Linux-IIO Archive mirror
 help / color / mirror / Atom feed
From: Chenyuan Yang <chenyuan0y@gmail.com>
To: mazziesaccount@gmail.com, jic23@kernel.org, lars@metafoo.de,
	 linux-iio@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, Zijie Zhao <zzjas98@gmail.com>
Subject: [drivers/iio] Question about `iio_gts_build_avail_time_table`
Date: Mon, 11 Mar 2024 14:48:50 -0500	[thread overview]
Message-ID: <CALGdzur-rsLbd4BcgtR9QV2=ZH8xHAVySjm2z2TT=Aog74mdPw@mail.gmail.com> (raw)

[-- Attachment #1: Type: text/plain, Size: 1845 bytes --]

Dear Linux Developers for IIO Driver,

We are curious about the functionality of
`iio_gts_build_avail_time_table`
(https://elixir.bootlin.com/linux/latest/source/drivers/iio/industrialio-gts-helper.c#L363)

```
static int iio_gts_build_avail_time_table(struct iio_gts *gts)
{
  int *times, i, j, idx = 0, *int_micro_times;

  if (!gts->num_itime)
    return 0;

  times = kcalloc(gts->num_itime, sizeof(int), GFP_KERNEL);
  if (!times)
    return -ENOMEM;

  /* Sort times from all tables to one and remove duplicates */
  for (i = gts->num_itime - 1; i >= 0; i--) {
    int new = gts->itime_table[i].time_us;

    if (times[idx] < new) {
      times[idx++] = new;
      continue;
    }

    for (j = 0; j <= idx; j++) {
      if (times[j] > new) {
        memmove(&times[j + 1], &times[j],
                                (idx - j) * sizeof(int));
        times[j] = new;
        idx++;
      }
    }
  ...
}
```

For this function, we are trying to understand how it works but not
sure how this sorting is done.

1. When the gts->itime_table[i].time_us is zero, e.g., the time
sequence is `3, 0, 1`, the inner for-loop will not terminate and do
out-of-bound writes. This is because once `times[j] > new`, the value
`new` will be added in the current position and the `times[j]` will be
moved to `j+1` position, which makes the if-condition always hold.
Meanwhile, idx will be added one, making the loop keep running without
termination and out-of-bound write.
2. If none of the gts->itime_table[i].time_us is zero, the elements
will just be copied without being sorted as described in the comment
"Sort times from all tables to one and remove duplicates".

Please correct us if we miss some key prerequisites for this function
or the data structure.
Thanks in advance!

A possible patch based on our understanding is attached.

Best,
Chenyuan

[-- Attachment #2: iio.patch --]
[-- Type: application/octet-stream, Size: 763 bytes --]

diff --git a/drivers/iio/industrialio-gts-helper.c b/drivers/iio/industrialio-gts-helper.c
index 7653261d2dc2..0667da988295 100644
--- a/drivers/iio/industrialio-gts-helper.c
+++ b/drivers/iio/industrialio-gts-helper.c
@@ -375,19 +375,17 @@ static int iio_gts_build_avail_time_table(struct iio_gts *gts)
 	for (i = gts->num_itime - 1; i >= 0; i--) {
 		int new = gts->itime_table[i].time_us;
 
-		if (times[idx] < new) {
-			times[idx++] = new;
-			continue;
-		}
+		times[idx] = new;
 
 		for (j = 0; j <= idx; j++) {
 			if (times[j] > new) {
 				memmove(&times[j + 1], &times[j],
 					(idx - j) * sizeof(int));
 				times[j] = new;
-				idx++;
+				break;
 			}
 		}
+		idx++;
 	}
 
 	/* create a list of times formatted as list of IIO_VAL_INT_PLUS_MICRO */

             reply	other threads:[~2024-03-11 19:49 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-03-11 19:48 Chenyuan Yang [this message]
2024-03-12 11:16 ` [drivers/iio] Question about `iio_gts_build_avail_time_table` Matti Vaittinen
2024-03-12 16:53   ` Chenyuan Yang
2024-03-13  8:08     ` Matti Vaittinen

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CALGdzur-rsLbd4BcgtR9QV2=ZH8xHAVySjm2z2TT=Aog74mdPw@mail.gmail.com' \
    --to=chenyuan0y@gmail.com \
    --cc=jic23@kernel.org \
    --cc=lars@metafoo.de \
    --cc=linux-iio@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mazziesaccount@gmail.com \
    --cc=zzjas98@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).