The cpuv4 added a new unconditional bswap instruction with following
behaviour:

BPF_ALU64 | BPF_TO_LE | BPF_END with imm = 16/32/64 means:
dst = bswap16(dst)
dst = bswap32(dst)
dst = bswap64(dst)

As we already support converting to big-endian from little-endian we can
use the same for unconditional bswap. just treat the unconditional scenario
the same as big-endian conversion.

Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
---
 arch/arm/net/bpf_jit_32.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
index 56ea8022e989..f837db5c71b1 100644
--- a/arch/arm/net/bpf_jit_32.c
+++ b/arch/arm/net/bpf_jit_32.c
@@ -1633,8 +1633,10 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx)
 	/* dst = htobe(dst) */
 	case BPF_ALU | BPF_END | BPF_FROM_LE:
 	case BPF_ALU | BPF_END | BPF_FROM_BE:
+	/* dst = bswap(dst) */
+	case BPF_ALU64 | BPF_END | BPF_TO_LE:
 		rd = arm_bpf_get_reg64(dst, tmp, ctx);
-		if (BPF_SRC(code) == BPF_FROM_LE)
+		if (BPF_SRC(code) == BPF_FROM_LE && BPF_CLASS(code) != BPF_ALU64)
 			goto emit_bswap_uxt;
 		switch (imm) {
 		case 16:
-- 
2.39.2

On Wed, Sep 06, 2023 at 06:33:16PM +0000, Puranjay Mohan wrote:
> @@ -1633,8 +1633,10 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx)
>  	/* dst = htobe(dst) */
>  	case BPF_ALU | BPF_END | BPF_FROM_LE:
>  	case BPF_ALU | BPF_END | BPF_FROM_BE:
> +	/* dst = bswap(dst) */
> +	case BPF_ALU64 | BPF_END | BPF_TO_LE:
>  		rd = arm_bpf_get_reg64(dst, tmp, ctx);
> -		if (BPF_SRC(code) == BPF_FROM_LE)
> +		if (BPF_SRC(code) == BPF_FROM_LE && BPF_CLASS(code) != BPF_ALU64)

With the addition of the BPF_ALU64 case, I'm wondering why this if() is
affected. If you were adding:

	case BPF_ALU64 | BPF_END | BPF_FROM_LE:

then maybe there would be a reason, but the BPF_ALU64 | BPF_END |
BPF_TO_LE case will never match even the original if() statement.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!

On Thu, Sep 07 2023, Russell King (Oracle) wrote:

> On Wed, Sep 06, 2023 at 06:33:16PM +0000, Puranjay Mohan wrote:
>> @@ -1633,8 +1633,10 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx)
>>  	/* dst = htobe(dst) */
>>  	case BPF_ALU | BPF_END | BPF_FROM_LE:
>>  	case BPF_ALU | BPF_END | BPF_FROM_BE:
>> +	/* dst = bswap(dst) */
>> +	case BPF_ALU64 | BPF_END | BPF_TO_LE:
>>  		rd = arm_bpf_get_reg64(dst, tmp, ctx);
>> -		if (BPF_SRC(code) == BPF_FROM_LE)
>> +		if (BPF_SRC(code) == BPF_FROM_LE && BPF_CLASS(code) != BPF_ALU64)
>
> With the addition of the BPF_ALU64 case, I'm wondering why this if() is
> affected. If you were adding:
>
> 	case BPF_ALU64 | BPF_END | BPF_FROM_LE:
>
> then maybe there would be a reason, but the BPF_ALU64 | BPF_END |
> BPF_TO_LE case will never match even the original if() statement.

The reason is that these mean the same thing.
from: include/uapi/linux/bpf.h

#define BPF_TO_LE	0x00	/* convert to little-endian */
#define BPF_TO_BE	0x08	/* convert to big-endian */
#define BPF_FROM_LE	BPF_TO_LE
#define BPF_FROM_BE	BPF_TO_BE

So, to not cause confusion and follow the earlier cases I can add:

case BPF_ALU64 | BPF_END | BPF_FROM_LE:

in the next version.


Thanks,
Puranjay

On Thu, Sep 07, 2023 at 09:08:46AM +0000, Puranjay Mohan wrote:
> On Thu, Sep 07 2023, Russell King (Oracle) wrote:
> 
> > On Wed, Sep 06, 2023 at 06:33:16PM +0000, Puranjay Mohan wrote:
> >> @@ -1633,8 +1633,10 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx)
> >>  	/* dst = htobe(dst) */
> >>  	case BPF_ALU | BPF_END | BPF_FROM_LE:
> >>  	case BPF_ALU | BPF_END | BPF_FROM_BE:
> >> +	/* dst = bswap(dst) */
> >> +	case BPF_ALU64 | BPF_END | BPF_TO_LE:
> >>  		rd = arm_bpf_get_reg64(dst, tmp, ctx);
> >> -		if (BPF_SRC(code) == BPF_FROM_LE)
> >> +		if (BPF_SRC(code) == BPF_FROM_LE && BPF_CLASS(code) != BPF_ALU64)
> >
> > With the addition of the BPF_ALU64 case, I'm wondering why this if() is
> > affected. If you were adding:
> >
> > 	case BPF_ALU64 | BPF_END | BPF_FROM_LE:
> >
> > then maybe there would be a reason, but the BPF_ALU64 | BPF_END |
> > BPF_TO_LE case will never match even the original if() statement.
> 
> The reason is that these mean the same thing.
> from: include/uapi/linux/bpf.h
> 
> #define BPF_TO_LE	0x00	/* convert to little-endian */
> #define BPF_TO_BE	0x08	/* convert to big-endian */
> #define BPF_FROM_LE	BPF_TO_LE
> #define BPF_FROM_BE	BPF_TO_BE
> 
> So, to not cause confusion and follow the earlier cases I can add:
> 
> case BPF_ALU64 | BPF_END | BPF_FROM_LE:
> 
> in the next version.

It might be worth adding a comment after each stating one of:

	/* also BPF_TO_LE */
	/* also BPF_TO_BE */

as appropriate to make this more readable.

Thanks.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!