linux-kernel - Re: [PATCH v3 1/2] asm-generic: Unify uapi bitsperlong.h for arm64, riscv and loongarch

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Message-ID: <20230729174617.GA1229655@dev-arch.thelio-3990X>
Date:   Sat, 29 Jul 2023 10:46:17 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Tiezhu Yang <yangtiezhu@...ngson.cn>,
        linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, loongarch@...ts.linux.dev,
        Linux-Arch <linux-arch@...r.kernel.org>, bpf@...r.kernel.org,
        linux-perf-users@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org, loongson-kernel@...ts.loongnix.cn
Subject: Re: [PATCH v3 1/2] asm-generic: Unify uapi bitsperlong.h for arm64,
 riscv and loongarch

On Sat, Jul 29, 2023 at 09:59:23AM +0200, Arnd Bergmann wrote:
> On Sat, Jul 29, 2023, at 01:44, Nathan Chancellor wrote:
> > On Fri, Jul 28, 2023 at 10:56:38PM +0200, Arnd Bergmann wrote:
> 
> >     DESCEND objtool
> >   In file included from 
> > /usr/include/aarch64-linux-gnu/asm/bitsperlong.h:1,
> >                    from /usr/include/asm-generic/int-ll64.h:12,
> >                    from /usr/include/asm-generic/types.h:7,
> >                    from /usr/include/aarch64-linux-gnu/asm/types.h:1,
> >                    from /linux-stable/tools/include/linux/types.h:13,
> >                    from 
> > /linux-stable/tools/arch/x86/include/asm/orc_types.h:9,
> >                    from /linux-stable/scripts/sorttable.h:96,
> >                    from /linux-stable/scripts/sorttable.c:201:
> >   /linux-stable/tools/include/asm-generic/bitsperlong.h:14:2: error: 
> > #error Inconsistent word size. Check asm/bitsperlong.h
> >      14 | #error Inconsistent word size. Check asm/bitsperlong.h
> >         |  ^~~~~
> >   make[3]: *** [/linux-stable/scripts/Makefile.host:114: 
> > scripts/sorttable] Error 1
> >   ...
> >
> >> I also noticed that your command line includes CROSS_COMPILE=x86_64-linux-
> >> rather than CROSS_COMPILE=x86_64-linux-gnu-
> >
> > Right, as I was reproducing this with your kernel.org GCC for
> > CROSS_COMPILE and Fedora's GCC for HOSTCC, since I wanted to make sure
> > this was not some issue with clang (which it does not appear to be).
> 
> Ok, it's beginning to make more sense to me now. I see
> that the tools/arch/x86/include/asm/orc_types.h comes from
> the x86_64 target build and is intentional, as sorttable.c
> needs to access the ORC information. Here the Makefile does
> 
> ifdef CONFIG_UNWINDER_ORC
> ifeq ($(ARCH),x86_64)
> ARCH := x86
> endif
> HOSTCFLAGS_sorttable.o += -I$(srctree)/tools/arch/x86/include
> HOSTCFLAGS_sorttable.o += -DUNWINDER_ORC_ENABLED
> endif
> 
> in order to get the ORC definitions from asm/orc_types.h, but
> then it looks like it also gets the uapi/asm/bitsperlong.h
> header from there which contains
> 
> #if defined(__x86_64__) && !defined(__ILP32__)
> # define __BITS_PER_LONG 64
> #else
> # define __BITS_PER_LONG 32
> #endif
> 
> and this would set __BITS_PER_LONG to 32 on arm64.
> 
> However, I don't see this actually being included on my
> machine. Can you dump the sorttable.c preprocessor output
> with your setup, using -fdirectives-only, so we can see
> which of the two (__BITS_PER_LONG or BITS_PER_LONG) is
> actually wrong and triggers the sanity check?

Sure thing, this is the output of:

  $ gcc -I/linux-stable/tools/include -I/linux-stable/tools/arch/x86/include -DUNWINDER_ORC_ENABLED -I ./scripts -E -fdirectives-only /linux-stable/scripts/sorttable.c

https://gist.github.com/nathanchance/d2c3e58230930317dc84aff80fef38bf

> What I see on my machine is that both definitions come
> from the local tools/include/ headers, not from the
> installed system headers, so I'm still doing something
> wrong in my installation:

Just to make sure, you have the 6.5-rc1+ headers installed and you are
attempting to build the host tools from an earlier Linux release than
6.5-rc1? I don't see a problem with building these host programs on
mainline/6.5, I see this issue when building them in older stable
releases (my reproduction so far has been on 6.4 but I see it when
building all currently supported long term stable releases) when I have
the 6.5-rc1+ headers installed.

> ./tools/include/uapi/asm-generic/bitsperlong.h
> #define __BITS_PER_LONG (__CHAR_BIT__ * __SIZEOF_LONG__)

Because this is the mainline version, whereas the stable version is:

#ifndef _UAPI__ASM_GENERIC_BITS_PER_LONG
#define _UAPI__ASM_GENERIC_BITS_PER_LONG

/*
 * There seems to be no way of detecting this automatically from user
 * space, so 64 bit architectures should override this in their
 * bitsperlong.h. In particular, an architecture that supports
 * both 32 and 64 bit user space must not rely on CONFIG_64BIT
 * to decide it, but rather check a compiler provided macro.
 */
#ifndef __BITS_PER_LONG
#define __BITS_PER_LONG 32
#endif

#endif /* _UAPI__ASM_GENERIC_BITS_PER_LONG */

which seems to be where the mismatch is coming from?

> ./tools/include/asm-generic/bitsperlong.h
> #define BITS_PER_LONG (__CHAR_BIT__ * __SIZEOF_LONG__)
> 
> Neither of these files actually contains the sanity
> check in linux-6.5-rc3, and comparing these is clearly
> nonsensical, as they are defined the same way (rather
> than checking CONFIG_64BIT), but also I don't see why
> there is both a uapi/ version and a non-uapi version
> in what is meant to be a userspace header.

May be worth looping in the tools/ folks, since that whole directory is
rather special IMO...

Cheers,
Nathan