27 ` Siddhesh Poyarekar
2022-07-29 16:31 ` Siddhesh Poyarekar [this message]
2022-07-29 18:34 ` Mark Wielaard
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