From: David Laight <David.Laight@ACULAB.COM>
To: 'Segher Boessenkool' <segher@kernel.crashing.org>,
Stafford Horne <shorne@gmail.com>
Cc: Rich Felker <dalias@libc.org>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
"x86@kernel.org" <x86@kernel.org>, Guo Ren <guoren@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
"linux-riscv@lists.infradead.org"
<linux-riscv@lists.infradead.org>,
"Will Deacon" <will@kernel.org>, Jonas Bonn <jonas@southpole.se>,
Rob Herring <robh@kernel.org>,
Florian Fainelli <f.fainelli@gmail.com>,
Frank Rowand <frowand.list@gmail.com>,
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Russell King <linux@armlinux.org.uk>,
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Subject: RE: [PATCH 06/12] openrisc: Use of_get_cpu_hwid()
Date: Thu, 7 Oct 2021 07:53:01 +0000 [thread overview]
Message-ID: <c81b9c01650e487785b02f6562791556@AcuMS.aculab.com> (raw)
In-Reply-To: <20211006212728.GM10333@gate.crashing.org>
From: Segher Boessenkool
> Sent: 06 October 2021 22:27
>
> On Thu, Oct 07, 2021 at 05:44:00AM +0900, Stafford Horne wrote:
> > You have defined of_get_cpu_hwid to return u64, will this create compiler
> > warnings when since we are storing a u64 into a u32?
> >
> > It seems only if we make with W=3.
>
> Yes. This is done by -Wconversion, "Warn for implicit conversions that
> may alter a value."
>
> > I thought we usually warned on this.
The microsoft compiler does - best to turn all those warnings off.
> This warning is not in -Wall or -Wextra either, it suffers too much from
> false positives. It is very natural to just ignore the high bits of
> modulo types (which is what "unsigned" types *are*). Or the bits that
> "fall off" on a conversion. The C standard makes this required
> behaviour, it is useful, and it is the only convenient way of getting
> this!
I've also seen a compiler convert:
struct->char_member = (char)(int_val & 0xff);
into:
reg = int_val;
reg &= 0xff; // for the & 0xff
reg &= 0xff; // for the cast
struct->char_member = low_8bits(reg);
You really don't want the extra noise.
I'll bet that (char)int_val is actually an arithmetic expression.
So its type will be 'int'.
David
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Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2021-10-07 7:53 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-06 16:43 [PATCH 00/12] DT: CPU h/w id parsing clean-ups and cacheinfo id support Rob Herring
2021-10-06 16:43 ` [PATCH 01/12] of: Add of_get_cpu_hwid() to read hardware ID from CPU nodes Rob Herring
2021-10-18 13:26 ` Sudeep Holla
2021-10-06 16:43 ` [PATCH 02/12] ARM: Use of_get_cpu_hwid() Rob Herring
2021-10-06 16:43 ` [PATCH 03/12] ARM: broadcom: " Rob Herring
2021-10-07 2:24 ` Florian Fainelli
2021-10-06 16:43 ` [PATCH 04/12] arm64: " Rob Herring
2021-10-07 8:07 ` Will Deacon
2021-10-18 13:27 ` Sudeep Holla
2021-10-06 16:43 ` [PATCH 05/12] csky: " Rob Herring
2021-10-06 16:43 ` [PATCH 06/12] openrisc: " Rob Herring
2021-10-06 20:44 ` Stafford Horne
2021-10-06 21:08 ` Rob Herring
2021-10-06 21:25 ` Stafford Horne
2021-10-06 21:27 ` Segher Boessenkool
2021-10-06 22:37 ` Stafford Horne
2021-10-07 7:53 ` David Laight [this message]
2021-10-06 16:43 ` [PATCH 07/12] powerpc: " Rob Herring
2021-10-08 11:01 ` Michael Ellerman
2021-10-06 16:43 ` [PATCH 08/12] riscv: " Rob Herring
2021-10-06 16:43 ` [PATCH 09/12] sh: " Rob Herring
2021-10-27 14:26 ` Rich Felker
2021-10-06 16:43 ` [PATCH 10/12] x86: dt: " Rob Herring
2021-10-06 16:43 ` [PATCH 11/12] cacheinfo: Allow for >32-bit cache 'id' Rob Herring
2021-10-18 13:30 ` Sudeep Holla
2021-10-06 16:43 ` [PATCH 12/12] cacheinfo: Set cache 'id' based on DT data Rob Herring
2021-10-18 13:31 ` Sudeep Holla
2021-10-07 2:24 ` [PATCH 00/12] DT: CPU h/w id parsing clean-ups and cacheinfo id support Florian Fainelli
2021-10-20 18:47 ` Rob Herring
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