Return type was left 'int' because of the following compilation error:
./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.
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 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 | 7 ++-----
xen/arch/ppc/include/asm/bitops.h | 3 ---
xen/arch/x86/include/asm/bitops.h | 6 ++++--
xen/common/bitops.c | 22 ++++++++++++++++++++++
xen/include/xen/bitops.h | 24 ++++++++++++++++++++++++
7 files changed, 55 insertions(+), 15 deletions(-)
diff --git a/xen/arch/arm/include/asm/arm32/bitops.h b/xen/arch/arm/include/asm/arm32/bitops.h
index d0309d47c1..5552d4e945 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 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 0efde29068..5f5d97faa0 100644
--- a/xen/arch/arm/include/asm/arm64/bitops.h
+++ b/xen/arch/arm/include/asm/arm64/bitops.h
@@ -22,17 +22,15 @@ static /*__*/always_inline unsigned long __ffs(unsigned long word)
*/
#define ffz(x) __ffs(~(x))
-static inline int flsl(unsigned long x)
+static inline 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..860d6d4689 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 inline int arch_fls(unsigned int x)
{
int ret;
- if (__builtin_constant_p(x))
- return generic_fls(x);
-
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 e2b6473c8c..ca308fd62b 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)
-
/* Based on linux/include/asm-generic/bitops/ffz.h */
/*
* ffz - find first zero in word.
diff --git a/xen/arch/x86/include/asm/bitops.h b/xen/arch/x86/include/asm/bitops.h
index 2b2d9219ef..5d5b9445c5 100644
--- a/xen/arch/x86/include/asm/bitops.h
+++ b/xen/arch/x86/include/asm/bitops.h
@@ -430,7 +430,7 @@ 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 int arch_flsl(unsigned long x)
{
long r;
@@ -440,8 +440,9 @@ static inline int flsl(unsigned long x)
"1:" : "=r" (r) : "rm" (x));
return (int)r+1;
}
+#define arch_flsl arch_flsl
-static inline int fls(unsigned int x)
+static always_inline int arch_fls(unsigned int x)
{
int r;
@@ -451,6 +452,7 @@ 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/include/xen/bitops.h b/xen/include/xen/bitops.h
index a41ec44064..a7edee4a95 100644
--- a/xen/include/xen/bitops.h
+++ b/xen/include/xen/bitops.h
@@ -196,6 +196,30 @@ static always_inline bool test_bit(int nr, const volatile void *addr)
test_bit(nr, addr); \
})
+static always_inline __pure 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 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.
*/
--
2.44.0On 17.04.2024 12:04, Oleksii Kurochko wrote: > Return type was left 'int' because of the following compilation error: > > ./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); Apart from this I'm okay with this patch, assuming Andrew's won't change in any conflicting way. As to the above - no, I don't see us having ffs() / ffsl() returning unsigned int, fls() / flsl() returning plain int. Even more so that, given the LHS variable's type, an unsigned quantity is really meant in the quoted code. Jan
On Thu, 2024-04-25 at 17:44 +0200, Jan Beulich wrote: > On 17.04.2024 12:04, Oleksii Kurochko wrote: > > Return type was left 'int' because of the following compilation > > error: > > > > ./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); > > Apart from this I'm okay with this patch, assuming Andrew's won't > change in > any conflicting way. As to the above - no, I don't see us having > ffs() / ffsl() > returning unsigned int, fls() / flsl() returning plain int. Even more > so that, > given the LHS variable's type, an unsigned quantity is really meant > in the > quoted code. If I understand you correctly, it's acceptable for fls() / flsl() to return 'int'. Therefore, I can update the commit message by removing the part mentioning the compilation error, as it's expected for fls() / flsl() to return 'int'. Is my understanding correct? ~ Oleksii
On 26.04.2024 10:21, Oleksii wrote: > On Thu, 2024-04-25 at 17:44 +0200, Jan Beulich wrote: >> On 17.04.2024 12:04, Oleksii Kurochko wrote: >>> Return type was left 'int' because of the following compilation >>> error: >>> >>> ./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); >> >> Apart from this I'm okay with this patch, assuming Andrew's won't >> change in >> any conflicting way. As to the above - no, I don't see us having >> ffs() / ffsl() >> returning unsigned int, fls() / flsl() returning plain int. Even more >> so that, >> given the LHS variable's type, an unsigned quantity is really meant >> in the >> quoted code. > If I understand you correctly, it's acceptable for fls() / flsl() to > return 'int'. Therefore, I can update the commit message by removing > the part mentioning the compilation error, as it's expected for fls() / > flsl() to return 'int'. Is my understanding correct? No. I firmly object to ffs() and fls() being different in their return types. I'm sorry, I realize now that my earlier wording was ambiguous (at least missing "but" after the comma). Jan
On Fri, 2024-04-26 at 12:51 +0200, Jan Beulich wrote:
> On 26.04.2024 10:21, Oleksii wrote:
> > On Thu, 2024-04-25 at 17:44 +0200, Jan Beulich wrote:
> > > On 17.04.2024 12:04, Oleksii Kurochko wrote:
> > > > Return type was left 'int' because of the following compilation
> > > > error:
> > > >
> > > > ./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);
> > >
> > > Apart from this I'm okay with this patch, assuming Andrew's won't
> > > change in
> > > any conflicting way. As to the above - no, I don't see us having
> > > ffs() / ffsl()
> > > returning unsigned int, fls() / flsl() returning plain int. Even
> > > more
> > > so that,
> > > given the LHS variable's type, an unsigned quantity is really
> > > meant
> > > in the
> > > quoted code.
> > If I understand you correctly, it's acceptable for fls() / flsl()
> > to
> > return 'int'. Therefore, I can update the commit message by
> > removing
> > the part mentioning the compilation error, as it's expected for
> > fls() /
> > flsl() to return 'int'. Is my understanding correct?
>
> No. I firmly object to ffs() and fls() being different in their
> return
> types. I'm sorry, I realize now that my earlier wording was ambiguous
> (at least missing "but" after the comma).
Thanks for clarifying.
I can change return type of fls() / flsl() to 'unsingned int' to be the
same as return type of ffs() / ffsl(), but then it will be needed to
add a cast in two places:
--- 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((unsigned int)MAX_ORDER,
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, (unsigned
int)PADDR_BITS);
printk(XENLOG_INFO "Xen heap: %u bits\n", xenheap_bits);
}
If it looks okay, then I'll do that in the next patch version.
~ Oleksii
On 26.04.2024 14:09, Oleksii wrote: > On Fri, 2024-04-26 at 12:51 +0200, Jan Beulich wrote: >> On 26.04.2024 10:21, Oleksii wrote: >>> On Thu, 2024-04-25 at 17:44 +0200, Jan Beulich wrote: >>>> On 17.04.2024 12:04, Oleksii Kurochko wrote: >>>>> Return type was left 'int' because of the following compilation >>>>> error: >>>>> >>>>> ./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); >>>> >>>> Apart from this I'm okay with this patch, assuming Andrew's won't >>>> change in >>>> any conflicting way. As to the above - no, I don't see us having >>>> ffs() / ffsl() >>>> returning unsigned int, fls() / flsl() returning plain int. Even >>>> more >>>> so that, >>>> given the LHS variable's type, an unsigned quantity is really >>>> meant >>>> in the >>>> quoted code. >>> If I understand you correctly, it's acceptable for fls() / flsl() >>> to >>> return 'int'. Therefore, I can update the commit message by >>> removing >>> the part mentioning the compilation error, as it's expected for >>> fls() / >>> flsl() to return 'int'. Is my understanding correct? >> >> No. I firmly object to ffs() and fls() being different in their >> return >> types. I'm sorry, I realize now that my earlier wording was ambiguous >> (at least missing "but" after the comma). > Thanks for clarifying. > > I can change return type of fls() / flsl() to 'unsingned int' to be the > same as return type of ffs() / ffsl(), but then it will be needed to > add a cast in two places: Except that no, it doesn't really need casts there. > --- 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((unsigned int)MAX_ORDER, > flsl(e - s) - 1); The preferred course of action would want to be to simply make MAX_ORDER expand to an unsigned constant. Depending on the amount of fallout, an alternative would be to use _AC(MAX_ORDER, U) here. Yet another alternative would be to use MAX_ORDER + 0U here, as iirc we do in a few other places, for similar purposes. Avoiding a cast here is not only shorter, but - see statements elsewhere - generally preferable. Jan
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