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: 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 patch. Denis Orlov (1): MIPS: fix optimised memset returning garbage arch/mips/lib/memset.S | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) -- 2.20.1 _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox
There is a subtle bug in arch/mips/lib/memset.S, which results in not writing the correct return value into v0 register if the value to fill memory with is 0. Signed-off-by: Denis Orlov <denorl2009@gmail.com> --- arch/mips/lib/memset.S | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/mips/lib/memset.S b/arch/mips/lib/memset.S index 0b81bd7d8d..cd4e4ccfe8 100644 --- a/arch/mips/lib/memset.S +++ b/arch/mips/lib/memset.S @@ -34,8 +34,8 @@ */ LEAF(memset) - beqz a1, 1f move v0, a0 /* result */ + beqz a1, 1f andi a1, 0xff /* spread fillword */ LONG_SLL t1, a1, 8 -- 2.20.1 _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox
On Thu, 10 Mar 2022 16:40:39 +0300 Denis Orlov <denorl2009@gmail.com> wrote: Hi Denis! I'm very glad to see that you have found this anoying bug! Some tips: * you comment from "PATCH 0/1" is very informative but after applying "PATCH 1/1" to the mainline this very informative comment remain in maillist archive but not in the barebox git repo; Could you please combine "PATCH 0/1" comment and "PATCH 1/1" comment and resend single "PATCH v2" ? * I propose this ammendment for your comment: > --- a/PATCH-0/1 > +++ b/PATCH-0/1 > @@ -108,8 +108,8 @@ List-Archive: <https://lore.barebox.org/barebox/> > 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 > +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: -- Best regards, Antony Pavlov > 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: > 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 > patch. > > Denis Orlov (1): > MIPS: fix optimised memset returning garbage > > arch/mips/lib/memset.S | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > -- > 2.20.1 > > > _______________________________________________ > barebox mailing list > barebox@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/barebox _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox
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@gmail.com> --- arch/mips/lib/memset.S | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/mips/lib/memset.S b/arch/mips/lib/memset.S index 0b81bd7d8d..cd4e4ccfe8 100644 --- a/arch/mips/lib/memset.S +++ b/arch/mips/lib/memset.S @@ -34,8 +34,8 @@ */ LEAF(memset) - beqz a1, 1f move v0, a0 /* result */ + beqz a1, 1f andi a1, 0xff /* spread fillword */ LONG_SLL t1, a1, 8 -- 2.20.1 _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox
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@gmail.com> > --- > arch/mips/lib/memset.S | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) Applied, thanks Sascha -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox