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kdb: Cleanup math with KDB_CMD_HISTORY_COUNT

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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>
Link: https://lore.kernel.org/r/20200507161125.1.I2cce9ac66e141230c3644b8174b6c15d4e769232@changeid
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
This commit is contained in:
Douglas Anderson 2020-05-07 16:11:46 -07:00 committed by Daniel Thompson
parent 195867ffea
commit 1b310030bb
1 changed files with 2 additions and 1 deletions
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kernel/debug/kdb/kdb_main.c
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@ -1108,7 +1108,8 @@ static int handle_ctrl_cmd(char *cmd)
switch (*cmd) { switch (*cmd) {
case CTRL_P: case CTRL_P:
if (cmdptr != cmd_tail) 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); strscpy(cmd_cur, cmd_hist[cmdptr], CMD_BUFLEN);
return 1; return 1;
case CTRL_N: case CTRL_N: