[PATCH net] lib: packing: fix shift wrapping in bit_reverse()

[PATCH net] lib: packing: fix shift wrapping in bit_reverse()

[Dan Carpenter]

The bit_reverse() function is clearly supposed to be able to handle
64 bit values, but the types for "(1 << i)" and "bit << (width - i - 1)"
are not enough to handle more than 32 bits.

Fixes: 554aae35007e ("lib: Add support for generic packing operations")
Signed-off-by: Dan Carpenter <error27@gmail.com>
---
 lib/packing.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/lib/packing.c b/lib/packing.c
index 9a72f4bbf0e2..9d7418052f5a 100644
--- a/lib/packing.c
+++ b/lib/packing.c
@@ -32,12 +32,11 @@ static int get_reverse_lsw32_offset(int offset, size_t len)
 static u64 bit_reverse(u64 val, unsigned int width)
 {
 	u64 new_val = 0;
-	unsigned int bit;
 	unsigned int i;
 
 	for (i = 0; i < width; i++) {
-		bit = (val & (1 << i)) != 0;
-		new_val |= (bit << (width - i - 1));
+		if (val & BIT_ULL(1))
+			new_val |= BIT_ULL(width - i - 1);
 	}
 	return new_val;
 }
-- 
2.35.1

Re: [PATCH net] lib: packing: fix shift wrapping in bit_reverse()

[Vladimir Oltean]

On Wed, Dec 07, 2022 at 02:23:28PM +0300, Dan Carpenter wrote:
> The bit_reverse() function is clearly supposed to be able to handle
> 64 bit values, but the types for "(1 << i)" and "bit << (width - i - 1)"
> are not enough to handle more than 32 bits.
> 
> Fixes: 554aae35007e ("lib: Add support for generic packing operations")
> Signed-off-by: Dan Carpenter <error27@gmail.com>
> ---
>  lib/packing.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/packing.c b/lib/packing.c
> index 9a72f4bbf0e2..9d7418052f5a 100644
> --- a/lib/packing.c
> +++ b/lib/packing.c
> @@ -32,12 +32,11 @@ static int get_reverse_lsw32_offset(int offset, size_t len)
>  static u64 bit_reverse(u64 val, unsigned int width)
>  {
>  	u64 new_val = 0;
> -	unsigned int bit;
>  	unsigned int i;
>  
>  	for (i = 0; i < width; i++) {
> -		bit = (val & (1 << i)) != 0;
> -		new_val |= (bit << (width - i - 1));
> +		if (val & BIT_ULL(1))

hmm, why 1 and not i?

> +			new_val |= BIT_ULL(width - i - 1);
>  	}
>  	return new_val;
>  }
> -- 
> 2.35.1
> 

Re: [PATCH net] lib: packing: fix shift wrapping in bit_reverse()

[Dan Carpenter]

On Wed, Dec 07, 2022 at 02:19:36PM +0200, Vladimir Oltean wrote:
> On Wed, Dec 07, 2022 at 02:23:28PM +0300, Dan Carpenter wrote:
> > The bit_reverse() function is clearly supposed to be able to handle
> > 64 bit values, but the types for "(1 << i)" and "bit << (width - i - 1)"
> > are not enough to handle more than 32 bits.
> > 
> > Fixes: 554aae35007e ("lib: Add support for generic packing operations")
> > Signed-off-by: Dan Carpenter <error27@gmail.com>
> > ---
> >  lib/packing.c | 5 ++---
> >  1 file changed, 2 insertions(+), 3 deletions(-)
> > 
> > diff --git a/lib/packing.c b/lib/packing.c
> > index 9a72f4bbf0e2..9d7418052f5a 100644
> > --- a/lib/packing.c
> > +++ b/lib/packing.c
> > @@ -32,12 +32,11 @@ static int get_reverse_lsw32_offset(int offset, size_t len)
> >  static u64 bit_reverse(u64 val, unsigned int width)
> >  {
> >  	u64 new_val = 0;
> > -	unsigned int bit;
> >  	unsigned int i;
> >  
> >  	for (i = 0; i < width; i++) {
> > -		bit = (val & (1 << i)) != 0;
> > -		new_val |= (bit << (width - i - 1));
> > +		if (val & BIT_ULL(1))
> 
> hmm, why 1 and not i?

Because I'm a moron.  Let me resend.

regards,
dan carpenter

Re: [PATCH net] lib: packing: fix shift wrapping in bit_reverse()

[Vladimir Oltean]

On Wed, Dec 07, 2022 at 03:21:04PM +0300, Dan Carpenter wrote:
> On Wed, Dec 07, 2022 at 02:19:36PM +0200, Vladimir Oltean wrote:
> > On Wed, Dec 07, 2022 at 02:23:28PM +0300, Dan Carpenter wrote:
> > > The bit_reverse() function is clearly supposed to be able to handle
> > > 64 bit values, but the types for "(1 << i)" and "bit << (width - i - 1)"
> > > are not enough to handle more than 32 bits.
> > > 
> > > Fixes: 554aae35007e ("lib: Add support for generic packing operations")
> > > Signed-off-by: Dan Carpenter <error27@gmail.com>
> > > ---
> > >  lib/packing.c | 5 ++---
> > >  1 file changed, 2 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/lib/packing.c b/lib/packing.c
> > > index 9a72f4bbf0e2..9d7418052f5a 100644
> > > --- a/lib/packing.c
> > > +++ b/lib/packing.c
> > > @@ -32,12 +32,11 @@ static int get_reverse_lsw32_offset(int offset, size_t len)
> > >  static u64 bit_reverse(u64 val, unsigned int width)
> > >  {
> > >  	u64 new_val = 0;
> > > -	unsigned int bit;
> > >  	unsigned int i;
> > >  
> > >  	for (i = 0; i < width; i++) {
> > > -		bit = (val & (1 << i)) != 0;
> > > -		new_val |= (bit << (width - i - 1));
> > > +		if (val & BIT_ULL(1))
> > 
> > hmm, why 1 and not i?
> 
> Because I'm a moron.  Let me resend.

Wait a second, I deliberately wrote the code without conditionals.
Let me look at the code disassembly before and after the patch and see
what they look like.

Re: [PATCH net] lib: packing: fix shift wrapping in bit_reverse()

[Dan Carpenter]

On Wed, Dec 07, 2022 at 02:22:54PM +0200, Vladimir Oltean wrote:
> On Wed, Dec 07, 2022 at 03:21:04PM +0300, Dan Carpenter wrote:
> > On Wed, Dec 07, 2022 at 02:19:36PM +0200, Vladimir Oltean wrote:
> > > On Wed, Dec 07, 2022 at 02:23:28PM +0300, Dan Carpenter wrote:
> > > > The bit_reverse() function is clearly supposed to be able to handle
> > > > 64 bit values, but the types for "(1 << i)" and "bit << (width - i - 1)"
> > > > are not enough to handle more than 32 bits.
> > > > 
> > > > Fixes: 554aae35007e ("lib: Add support for generic packing operations")
> > > > Signed-off-by: Dan Carpenter <error27@gmail.com>
> > > > ---
> > > >  lib/packing.c | 5 ++---
> > > >  1 file changed, 2 insertions(+), 3 deletions(-)
> > > > 
> > > > diff --git a/lib/packing.c b/lib/packing.c
> > > > index 9a72f4bbf0e2..9d7418052f5a 100644
> > > > --- a/lib/packing.c
> > > > +++ b/lib/packing.c
> > > > @@ -32,12 +32,11 @@ static int get_reverse_lsw32_offset(int offset, size_t len)
> > > >  static u64 bit_reverse(u64 val, unsigned int width)
> > > >  {
> > > >  	u64 new_val = 0;
> > > > -	unsigned int bit;
> > > >  	unsigned int i;
> > > >  
> > > >  	for (i = 0; i < width; i++) {
> > > > -		bit = (val & (1 << i)) != 0;
> > > > -		new_val |= (bit << (width - i - 1));
> > > > +		if (val & BIT_ULL(1))
> > > 
> > > hmm, why 1 and not i?
> > 
> > Because I'm a moron.  Let me resend.
> 
> Wait a second, I deliberately wrote the code without conditionals.
> Let me look at the code disassembly before and after the patch and see
> what they look like.

My crappy benchmark says that the if statement is faster.  22 vs 26
seconds.

regards,
dan carpenter

#include <stdio.h>
#include <limits.h>
#include <stdbool.h>
#include <string.h>

#define BIT(n) (1 << (n))
#define BIT_ULL(n) (1ULL << (n))

#define u64 unsigned long long
#define u32 unsigned int
#define u16 unsigned short
#define u8  unsigned char

static u64 bit_reverse1(u64 val, unsigned int width)
{
	u64 new_val = 0;
	unsigned int i;

	for (i = 0; i < width; i++) {
		if (val & BIT_ULL(i))
			new_val |= BIT_ULL(width - i - 1);
	}
	return new_val;
}

static u64 bit_reverse2(u64 val, unsigned int width)
{
	u64 new_val = 0;
	u64 bit;
	unsigned int i;

	for (i = 0; i < width; i++) {
		bit = (val & BIT_ULL(i)) != 0;
		new_val |= (bit << (width - i - 1));
	}
	return new_val;
}

int main(void)
{
	unsigned long long val;

	for (val = ULLONG_MAX - INT_MAX; val; val++)
		bit_reverse1(val, 2);

	return 0;
}

Re: [PATCH net] lib: packing: fix shift wrapping in bit_reverse()

[Vladimir Oltean]

On Wed, Dec 07, 2022 at 02:22:54PM +0200, Vladimir Oltean wrote:
> Wait a second, I deliberately wrote the code without conditionals.
> Let me look at the code disassembly before and after the patch and see
> what they look like.

Before (make lib/packing.lst on arm64):

	for (i = 0; i < width; i++) {
  1c:	310004ec 	adds	w12, w7, #0x1
  20:	540001c0 	b.eq	58 <adjust_for_msb_right_quirk+0x58>  // b.none
  24:	52800004 	mov	w4, #0x0                   	// #0
		bit = (val & (1 << i)) != 0;
  28:	5280002b 	mov	w11, #0x1                   	// #1
  2c:	d503201f 	nop
  30:	1ac42166 	lsl	w6, w11, w4
		new_val |= (bit << (width - i - 1));
  34:	4b0400e9 	sub	w9, w7, w4
		bit = (val & (1 << i)) != 0;
  38:	93407cc6 	sxtw	x6, w6		/* We don't want sign extension */
  3c:	ea0a00df 	tst	x6, x10
  40:	1a9f07e6 	cset	w6, ne  // ne = any
	for (i = 0; i < width; i++) {
  44:	6b07009f 	cmp	w4, w7
  48:	11000484 	add	w4, w4, #0x1
		new_val |= (bit << (width - i - 1));
  4c:	1ac920c6 	lsl	w6, w6, w9
  50:	aa060108 	orr	x8, x8, x6
	for (i = 0; i < width; i++) {
  54:	54fffee1 	b.ne	30 <adjust_for_msb_right_quirk+0x30>  // b.any


Then this modified code:

static u64 bit_reverse(u64 val, unsigned int width)
{
	u64 new_val = 0;
	unsigned int i;

	for (i = 0; i < width; i++)
		if (val & BIT_ULL(i))
			new_val |= BIT_ULL(width - i - 1);

	return new_val;
}

compiles to this:

	for (i = 0; i < width; i++) {
  1c:	310004eb 	adds	w11, w7, #0x1
  20:	540001c0 	b.eq	58 <adjust_for_msb_right_quirk+0x58>  // b.none
  24:	52800005 	mov	w5, #0x0                   	// #0
			new_val |= BIT_ULL(width - i - 1);
  28:	d280002a 	mov	x10, #0x1                   	// #1
  2c:	14000002 	b	34 <adjust_for_msb_right_quirk+0x34>	/* this is an unconditional jump to "sub w4, w7, w5", skipping the assignment to w5 */
  30:	2a0803e5 	mov	w5, w8			/* this is only hit by the backwards jump b.ne 30 at the end */
  34:	4b0500e4 	sub	w4, w7, w5
		if (val & BIT_ULL(i))
  38:	9ac52528 	lsr	x8, x9, x5
			new_val |= BIT_ULL(width - i - 1);
  3c:	f240011f 	tst	x8, #0x1
	for (i = 0; i < width; i++) {
  40:	110004a8 	add	w8, w5, #0x1
			new_val |= BIT_ULL(width - i - 1);
  44:	9ac42144 	lsl	x4, x10, x4
  48:	aa0400c4 	orr	x4, x6, x4
  4c:	9a861086 	csel	x6, x4, x6, ne  // ne = any
	for (i = 0; i < width; i++) {
  50:	6b0700bf 	cmp	w5, w7
  54:	54fffee1 	b.ne	30 <adjust_for_msb_right_quirk+0x30>  // b.any

which indeed has no branch in the main loop (between 0x30 and 0x54),
because as I explained, the "b 34" doesn't count - it's not in the loop.

Additionally, this rewritten code which is considerably more obscure in C:

static u64 bit_reverse(u64 val, unsigned int width)
{
	u64 new_val = 0;
	unsigned int i;

	for (i = 0; i < width; i++)
		new_val |= !!(val & BIT_ULL(i)) ?
			   BIT_ULL(width - i - 1) : 0;

	return new_val;
}

compiles to the exact same assembly code as the variant with "if":

	for (i = 0; i < width; i++)
  1c:	310004eb 	adds	w11, w7, #0x1
  20:	540001c0 	b.eq	58 <adjust_for_msb_right_quirk+0x58>  // b.none
  24:	52800005 	mov	w5, #0x0                   	// #0
		new_val |= !!(val & BIT_ULL(i)) ?
  28:	d280002a 	mov	x10, #0x1                   	// #1
  2c:	14000002 	b	34 <adjust_for_msb_right_quirk+0x34>
  30:	2a0803e5 	mov	w5, w8
  34:	4b0500e4 	sub	w4, w7, w5
  38:	9ac52528 	lsr	x8, x9, x5
  3c:	f240011f 	tst	x8, #0x1
	for (i = 0; i < width; i++)
  40:	110004a8 	add	w8, w5, #0x1
		new_val |= !!(val & BIT_ULL(i)) ?
  44:	9ac42144 	lsl	x4, x10, x4
  48:	aa0400c4 	orr	x4, x6, x4
  4c:	9a861086 	csel	x6, x4, x6, ne  // ne = any
	for (i = 0; i < width; i++)
  50:	6b0700bf 	cmp	w5, w7
  54:	54fffee1 	b.ne	30 <adjust_for_msb_right_quirk+0x30>  // b.any

So this is good with the "if".

Re: [PATCH net] lib: packing: fix shift wrapping in bit_reverse()

[Vladimir Oltean]

On Wed, Dec 07, 2022 at 03:51:08PM +0300, Dan Carpenter wrote:
> My crappy benchmark says that the if statement is faster.  22 vs 26
> seconds.

Sure that's not just noise in the measurements? :)

RE: [PATCH net] lib: packing: fix shift wrapping in bit_reverse()

[David Laight]

From: Dan Carpenter
> Sent: 07 December 2022 12:21
....
> > > -		new_val |= (bit << (width - i - 1));
> > > +		if (val & BIT_ULL(1))
> >
> > hmm, why 1 and not i?
> 
> Because I'm a moron.  Let me resend.

Since we're not writing FORTRAN-IV why not use a variable
name that is harder to confuse with 1?

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

Re: [PATCH net] lib: packing: fix shift wrapping in bit_reverse()

[Vladimir Oltean]

On Wed, Dec 07, 2022 at 07:41:28PM +0000, David Laight wrote:
> From: Dan Carpenter
> > Sent: 07 December 2022 12:21
> ....
> > > > -		new_val |= (bit << (width - i - 1));
> > > > +		if (val & BIT_ULL(1))
> > >
> > > hmm, why 1 and not i?
> > 
> > Because I'm a moron.  Let me resend.
> 
> Since we're not writing FORTRAN-IV why not use a variable
> name that is harder to confuse with 1?

How about 'k'?

Re: [PATCH net] lib: packing: fix shift wrapping in bit_reverse()

[Uladzislau Koshchanka]

On Wed, 7 Dec 2022 at 14:30, Dan Carpenter <error27@gmail.com> wrote:
>
> The bit_reverse() function is clearly supposed to be able to handle
> 64 bit values, but the types for "(1 << i)" and "bit << (width - i - 1)"
> are not enough to handle more than 32 bits.

It seems from the surrounding code that this function is only called
for width of up to a byte (but correct me if I'm wrong). There are
fast implementations of bit-reverse in include/linux/bitrev.h. It's
better to just remove this function entirely and call bitrev8, which
is just a precalc-table lookup. While at it, also sort includes.

Signed-off-by: Uladzislau Koshchanka <koshchanka@gmail.com>

 lib/packing.c | 20 ++++----------------
 1 file changed, 4 insertions(+), 16 deletions(-)

diff --git a/lib/packing.c b/lib/packing.c
index 9a72f4bbf0e2..47ea47c1198a 100644
--- a/lib/packing.c
+++ b/lib/packing.c
@@ -2,10 +2,11 @@
 /* Copyright 2016-2018 NXP
  * Copyright (c) 2018-2019, Vladimir Oltean <olteanv@gmail.com>
  */
-#include <linux/packing.h>
-#include <linux/module.h>
 #include <linux/bitops.h>
+#include <linux/bitrev.h>
 #include <linux/errno.h>
+#include <linux/module.h>
+#include <linux/packing.h>
 #include <linux/types.h>

 static int get_le_offset(int offset)
@@ -29,19 +30,6 @@ static int get_reverse_lsw32_offset(int offset, size_t len)
        return word_index * 4 + offset;
 }

-static u64 bit_reverse(u64 val, unsigned int width)
-{
-       u64 new_val = 0;
-       unsigned int bit;
-       unsigned int i;
-
-       for (i = 0; i < width; i++) {
-               bit = (val & (1 << i)) != 0;
-               new_val |= (bit << (width - i - 1));
-       }
-       return new_val;
-}
-
 static void adjust_for_msb_right_quirk(u64 *to_write, int *box_start_bit,
                                       int *box_end_bit, u8 *box_mask)
 {
@@ -49,7 +37,7 @@ static void adjust_for_msb_right_quirk(u64
*to_write, int *box_start_bit,
        int new_box_start_bit, new_box_end_bit;

        *to_write >>= *box_end_bit;
-       *to_write = bit_reverse(*to_write, box_bit_width);
+       *to_write = bitrev8(*to_write) >> (8 - box_bit_width);
        *to_write <<= *box_end_bit;

        new_box_end_bit   = box_bit_width - *box_start_bit - 1;

Re: [PATCH net] lib: packing: fix shift wrapping in bit_reverse()

[Vladimir Oltean]

Hi Uladzislau,

On Fri, Dec 09, 2022 at 11:21:21AM +0300, Uladzislau Koshchanka wrote:
> On Wed, 7 Dec 2022 at 14:30, Dan Carpenter <error27@gmail.com> wrote:
> >
> > The bit_reverse() function is clearly supposed to be able to handle
> > 64 bit values, but the types for "(1 << i)" and "bit << (width - i - 1)"
> > are not enough to handle more than 32 bits.
> 
> It seems from the surrounding code that this function is only called
> for width of up to a byte (but correct me if I'm wrong).

This observation is quite true. I was quite lazy to look and remember
whether this is the case, but the comment says it quite clearly:

		/* Bit indices into the currently accessed 8-bit box */
		int box_start_bit, box_end_bit, box_addr;

> There are fast implementations of bit-reverse in include/linux/bitrev.h.
> It's better to just remove this function entirely and call bitrev8,
> which is just a precalc-table lookup. While at it, also sort includes.

The problem I see with bitrev8 is that the byte_rev_table[] can
seemingly be built as a module (the BITREVERSE Kconfig knob is tristate,
and btw your patch doesn't make PACKING select BITREVERSE). But PACKING
is bool. IIRC, I got comments during review that it's not worth making
packing a module, but I may remember wrong.

> @@ -49,7 +37,7 @@ static void adjust_for_msb_right_quirk(u64
> *to_write, int *box_start_bit,
>         int new_box_start_bit, new_box_end_bit;
> 
>         *to_write >>= *box_end_bit;
> -       *to_write = bit_reverse(*to_write, box_bit_width);
> +       *to_write = bitrev8(*to_write) >> (8 - box_bit_width);
>         *to_write <<= *box_end_bit;
> 
>         new_box_end_bit   = box_bit_width - *box_start_bit - 1;

Anyway, the patch works in principle. I know this because I wrote the
following patch to check:

From 17099a86291713d2bcf8137473daea5f390a2ef4 Mon Sep 17 00:00:00 2001
From: Vladimir Oltean <vladimir.oltean@nxp.com>
Date: Fri, 9 Dec 2022 16:23:35 +0200
Subject: [PATCH] lib: packing: add boot-time selftests

In case people want to make changes to the packing() implementation but
they aren't sure it's going to keep working, provide 16 boot-time calls
to packing() which exercise all combinations of quirks plus PACK |
UNPACK.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
 lib/Kconfig   |   9 +++
 lib/packing.c | 186 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 195 insertions(+)

diff --git a/lib/Kconfig b/lib/Kconfig
index 9bbf8a4b2108..54b8deaf44fc 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -39,6 +39,15 @@ config PACKING
 
 	  When in doubt, say N.
 
+config PACKING_SELFTESTS
+	bool "Selftests for packing library"
+	depends on PACKING
+	help
+	  Boot-time selftests to make sure that the packing and unpacking
+	  functions work properly.
+
+	  When in doubt, say N.
+
 config BITREVERSE
 	tristate
 
diff --git a/lib/packing.c b/lib/packing.c
index 9a72f4bbf0e2..aff70853b0c4 100644
--- a/lib/packing.c
+++ b/lib/packing.c
@@ -210,5 +210,191 @@ int packing(void *pbuf, u64 *uval, int startbit, int endbit, size_t pbuflen,
 }
 EXPORT_SYMBOL(packing);
 
+#if IS_ENABLED(CONFIG_PACKING_SELFTESTS)
+
+#define PBUF_LEN 16
+
+/* These selftests pack and unpack a magic 64-bit value (0xcafedeadbeefcafe) at
+ * a fixed logical offset (32) within an otherwise zero array of 128 bits
+ * (16 bytes). They test all possible bit layouts of the 128 bit buffer.
+ */
+static bool test_pack(u8 expected_pbuf[PBUF_LEN], u8 quirks)
+{
+	u64 uval = 0xcafedeadbeefcafe;
+	u8 pbuf[PBUF_LEN];
+	int err, i;
+
+	memset(pbuf, 0, PBUF_LEN);
+	err = packing(pbuf, &uval, 95, 32, PBUF_LEN, PACK, quirks);
+	if (err) {
+		pr_err("packing() returned %pe\n", ERR_PTR(err));
+		return false;
+	}
+
+	for (i = 0; i < PBUF_LEN; i++) {
+		if (pbuf[i] != expected_pbuf[i]) {
+			print_hex_dump(KERN_ERR, "pbuf:     ", DUMP_PREFIX_NONE,
+				       16, 1, pbuf, PBUF_LEN, false);
+			print_hex_dump(KERN_ERR, "expected: ", DUMP_PREFIX_NONE,
+				       16, 1, expected_pbuf, PBUF_LEN, false);
+			return false;
+		}
+	}
+
+	return true;
+}
+
+static bool test_unpack(u8 pbuf[PBUF_LEN], u8 quirks)
+{
+	u64 uval, expected_uval = 0xcafedeadbeefcafe;
+	int err;
+
+	err = packing(pbuf, &uval, 95, 32, PBUF_LEN, UNPACK, quirks);
+	if (err) {
+		pr_err("packing() returned %pe\n", ERR_PTR(err));
+		return false;
+	}
+
+	if (uval != expected_uval) {
+		pr_err("uval: 0x%llx expected 0x%llx\n", uval, expected_uval);
+		return false;
+	}
+
+	return true;
+}
+
+static void test_no_quirks(void)
+{
+	u8 pbuf[PBUF_LEN] = {0x00, 0x00, 0x00, 0x00, 0xca, 0xfe, 0xde, 0xad,
+			     0xbe, 0xef, 0xca, 0xfe, 0x00, 0x00, 0x00, 0x00};
+	bool ret;
+
+	ret = test_pack(pbuf, 0);
+	pr_info("packing with no quirks: %s\n", ret ? "OK" : "FAIL");
+
+	ret = test_unpack(pbuf, 0);
+	pr_info("unpacking with no quirks: %s\n", ret ? "OK" : "FAIL");
+}
+
+static void test_msb_right(void)
+{
+	u8 pbuf[PBUF_LEN] = {0x00, 0x00, 0x00, 0x00, 0x53, 0x7f, 0x7b, 0xb5,
+			     0x7d, 0xf7, 0x53, 0x7f, 0x00, 0x00, 0x00, 0x00};
+	bool ret;
+
+	ret = test_pack(pbuf, QUIRK_MSB_ON_THE_RIGHT);
+	pr_info("packing with QUIRK_MSB_ON_THE_RIGHT: %s\n",
+		ret ? "OK" : "FAIL");
+
+	ret = test_unpack(pbuf, QUIRK_MSB_ON_THE_RIGHT);
+	pr_info("unpacking with QUIRK_MSB_ON_THE_RIGHT: %s\n",
+		ret ? "OK" : "FAIL");
+}
+
+static void test_le(void)
+{
+	u8 pbuf[PBUF_LEN] = {0x00, 0x00, 0x00, 0x00, 0xad, 0xde, 0xfe, 0xca,
+			     0xfe, 0xca, 0xef, 0xbe, 0x00, 0x00, 0x00, 0x00};
+	bool ret;
+
+	ret = test_pack(pbuf, QUIRK_LITTLE_ENDIAN);
+	pr_info("packing with QUIRK_LITTLE_ENDIAN: %s\n", ret ? "OK" : "FAIL");
+
+	ret = test_unpack(pbuf, QUIRK_LITTLE_ENDIAN);
+	pr_info("unpacking with QUIRK_LITTLE_ENDIAN: %s\n",
+		ret ? "OK" : "FAIL");
+}
+
+static void test_le_msb_right(void)
+{
+	u8 pbuf[PBUF_LEN] = {0x00, 0x00, 0x00, 0x00, 0xb5, 0x7b, 0x7f, 0x53,
+			     0x7f, 0x53, 0xf7, 0x7d, 0x00, 0x00, 0x00, 0x00};
+	bool ret;
+
+	ret = test_pack(pbuf, QUIRK_LITTLE_ENDIAN | QUIRK_MSB_ON_THE_RIGHT);
+	pr_info("packing with QUIRK_LITTLE_ENDIAN | QUIRK_MSB_ON_THE_RIGHT: %s\n",
+		ret ? "OK" : "FAIL");
+
+	ret = test_unpack(pbuf, QUIRK_LITTLE_ENDIAN | QUIRK_MSB_ON_THE_RIGHT);
+	pr_info("unpacking with QUIRK_LITTLE_ENDIAN | QUIRK_MSB_ON_THE_RIGHT: %s\n",
+		ret ? "OK" : "FAIL");
+}
+
+static void test_lsw32_first(void)
+{
+	u8 pbuf[PBUF_LEN] = {0x00, 0x00, 0x00, 0x00, 0xbe, 0xef, 0xca, 0xfe,
+			     0xca, 0xfe, 0xde, 0xad, 0x00, 0x00, 0x00, 0x00};
+	bool ret;
+
+	ret = test_pack(pbuf, QUIRK_LSW32_IS_FIRST);
+	pr_info("packing with QUIRK_LSW32_IS_FIRST: %s\n", ret ? "OK" : "FAIL");
+
+	ret = test_unpack(pbuf, QUIRK_LSW32_IS_FIRST);
+	pr_info("unpacking with QUIRK_LSW32_IS_FIRST: %s\n", ret ? "OK" : "FAIL");
+}
+
+static void test_lsw32_first_msb_right(void)
+{
+	u8 pbuf[PBUF_LEN] = {0x00, 0x00, 0x00, 0x00, 0x7d, 0xf7, 0x53, 0x7f,
+			     0x53, 0x7f, 0x7b, 0xb5, 0x00, 0x00, 0x00, 0x00};
+	bool ret;
+
+	ret = test_pack(pbuf, QUIRK_LSW32_IS_FIRST | QUIRK_MSB_ON_THE_RIGHT);
+	pr_info("packing with QUIRK_LSW32_IS_FIRST | QUIRK_MSB_ON_THE_RIGHT: %s\n",
+		ret ? "OK" : "FAIL");
+
+	ret = test_unpack(pbuf, QUIRK_LSW32_IS_FIRST | QUIRK_MSB_ON_THE_RIGHT);
+	pr_info("unpacking with QUIRK_LSW32_IS_FIRST | QUIRK_MSB_ON_THE_RIGHT: %s\n",
+		ret ? "OK" : "FAIL");
+}
+
+static void test_lsw32_first_le(void)
+{
+	u8 pbuf[PBUF_LEN] = {0x00, 0x00, 0x00, 0x00, 0xfe, 0xca, 0xef, 0xbe,
+			     0xad, 0xde, 0xfe, 0xca, 0x00, 0x00, 0x00, 0x00};
+	bool ret;
+
+	ret = test_pack(pbuf, QUIRK_LSW32_IS_FIRST | QUIRK_LITTLE_ENDIAN);
+	pr_info("packing with QUIRK_LSW32_IS_FIRST | QUIRK_LITTLE_ENDIAN: %s\n",
+		ret ? "OK" : "FAIL");
+
+	ret = test_unpack(pbuf, QUIRK_LSW32_IS_FIRST | QUIRK_LITTLE_ENDIAN);
+	pr_info("unpacking with QUIRK_LSW32_IS_FIRST | QUIRK_LITTLE_ENDIAN: %s\n",
+		ret ? "OK" : "FAIL");
+}
+
+static void test_lsw32_first_le_msb_right(void)
+{
+	u8 pbuf[PBUF_LEN] = {0x00, 0x00, 0x00, 0x00, 0x7f, 0x53, 0xf7, 0x7d,
+			     0xb5, 0x7b, 0x7f, 0x53, 0x00, 0x00, 0x00, 0x00};
+	bool ret;
+
+	ret = test_pack(pbuf, QUIRK_LSW32_IS_FIRST | QUIRK_LITTLE_ENDIAN |
+			QUIRK_MSB_ON_THE_RIGHT);
+	pr_info("packing with QUIRK_LSW32_IS_FIRST | QUIRK_LITTLE_ENDIAN | QUIRK_MSB_ON_THE_RIGHT: %s\n",
+		ret ? "OK" : "FAIL");
+
+	ret = test_unpack(pbuf, QUIRK_LSW32_IS_FIRST | QUIRK_LITTLE_ENDIAN |
+			  QUIRK_MSB_ON_THE_RIGHT);
+	pr_info("unpacking with QUIRK_LSW32_IS_FIRST | QUIRK_LITTLE_ENDIAN | QUIRK_MSB_ON_THE_RIGHT: %s\n",
+		ret ? "OK" : "FAIL");
+}
+
+static int __init packing_init(void)
+{
+	test_no_quirks();
+	test_msb_right();
+	test_le();
+	test_le_msb_right();
+	test_lsw32_first();
+	test_lsw32_first_msb_right();
+	test_lsw32_first_le();
+	test_lsw32_first_le_msb_right();
+
+	return 0;
+}
+module_init(packing_init);
+#endif
+
 MODULE_LICENSE("GPL v2");
 MODULE_DESCRIPTION("Generic bitfield packing and unpacking");
-- 
2.34.1


I've been meaning to do this for a while, but I'm not sure what is the
best way to integrate such a thing. Does anyone have any idea?

Re: [PATCH net] lib: packing: fix shift wrapping in bit_reverse()

[Uladzislau Koshchanka]

Hi Vladimir,

> The problem I see with bitrev8 is that the byte_rev_table[] can
> seemingly be built as a module (the BITREVERSE Kconfig knob is tristate,
> and btw your patch doesn't make PACKING select BITREVERSE). But PACKING
> is bool. IIRC, I got comments during review that it's not worth making
> packing a module, but I may remember wrong.

Do you really think it's a problem? I personally would just select
BITREVERSE with/without making PACKING tristate. BITREVERSE is already
selected by CRC32 which defaults to y, so just adding a select isn't a
change in the default. Can't think of a practical point in avoiding
linking against 256 bytes here.

In any case, it just doesn't look right to have multiple bit-reverse
implementations only because of Kconfig relations.

Re: [PATCH net] lib: packing: fix shift wrapping in bit_reverse()

[Vladimir Oltean]

On Sat, Dec 10, 2022 at 12:01:28AM +0300, Uladzislau Koshchanka wrote:
> Hi Vladimir,
> 
> > The problem I see with bitrev8 is that the byte_rev_table[] can
> > seemingly be built as a module (the BITREVERSE Kconfig knob is tristate,
> > and btw your patch doesn't make PACKING select BITREVERSE). But PACKING
> > is bool. IIRC, I got comments during review that it's not worth making
> > packing a module, but I may remember wrong.
> 
> Do you really think it's a problem? I personally would just select
> BITREVERSE with/without making PACKING tristate. BITREVERSE is already
> selected by CRC32 which defaults to y, so just adding a select isn't a
> change in the default. Can't think of a practical point in avoiding
> linking against 256 bytes here.
> 
> In any case, it just doesn't look right to have multiple bit-reverse
> implementations only because of Kconfig relations.

Ok, let's use BITREVERSE then. Could you submit your patch formally please?

Re: [PATCH net] lib: packing: fix shift wrapping in bit_reverse()

[Vladimir Oltean]

On Sat, Dec 10, 2022 at 12:06:51AM +0200, Vladimir Oltean wrote:
> On Sat, Dec 10, 2022 at 12:01:28AM +0300, Uladzislau Koshchanka wrote:
> > Hi Vladimir,
> > 
> > > The problem I see with bitrev8 is that the byte_rev_table[] can
> > > seemingly be built as a module (the BITREVERSE Kconfig knob is tristate,
> > > and btw your patch doesn't make PACKING select BITREVERSE). But PACKING
> > > is bool. IIRC, I got comments during review that it's not worth making
> > > packing a module, but I may remember wrong.
> > 
> > Do you really think it's a problem? I personally would just select
> > BITREVERSE with/without making PACKING tristate. BITREVERSE is already
> > selected by CRC32 which defaults to y, so just adding a select isn't a
> > change in the default. Can't think of a practical point in avoiding
> > linking against 256 bytes here.
> > 
> > In any case, it just doesn't look right to have multiple bit-reverse
> > implementations only because of Kconfig relations.
> 
> Ok, let's use BITREVERSE then. Could you submit your patch formally please?

Also, none of that 'while at it, do XYZ unrelated stuff'. One patch per
logical change please.

[PATCH] lib: packing: replace bit_reverse() with bitrev8()

[Uladzislau Koshchanka]

Remove bit_reverse() function.  Instead use bitrev8() from linux/bitrev.h +
bitshift.  Reduces code-repetition.

Signed-off-by: Uladzislau Koshchanka <koshchanka@gmail.com>
---
 lib/Kconfig   |  1 +
 lib/packing.c | 16 ++--------------
 2 files changed, 3 insertions(+), 14 deletions(-)

diff --git a/lib/Kconfig b/lib/Kconfig
index 9bbf8a4b2108..cc969ef58a2a 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -24,6 +24,7 @@ config LINEAR_RANGES
 
 config PACKING
 	bool "Generic bitfield packing and unpacking"
+	select BITREVERSE
 	default n
 	help
 	  This option provides the packing() helper function, which permits
diff --git a/lib/packing.c b/lib/packing.c
index 9a72f4bbf0e2..a96169237ae6 100644
--- a/lib/packing.c
+++ b/lib/packing.c
@@ -7,6 +7,7 @@
 #include <linux/bitops.h>
 #include <linux/errno.h>
 #include <linux/types.h>
+#include <linux/bitrev.h>
 
 static int get_le_offset(int offset)
 {
@@ -29,19 +30,6 @@ static int get_reverse_lsw32_offset(int offset, size_t len)
 	return word_index * 4 + offset;
 }
 
-static u64 bit_reverse(u64 val, unsigned int width)
-{
-	u64 new_val = 0;
-	unsigned int bit;
-	unsigned int i;
-
-	for (i = 0; i < width; i++) {
-		bit = (val & (1 << i)) != 0;
-		new_val |= (bit << (width - i - 1));
-	}
-	return new_val;
-}
-
 static void adjust_for_msb_right_quirk(u64 *to_write, int *box_start_bit,
 				       int *box_end_bit, u8 *box_mask)
 {
@@ -49,7 +37,7 @@ static void adjust_for_msb_right_quirk(u64 *to_write, int *box_start_bit,
 	int new_box_start_bit, new_box_end_bit;
 
 	*to_write >>= *box_end_bit;
-	*to_write = bit_reverse(*to_write, box_bit_width);
+	*to_write = bitrev8(*to_write) >> (8 - box_bit_width);
 	*to_write <<= *box_end_bit;
 
 	new_box_end_bit   = box_bit_width - *box_start_bit - 1;
-- 
2.34.1

Re: [PATCH] lib: packing: replace bit_reverse() with bitrev8()

[Vladimir Oltean]

On Sat, 10 Dec 2022 at 02:47, Uladzislau Koshchanka
<koshchanka@gmail.com> wrote:
>
> Remove bit_reverse() function.  Instead use bitrev8() from linux/bitrev.h +
> bitshift.  Reduces code-repetition.
>
> Signed-off-by: Uladzislau Koshchanka <koshchanka@gmail.com>
> ---

Reviewed-by: Vladimir Oltean <olteanv@gmail.com>

Re: [PATCH] lib: packing: replace bit_reverse() with bitrev8()

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (master)
by Jakub Kicinski <kuba@kernel.org>:

On Sat, 10 Dec 2022 03:44:23 +0300 you wrote:
> Remove bit_reverse() function.  Instead use bitrev8() from linux/bitrev.h +
> bitshift.  Reduces code-repetition.
> 
> Signed-off-by: Uladzislau Koshchanka <koshchanka@gmail.com>
> ---
>  lib/Kconfig   |  1 +
>  lib/packing.c | 16 ++--------------
>  2 files changed, 3 insertions(+), 14 deletions(-)

Here is the summary with links:
  - lib: packing: replace bit_reverse() with bitrev8()
    https://git.kernel.org/netdev/net-next/c/1280d4b76f34

You are awesome, thank you!
-- 
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