On 9/9/24 10:29 AM, Alexei Starovoitov wrote:
On Mon, Sep 9, 2024 at 10:21 AM Zac Ecob <zacecob@xxxxxxxxxxxxxx> wrote:
Hello,
I recently received a kernel 'oops' about a divide error.
After some research, it seems that the 'div64_s64' function used for the 'MOD'/'REM' instructions boils down to an 'idiv'.
The 'dividend' is set to INT64_MIN, and the 'divisor' to -1, then because of two's complement, there is no corresponding positive value, causing the error (at least to my understanding).
Apologies if this is already known / not a relevant concern.
Thanks for the report. This is a new issue.
Yonghong,
it's related to the new signed div insn.
It sounds like we need to update chk_and_div[] part of
the verifier to account for signed div differently.
In verifier, we have
/* [R,W]x div 0 -> 0 */
/* [R,W]x mod 0 -> [R,W]x */
What the value for
Rx_a sdiv Rx_b -> ?
where Rx_a = INT64_MIN and Rx_b = -1?
Should we just do
INT64_MIN sdiv -1 -> -1
or some other values?
