From: Douglas Anderson <dianders@chromium.org>
To: Jason Wessel <jason.wessel@windriver.com>,
Daniel Thompson <daniel.thompson@linaro.org>
Cc: sumit.garg@linaro.org, Douglas Anderson <dianders@chromium.org>,
Chuhong Yuan <hslester96@gmail.com>,
Dan Carpenter <dan.carpenter@oracle.com>,
Masahiro Yamada <yamada.masahiro@socionext.com>,
kgdb-bugreport@lists.sourceforge.net,
linux-kernel@vger.kernel.org
Subject: [PATCH] kdb: Cleanup math with KDB_CMD_HISTORY_COUNT
Date: Thu, 7 May 2020 16:11:46 -0700 [thread overview]
Message-ID: <20200507161125.1.I2cce9ac66e141230c3644b8174b6c15d4e769232@changeid> (raw)
From code inspection the math in handle_ctrl_cmd() looks super sketchy
because it subjects -1 from cmdptr and then does a "%
KDB_CMD_HISTORY_COUNT". It turns out that this code works because
"cmdptr" is unsigned and KDB_CMD_HISTORY_COUNT is a nice power of 2.
Let's make this a little less sketchy.
This patch should be a no-op.
Signed-off-by: Douglas Anderson <dianders@chromium.org>
---
kernel/debug/kdb/kdb_main.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 515379cbf209..6865a0f58d38 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -1108,7 +1108,8 @@ static int handle_ctrl_cmd(char *cmd)
switch (*cmd) {
case CTRL_P:
if (cmdptr != cmd_tail)
- cmdptr = (cmdptr-1) % KDB_CMD_HISTORY_COUNT;
+ cmdptr = (cmdptr + KDB_CMD_HISTORY_COUNT - 1) %
+ KDB_CMD_HISTORY_COUNT;
strscpy(cmd_cur, cmd_hist[cmdptr], CMD_BUFLEN);
return 1;
case CTRL_N:
--
2.26.2.645.ge9eca65c58-goog
next reply other threads:[~2020-05-07 23:12 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-07 23:11 Douglas Anderson [this message]
2020-05-08 12:02 ` [PATCH] kdb: Cleanup math with KDB_CMD_HISTORY_COUNT Sumit Garg
2020-05-20 16:08 ` Daniel Thompson
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