target/riscv/insn32.decode | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
If LQ has func3==010 and is located in the MISC-MEM opcodes,
then it conflicts with the CBO opcode space.
However, since LQ is specified as: "LQ is added to the MISC-MEM major
opcode", we have an implementation bug, because 'major opcode'
refers to func3, which must be 111.
This results in the following instruction encodings:
lq ........ ........ .111.... .0001111
cbo_clean 00000000 0001.... .0100000 00001111
cbo_flush 00000000 0010.... .0100000 00001111
cbo_inval 00000000 0000.... .0100000 00001111
cbo_zero 00000000 0100.... .0100000 00001111
^^^-func3
^^^^^^^-opcode
Signed-off-by: Christoph Muellner <cmuellner@linux.com>
---
target/riscv/insn32.decode | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/target/riscv/insn32.decode b/target/riscv/insn32.decode
index 5bbedc254c..d3f798ca10 100644
--- a/target/riscv/insn32.decode
+++ b/target/riscv/insn32.decode
@@ -168,7 +168,7 @@ sraw 0100000 ..... ..... 101 ..... 0111011 @r
# *** RV128I Base Instruction Set (in addition to RV64I) ***
ldu ............ ..... 111 ..... 0000011 @i
-lq ............ ..... 010 ..... 0001111 @i
+lq ............ ..... 111 ..... 0001111 @i
sq ............ ..... 100 ..... 0100011 @s
addid ............ ..... 000 ..... 1011011 @i
sllid 000000 ...... ..... 001 ..... 1011011 @sh6
--
2.34.1
Le 18/01/2022 à 17:32, Christoph Muellner a écrit : > If LQ has func3==010 and is located in the MISC-MEM opcodes, > then it conflicts with the CBO opcode space. > However, since LQ is specified as: "LQ is added to the MISC-MEM major > opcode", we have an implementation bug, because 'major opcode' > refers to func3, which must be 111. > > This results in the following instruction encodings: > > lq ........ ........ .111.... .0001111 > cbo_clean 00000000 0001.... .0100000 00001111 > cbo_flush 00000000 0010.... .0100000 00001111 > cbo_inval 00000000 0000.... .0100000 00001111 > cbo_zero 00000000 0100.... .0100000 00001111 > ^^^-func3 > ^^^^^^^-opcode Hello Christoph, I see page table 26.1 of the last riscv-isa-manual.pdf what is called major opcodes in my understanding, and MISC-MEM is one of them with value 00_111_11. The value for func3 that I chose comes from https://github.com/michaeljclark/riscv-meta/blob/master/opcodes which admittedly is out-dated, but I don't see any particular value for LQ/SQ in the new spec either (I mean, riscv-isa-manual.pdf, any pointer we could refer to ?). I have nothing against changing the opcode, but then we need to change disas/riscv.c which also uses the previous opcode to dump instructions when running with -d in_asm. Frédéric > > Signed-off-by: Christoph Muellner <cmuellner@linux.com> > --- > target/riscv/insn32.decode | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/target/riscv/insn32.decode b/target/riscv/insn32.decode > index 5bbedc254c..d3f798ca10 100644 > --- a/target/riscv/insn32.decode > +++ b/target/riscv/insn32.decode > @@ -168,7 +168,7 @@ sraw 0100000 ..... ..... 101 ..... 0111011 @r > > # *** RV128I Base Instruction Set (in addition to RV64I) *** > ldu ............ ..... 111 ..... 0000011 @i > -lq ............ ..... 010 ..... 0001111 @i > +lq ............ ..... 111 ..... 0001111 @i > sq ............ ..... 100 ..... 0100011 @s > addid ............ ..... 000 ..... 1011011 @i > sllid 000000 ...... ..... 001 ..... 1011011 @sh6 -- +---------------------------------------------------------------------------+ | Frédéric Pétrot, Pr. Grenoble INP-Ensimag/TIMA, Ensimag deputy director | | Mob/Pho: +33 6 74 57 99 65/+33 4 76 57 48 70 Ad augusta per angusta | | http://tima.univ-grenoble-alpes.fr frederic.petrot@univ-grenoble-alpes.fr | +---------------------------------------------------------------------------+
Hi Frédéric, you are right, I misunderstood the "LQ is added to the MISC-MEM major opcode" part of the spec. I saw the encoding conflict with the CBO instructions and thought of a bug in qemu's LQ encoding. Philipp already highlighted that cbo.* instructions are actually LQ with rd=0. Thanks, Christoph On Wed, Jan 19, 2022 at 8:45 PM Frédéric Pétrot <frederic.petrot@univ-grenoble-alpes.fr> wrote: > > Le 18/01/2022 à 17:32, Christoph Muellner a écrit : > > If LQ has func3==010 and is located in the MISC-MEM opcodes, > > then it conflicts with the CBO opcode space. > > However, since LQ is specified as: "LQ is added to the MISC-MEM major > > opcode", we have an implementation bug, because 'major opcode' > > refers to func3, which must be 111. > > > > This results in the following instruction encodings: > > > > lq ........ ........ .111.... .0001111 > > cbo_clean 00000000 0001.... .0100000 00001111 > > cbo_flush 00000000 0010.... .0100000 00001111 > > cbo_inval 00000000 0000.... .0100000 00001111 > > cbo_zero 00000000 0100.... .0100000 00001111 > > ^^^-func3 > > ^^^^^^^-opcode > > Hello Christoph, > I see page table 26.1 of the last riscv-isa-manual.pdf what is called major > opcodes in my understanding, and MISC-MEM is one of them with value 00_111_11. > The value for func3 that I chose comes from > https://github.com/michaeljclark/riscv-meta/blob/master/opcodes > which admittedly is out-dated, but I don't see any particular value for > LQ/SQ in the new spec either (I mean, riscv-isa-manual.pdf, any pointer we > could refer to ?). > I have nothing against changing the opcode, but then we need to change > disas/riscv.c which also uses the previous opcode to dump instructions when > running with -d in_asm. > > Frédéric > > > > Signed-off-by: Christoph Muellner <cmuellner@linux.com> > > --- > > target/riscv/insn32.decode | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/target/riscv/insn32.decode b/target/riscv/insn32.decode > > index 5bbedc254c..d3f798ca10 100644 > > --- a/target/riscv/insn32.decode > > +++ b/target/riscv/insn32.decode > > @@ -168,7 +168,7 @@ sraw 0100000 ..... ..... 101 ..... 0111011 @r > > > > # *** RV128I Base Instruction Set (in addition to RV64I) *** > > ldu ............ ..... 111 ..... 0000011 @i > > -lq ............ ..... 010 ..... 0001111 @i > > +lq ............ ..... 111 ..... 0001111 @i > > sq ............ ..... 100 ..... 0100011 @s > > addid ............ ..... 000 ..... 1011011 @i > > sllid 000000 ...... ..... 001 ..... 1011011 @sh6 > > -- > +---------------------------------------------------------------------------+ > | Frédéric Pétrot, Pr. Grenoble INP-Ensimag/TIMA, Ensimag deputy director | > | Mob/Pho: +33 6 74 57 99 65/+33 4 76 57 48 70 Ad augusta per angusta | > | http://tima.univ-grenoble-alpes.fr frederic.petrot@univ-grenoble-alpes.fr | > +---------------------------------------------------------------------------+
The cbo.* mnemonics share their opcode space with lq for those cases where rd == 0 ("brownfield" encodings). "Major opcode" refers to inst[6:0] according to chapter 26. In overlapping multi-group syntax, this would look like: > { > > # *** RV32 Zicbom Standard Extension *** > > cbo_clean 0000000 00001 ..... 010 00000 0001111 @sfence_vm > > cbo_flush 0000000 00010 ..... 010 00000 0001111 @sfence_vm > > cbo_inval 0000000 00000 ..... 010 00000 0001111 @sfence_vm > > > # *** RV32 Zicboz Standard Extension *** > > cbo_zero 0000000 00100 ..... 010 00000 0001111 @sfence_vm > > > # *** RVI128 lq *** > > lq ............ ..... 010 ..... 0001111 @i > > } > Instead of using a multigroup here, I would recommend that you take a look at https://patchwork.kernel.org/project/qemu-devel/list/?series=605340 where we have added a table of optional decoders — this could be used to split these off into separate decoders that are run before the regular decoder, if & only if Zicboc and/or Zicboz are enabled. Cheers, Philipp. On Tue, 18 Jan 2022 at 17:32, Christoph Muellner <cmuellner@linux.com> wrote: > If LQ has func3==010 and is located in the MISC-MEM opcodes, > then it conflicts with the CBO opcode space. > However, since LQ is specified as: "LQ is added to the MISC-MEM major > opcode", we have an implementation bug, because 'major opcode' > refers to func3, which must be 111. > > This results in the following instruction encodings: > > lq ........ ........ .111.... .0001111 > cbo_clean 00000000 0001.... .0100000 00001111 > cbo_flush 00000000 0010.... .0100000 00001111 > cbo_inval 00000000 0000.... .0100000 00001111 > cbo_zero 00000000 0100.... .0100000 00001111 > ^^^-func3 > ^^^^^^^-opcode > > Signed-off-by: Christoph Muellner <cmuellner@linux.com> > --- > target/riscv/insn32.decode | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/target/riscv/insn32.decode b/target/riscv/insn32.decode > index 5bbedc254c..d3f798ca10 100644 > --- a/target/riscv/insn32.decode > +++ b/target/riscv/insn32.decode > @@ -168,7 +168,7 @@ sraw 0100000 ..... ..... 101 ..... 0111011 @r > > # *** RV128I Base Instruction Set (in addition to RV64I) *** > ldu ............ ..... 111 ..... 0000011 @i > -lq ............ ..... 010 ..... 0001111 @i > +lq ............ ..... 111 ..... 0001111 @i > sq ............ ..... 100 ..... 0100011 @s > addid ............ ..... 000 ..... 1011011 @i > sllid 000000 ...... ..... 001 ..... 1011011 @sh6 > -- > 2.34.1 > >
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