[PATCH v2] MIPS: fix optimised memset returning garbage

Sascha Hauer s.hauer at pengutronix.de
Mon Mar 14 02:03:01 PDT 2022

On Thu, Mar 10, 2022 at 11:42:06PM +0300, Denis Orlov wrote:
> There is a subtle bug in arch/mips/lib/memset.S, used if option
> MIPS_OPTIMIZED_STRING_FUNCTIONS is enabled, which results in not writing
> the correct return value into v0 register if the value to fill memory
> with is 0.
> The bug stems from a missing '.set noreorder' directive before the first
> beqz instruction. This results in an assembler stuffing a 'nop'
> instruction in the beqz delay slot instead of an instruction writing the
> return value into v0 register that was supposed to go there. That leads
> to an error that appears when reading memory from SPI Flash and that was
> mentioned here:
> http://lists.infradead.org/pipermail/barebox/2021-June/036557.html
> There are a few ways of fixing this bug. The directive '.set noreorder'
> that shows up a bit later in code could be moved up and placed right
> before the memset label (as it was originally in Linux codebase - see
> a583158c9ce822c96a718fbf877cec1e5f9ad75d). Or, rather, the move and the
> branch instruction could be swapped, thus allowing the assembler to
> properly place move in delay slot (as it is done in Linux now - see
> 68dec269ee29c3abfd09596fbee7e40d875a6ab3) - that is what is done in this
> patch.
> Signed-off-by: Denis Orlov <denorl2009 at gmail.com>
> ---
>  arch/mips/lib/memset.S | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Applied, thanks


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