[PATCH 0/1] MIPS: fix optimised memset returning garbage

Denis Orlov denorl2009 at gmail.com
Thu Mar 10 05:40:39 PST 2022

There is currently a bug in memset implementation from
arch/mips/lib/memset.S that is used when MIPS_OPTIMIZED_STRING_FUNCTIONS
option is enabled. It stems from a missing '.set noreorder' directive
before the first branch. This results in an assembler stuffing a 'nop'
instruction in a 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:

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

Denis Orlov (1):
  MIPS: fix optimised memset returning garbage

 arch/mips/lib/memset.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)


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