To avoid the compilation error below, it is needed to update to places
in common/page_alloc.c where flsl() is used as now flsl() returns unsigned int:

./include/xen/kernel.h:18:21: error: comparison of distinct pointer types lacks a cast [-Werror]
       18 |         (void) (&_x == &_y);            \
          |                     ^~
    common/page_alloc.c:1843:34: note: in expansion of macro 'min'
     1843 |         unsigned int inc_order = min(MAX_ORDER, flsl(e - s) - 1);

generic_fls{l} was used instead of __builtin_clz{l}(x) as if x is 0,
the result in undefined.

The prototype of the per-architecture fls{l}() functions was changed to
return 'unsigned int' to align with the generic implementation of these
functions and avoid introducing signed/unsigned mismatches.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
---
 The patch is almost independent from Andrew's patch series
 ( https://lore.kernel.org/xen-devel/20240313172716.2325427-1-andrew.cooper3@citrix.com/T/#t)
 except test_fls() function which IMO can be merged as a separate patch after Andrew's patch
 will be fully ready.
---
Changes in V10:
 - update return type of arch_flsl() across arcitectures to 'unsigned int' to be aligned
   with return type of generic flsl() in xen/bitops.h.
 - switch inline to always_inline for arch_flsl() across architectures to be in sync
   with other similar changes.
 - define arch_flsl as arch_fls not just only fls.
 - update the commit message ( add information that per-arch fls{l)() protypes were
   changed ).
---
Changes in V9:
 - update return type of fls and flsl() to unsigned int to be aligned with other
   bit ops.
 - update places where return value of fls() and flsl() is compared with int.
 - update the commit message.
---
Changes in V8:
 - do proper rebase: back definition of fls{l} to the current patch.
 - drop the changes which removed ffz() in PPC. it should be done not
   in this patch.
 - add a message after Signed-off.
---
Changes in V7:
 - Code style fixes
---
Changes in V6:
 - new patch for the patch series.
---
 xen/arch/arm/include/asm/arm32/bitops.h |  2 +-
 xen/arch/arm/include/asm/arm64/bitops.h |  6 ++----
 xen/arch/arm/include/asm/bitops.h       |  9 +++------
 xen/arch/ppc/include/asm/bitops.h       |  3 ---
 xen/arch/x86/include/asm/bitops.h       | 12 +++++++-----
 xen/common/bitops.c                     | 22 ++++++++++++++++++++++
 xen/common/page_alloc.c                 |  4 ++--
 xen/include/xen/bitops.h                | 24 ++++++++++++++++++++++++
 8 files changed, 61 insertions(+), 21 deletions(-)

diff --git a/xen/arch/arm/include/asm/arm32/bitops.h b/xen/arch/arm/include/asm/arm32/bitops.h
index d0309d47c1..9ee96f568b 100644
--- a/xen/arch/arm/include/asm/arm32/bitops.h
+++ b/xen/arch/arm/include/asm/arm32/bitops.h
@@ -1,7 +1,7 @@
 #ifndef _ARM_ARM32_BITOPS_H
 #define _ARM_ARM32_BITOPS_H
 
-#define flsl fls
+#define arch_flsl arch_fls
 
 /*
  * Little endian assembly bitops.  nr = 0 -> byte 0 bit 0.
diff --git a/xen/arch/arm/include/asm/arm64/bitops.h b/xen/arch/arm/include/asm/arm64/bitops.h
index 906d84e5f2..d942077392 100644
--- a/xen/arch/arm/include/asm/arm64/bitops.h
+++ b/xen/arch/arm/include/asm/arm64/bitops.h
@@ -1,17 +1,15 @@
 #ifndef _ARM_ARM64_BITOPS_H
 #define _ARM_ARM64_BITOPS_H
 
-static inline int flsl(unsigned long x)
+static always_inline unsigned int arch_flsl(unsigned long x)
 {
         uint64_t ret;
 
-        if (__builtin_constant_p(x))
-               return generic_flsl(x);
-
         asm("clz\t%0, %1" : "=r" (ret) : "r" (x));
 
         return BITS_PER_LONG - ret;
 }
+#define arch_flsl arch_flsl
 
 /* Based on linux/include/asm-generic/bitops/find.h */
 
diff --git a/xen/arch/arm/include/asm/bitops.h b/xen/arch/arm/include/asm/bitops.h
index 8e16335e76..f428cf8338 100644
--- a/xen/arch/arm/include/asm/bitops.h
+++ b/xen/arch/arm/include/asm/bitops.h
@@ -78,17 +78,14 @@ bool clear_mask16_timeout(uint16_t mask, volatile void *p,
  * the clz instruction for much better code efficiency.
  */
 
-static inline int fls(unsigned int x)
+static always_inline unsigned int arch_fls(unsigned int x)
 {
-        int ret;
-
-        if (__builtin_constant_p(x))
-               return generic_fls(x);
+        unsigned int ret;
 
         asm("clz\t%"__OP32"0, %"__OP32"1" : "=r" (ret) : "r" (x));
         return 32 - ret;
 }
-
+#define arch_fls arch_fls
 
 #define arch_ffs(x) ({ unsigned int __t = (x); fls(ISOLATE_LSB(__t)); })
 #define arch_ffsl(x) ({ unsigned long __t = (x); flsl(ISOLATE_LSB(__t)); })
diff --git a/xen/arch/ppc/include/asm/bitops.h b/xen/arch/ppc/include/asm/bitops.h
index 049aa62b89..46154fc957 100644
--- a/xen/arch/ppc/include/asm/bitops.h
+++ b/xen/arch/ppc/include/asm/bitops.h
@@ -119,9 +119,6 @@ static inline int test_and_set_bit(unsigned int nr, volatile void *addr)
         (volatile unsigned int *)addr + BITOP_WORD(nr)) != 0;
 }
 
-#define flsl(x) generic_flsl(x)
-#define fls(x) generic_fls(x)
-
 /**
  * hweightN - returns the hamming weight of a N-bit word
  * @x: the word to weigh
diff --git a/xen/arch/x86/include/asm/bitops.h b/xen/arch/x86/include/asm/bitops.h
index 23f09fdb7a..17849fae97 100644
--- a/xen/arch/x86/include/asm/bitops.h
+++ b/xen/arch/x86/include/asm/bitops.h
@@ -425,20 +425,21 @@ static always_inline unsigned int arch_ffsl(unsigned long x)
  *
  * This is defined the same way as ffs.
  */
-static inline int flsl(unsigned long x)
+static always_inline unsigned int arch_flsl(unsigned long x)
 {
-    long r;
+    unsigned long r;
 
     asm ( "bsr %1,%0\n\t"
           "jnz 1f\n\t"
           "mov $-1,%0\n"
           "1:" : "=r" (r) : "rm" (x));
-    return (int)r+1;
+    return (unsigned int)r+1;
 }
+#define arch_flsl arch_flsl
 
-static inline int fls(unsigned int x)
+static always_inline unsigned int arch_fls(unsigned int x)
 {
-    int r;
+    unsigned int r;
 
     asm ( "bsr %1,%0\n\t"
           "jnz 1f\n\t"
@@ -446,6 +447,7 @@ static inline int fls(unsigned int x)
           "1:" : "=r" (r) : "rm" (x));
     return r + 1;
 }
+#define arch_fls arch_fls
 
 /**
  * hweightN - returns the hamming weight of a N-bit word
diff --git a/xen/common/bitops.c b/xen/common/bitops.c
index a8c32f6767..95bc47176b 100644
--- a/xen/common/bitops.c
+++ b/xen/common/bitops.c
@@ -62,9 +62,31 @@ static void test_ffs(void)
     CHECK(ffs64, (uint64_t)0x8000000000000000, 64);
 }
 
+static void test_fls(void)
+{
+    /* unsigned int ffs(unsigned int) */
+    CHECK(fls, 1, 1);
+    CHECK(fls, 3, 2);
+    CHECK(fls, 3U << 30, 32);
+
+    /* unsigned int flsl(unsigned long) */
+    CHECK(flsl, 1, 1);
+    CHECK(flsl, 1UL << (BITS_PER_LONG - 1), BITS_PER_LONG);
+#if BITS_PER_LONG > 32
+    CHECK(flsl, 3UL << 32, 34);
+#endif
+
+    /* unsigned int fls64(uint64_t) */
+    CHECK(fls64, 1, 1);
+    CHECK(fls64, 0x00000000C0000000ULL, 32);
+    CHECK(fls64, 0x0000000180000000ULL, 33);
+    CHECK(fls64, 0xC000000000000000ULL, 64);
+}
+
 static int __init cf_check test_bitops(void)
 {
     test_ffs();
+    test_fls();
 
     return 0;
 }
diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index be4ba3962a..eed6b2a901 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -1842,7 +1842,7 @@ static void _init_heap_pages(const struct page_info *pg,
          * Note that the value of ffsl() and flsl() starts from 1 so we need
          * to decrement it by 1.
          */
-        unsigned int inc_order = min(MAX_ORDER, flsl(e - s) - 1);
+        unsigned int inc_order = min(MAX_ORDER + 0U, flsl(e - s) - 1);
 
         if ( s )
             inc_order = min(inc_order, ffsl(s) - 1U);
@@ -2266,7 +2266,7 @@ void __init xenheap_max_mfn(unsigned long mfn)
     ASSERT(!first_node_initialised);
     ASSERT(!xenheap_bits);
     BUILD_BUG_ON((PADDR_BITS - PAGE_SHIFT) >= BITS_PER_LONG);
-    xenheap_bits = min(flsl(mfn + 1) - 1 + PAGE_SHIFT, PADDR_BITS);
+    xenheap_bits = min(flsl(mfn + 1) - 1 + PAGE_SHIFT, PADDR_BITS + 0U);
     printk(XENLOG_INFO "Xen heap: %u bits\n", xenheap_bits);
 }
 
diff --git a/xen/include/xen/bitops.h b/xen/include/xen/bitops.h
index 6eeeff0117..59b8028894 100644
--- a/xen/include/xen/bitops.h
+++ b/xen/include/xen/bitops.h
@@ -200,6 +200,30 @@ static always_inline bool test_bit(int nr, const volatile void *addr)
     test_bit(nr, addr);                                 \
 })
 
+static always_inline __pure unsigned int fls(unsigned int x)
+{
+    if ( __builtin_constant_p(x) )
+        return generic_fls(x);
+
+#ifndef arch_fls
+#define arch_fls generic_fls
+#endif
+
+    return arch_fls(x);
+}
+
+static always_inline __pure unsigned int flsl(unsigned long x)
+{
+    if ( __builtin_constant_p(x) )
+        return generic_flsl(x);
+
+#ifndef arch_flsl
+#define arch_flsl generic_flsl
+#endif
+
+    return arch_flsl(x);
+}
+
 /*
  * Find First Set bit.  Bits are labelled from 1.
  */
-- 
2.45.0

On 17.05.2024 15:54, Oleksii Kurochko wrote:
> To avoid the compilation error below, it is needed to update to places
> in common/page_alloc.c where flsl() is used as now flsl() returns unsigned int:
> 
> ./include/xen/kernel.h:18:21: error: comparison of distinct pointer types lacks a cast [-Werror]
>        18 |         (void) (&_x == &_y);            \
>           |                     ^~
>     common/page_alloc.c:1843:34: note: in expansion of macro 'min'
>      1843 |         unsigned int inc_order = min(MAX_ORDER, flsl(e - s) - 1);
> 
> generic_fls{l} was used instead of __builtin_clz{l}(x) as if x is 0,
> the result in undefined.
> 
> The prototype of the per-architecture fls{l}() functions was changed to
> return 'unsigned int' to align with the generic implementation of these
> functions and avoid introducing signed/unsigned mismatches.
> 
> Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
> ---
>  The patch is almost independent from Andrew's patch series
>  ( https://lore.kernel.org/xen-devel/20240313172716.2325427-1-andrew.cooper3@citrix.com/T/#t)
>  except test_fls() function which IMO can be merged as a separate patch after Andrew's patch
>  will be fully ready.

If there wasn't this dependency (I don't think it's "almost independent"),
I'd be offering R-b with again one nit below.

> --- a/xen/arch/x86/include/asm/bitops.h
> +++ b/xen/arch/x86/include/asm/bitops.h
> @@ -425,20 +425,21 @@ static always_inline unsigned int arch_ffsl(unsigned long x)
>   *
>   * This is defined the same way as ffs.
>   */
> -static inline int flsl(unsigned long x)
> +static always_inline unsigned int arch_flsl(unsigned long x)
>  {
> -    long r;
> +    unsigned long r;
>  
>      asm ( "bsr %1,%0\n\t"
>            "jnz 1f\n\t"
>            "mov $-1,%0\n"
>            "1:" : "=r" (r) : "rm" (x));
> -    return (int)r+1;
> +    return (unsigned int)r+1;

Since you now touch this, you'd better tidy it at the same time:

    return r + 1;

(i.e. style and no need for a cast).

Jan

On Tue, 2024-05-21 at 13:18 +0200, Jan Beulich wrote:
> On 17.05.2024 15:54, Oleksii Kurochko wrote:
> > To avoid the compilation error below, it is needed to update to
> > places
> > in common/page_alloc.c where flsl() is used as now flsl() returns
> > unsigned int:
> > 
> > ./include/xen/kernel.h:18:21: error: comparison of distinct pointer
> > types lacks a cast [-Werror]
> >        18 |         (void) (&_x == &_y);            \
> >           |                     ^~
> >     common/page_alloc.c:1843:34: note: in expansion of macro 'min'
> >      1843 |         unsigned int inc_order = min(MAX_ORDER, flsl(e
> > - s) - 1);
> > 
> > generic_fls{l} was used instead of __builtin_clz{l}(x) as if x is
> > 0,
> > the result in undefined.
> > 
> > The prototype of the per-architecture fls{l}() functions was
> > changed to
> > return 'unsigned int' to align with the generic implementation of
> > these
> > functions and avoid introducing signed/unsigned mismatches.
> > 
> > Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
> > ---
> >  The patch is almost independent from Andrew's patch series
> >  (
> > https://lore.kernel.org/xen-devel/20240313172716.2325427-1-andrew.cooper3@citrix.com/T/#t
> > )
> >  except test_fls() function which IMO can be merged as a separate
> > patch after Andrew's patch
> >  will be fully ready.
> 
> If there wasn't this dependency (I don't think it's "almost
> independent"),
> I'd be offering R-b with again one nit below.

Aren't all changes, except those in xen/common/bitops.c, independent? I
could move these changes in xen/common/bitops.c to a separate commit. I
think it is safe to commit them ( an introduction of common logic for
fls{l}() and tests ) separately since the CI tests have passed.

~ Oleksii

> 
> > --- a/xen/arch/x86/include/asm/bitops.h
> > +++ b/xen/arch/x86/include/asm/bitops.h
> > @@ -425,20 +425,21 @@ static always_inline unsigned int
> > arch_ffsl(unsigned long x)
> >   *
> >   * This is defined the same way as ffs.
> >   */
> > -static inline int flsl(unsigned long x)
> > +static always_inline unsigned int arch_flsl(unsigned long x)
> >  {
> > -    long r;
> > +    unsigned long r;
> >  
> >      asm ( "bsr %1,%0\n\t"
> >            "jnz 1f\n\t"
> >            "mov $-1,%0\n"
> >            "1:" : "=r" (r) : "rm" (x));
> > -    return (int)r+1;
> > +    return (unsigned int)r+1;
> 
> Since you now touch this, you'd better tidy it at the same time:
> 
>     return r + 1;
> 
> (i.e. style and no need for a cast).
> 
> Jan

On 22.05.2024 09:37, Oleksii K. wrote:
> On Tue, 2024-05-21 at 13:18 +0200, Jan Beulich wrote:
>> On 17.05.2024 15:54, Oleksii Kurochko wrote:
>>> To avoid the compilation error below, it is needed to update to
>>> places
>>> in common/page_alloc.c where flsl() is used as now flsl() returns
>>> unsigned int:
>>>
>>> ./include/xen/kernel.h:18:21: error: comparison of distinct pointer
>>> types lacks a cast [-Werror]
>>>        18 |         (void) (&_x == &_y);            \
>>>           |                     ^~
>>>     common/page_alloc.c:1843:34: note: in expansion of macro 'min'
>>>      1843 |         unsigned int inc_order = min(MAX_ORDER, flsl(e
>>> - s) - 1);
>>>
>>> generic_fls{l} was used instead of __builtin_clz{l}(x) as if x is
>>> 0,
>>> the result in undefined.
>>>
>>> The prototype of the per-architecture fls{l}() functions was
>>> changed to
>>> return 'unsigned int' to align with the generic implementation of
>>> these
>>> functions and avoid introducing signed/unsigned mismatches.
>>>
>>> Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
>>> ---
>>>  The patch is almost independent from Andrew's patch series
>>>  (
>>> https://lore.kernel.org/xen-devel/20240313172716.2325427-1-andrew.cooper3@citrix.com/T/#t
>>> )
>>>  except test_fls() function which IMO can be merged as a separate
>>> patch after Andrew's patch
>>>  will be fully ready.
>>
>> If there wasn't this dependency (I don't think it's "almost
>> independent"),
>> I'd be offering R-b with again one nit below.
> 
> Aren't all changes, except those in xen/common/bitops.c, independent? I
> could move these changes in xen/common/bitops.c to a separate commit. I
> think it is safe to commit them ( an introduction of common logic for
> fls{l}() and tests ) separately since the CI tests have passed.

Technically they might be, but contextually there are further conflicts.
Just try "patch --dry-run" on top of a plain staging tree. You really
need to settle, perhaps consulting Andrew, whether you want to go on top
of his change, or ahead of it. I'm not willing to approve a patch that's
presented one way but then is (kind of) expected to go in the other way.

Jan

Hi,

On 22/05/2024 09:15, Jan Beulich wrote:
> On 22.05.2024 09:37, Oleksii K. wrote:
>> On Tue, 2024-05-21 at 13:18 +0200, Jan Beulich wrote:
>>> On 17.05.2024 15:54, Oleksii Kurochko wrote:
>>>> To avoid the compilation error below, it is needed to update to
>>>> places
>>>> in common/page_alloc.c where flsl() is used as now flsl() returns
>>>> unsigned int:
>>>>
>>>> ./include/xen/kernel.h:18:21: error: comparison of distinct pointer
>>>> types lacks a cast [-Werror]
>>>>         18 |         (void) (&_x == &_y);            \
>>>>            |                     ^~
>>>>      common/page_alloc.c:1843:34: note: in expansion of macro 'min'
>>>>       1843 |         unsigned int inc_order = min(MAX_ORDER, flsl(e
>>>> - s) - 1);
>>>>
>>>> generic_fls{l} was used instead of __builtin_clz{l}(x) as if x is
>>>> 0,
>>>> the result in undefined.
>>>>
>>>> The prototype of the per-architecture fls{l}() functions was
>>>> changed to
>>>> return 'unsigned int' to align with the generic implementation of
>>>> these
>>>> functions and avoid introducing signed/unsigned mismatches.
>>>>
>>>> Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
>>>> ---
>>>>   The patch is almost independent from Andrew's patch series
>>>>   (
>>>> https://lore.kernel.org/xen-devel/20240313172716.2325427-1-andrew.cooper3@citrix.com/T/#t
>>>> )
>>>>   except test_fls() function which IMO can be merged as a separate
>>>> patch after Andrew's patch
>>>>   will be fully ready.
>>>
>>> If there wasn't this dependency (I don't think it's "almost
>>> independent"),
>>> I'd be offering R-b with again one nit below.
>>
>> Aren't all changes, except those in xen/common/bitops.c, independent? I
>> could move these changes in xen/common/bitops.c to a separate commit. I
>> think it is safe to commit them ( an introduction of common logic for
>> fls{l}() and tests ) separately since the CI tests have passed.
> 
> Technically they might be, but contextually there are further conflicts.
> Just try "patch --dry-run" on top of a plain staging tree. You really
> need to settle, perhaps consulting Andrew, whether you want to go on top
> of his change, or ahead of it. I'm not willing to approve a patch that's
> presented one way but then is (kind of) expected to go in the other way.

I agree with what Jan wrote. I don't have any strong opinion on which 
order they should be merged. But, if your series is intended to be 
merged before Andrew's one then please rebase to vanilla staging.

I looked at the rest of the patch and it LGTM.

Cheers,

-- 
Julien Grall