Re: [PATCH 07/15] binfmt_flat: use __be32 for the on-disk format

From: Vladimir Murzin <vladimir.murzin@arm.com>
To: Christoph Hellwig <hch@lst.de>, Greg Ungerer <gerg@linux-m68k.org>
Cc: uclinux-h8-devel@lists.sourceforge.jp,
	linux-xtensa@linux-xtensa.org, Michal Simek <monstr@monstr.eu>,
	linux-c6x-dev@linux-c6x.org, linux-sh@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-m68k@lists.linux-m68k.org,
	linux-riscv@lists.infradead.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 07/15] binfmt_flat: use __be32 for the on-disk format
Date: Tue, 11 Jun 2019 09:57:00 +0000	[thread overview]
Message-ID: <462a7406-19df-7910-4499-8f0acd52bc82@arm.com> (raw)
In-Reply-To: <20190610212015.9157-8-hch@lst.de>

On 6/10/19 10:20 PM, Christoph Hellwig wrote:
> So far binfmt_flat has onl been supported on 32-bit platforms, so the
			^^^^
			only
> variable size of the fields didn't matter.  But the upcoming RISC-V
> nommu port supports 64-bit CPUs, and we now have a conflict between
> the elf2flt creation tool that always uses 32-bit fields and the kernel
> that uses (unsigned) long field.  Switch to the userspace view as the
> rest of the binfmt_flat format is completely architecture neutral,
> and binfmt_flat isn't the right binary format for huge executables to
> start with.
> 
> While we're at it also ensure these fields are using __be types as
> they big endian and are byteswapped when loaded.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> wip
  ^^^
Unintended?

> ---
>  include/linux/flat.h | 48 ++++++++++++++++++++++----------------------
>  1 file changed, 24 insertions(+), 24 deletions(-)

With comment message fixed:

Reviewed-by: Vladimir Murzin <vladimir.murzin@arm.com>

> 
> diff --git a/include/linux/flat.h b/include/linux/flat.h
> index 21d901ba191b..59e892d5fadb 100644
> --- a/include/linux/flat.h
> +++ b/include/linux/flat.h
> @@ -24,26 +24,26 @@
>   */
>  
>  struct flat_hdr {
> -	char magic[4];
> -	unsigned long rev;          /* version (as above) */
> -	unsigned long entry;        /* Offset of first executable instruction
> -	                               with text segment from beginning of file */
> -	unsigned long data_start;   /* Offset of data segment from beginning of
> -	                               file */
> -	unsigned long data_end;     /* Offset of end of data segment
> -	                               from beginning of file */
> -	unsigned long bss_end;      /* Offset of end of bss segment from beginning
> -	                               of file */
> +	char	magic[4];
> +	__be32	rev;          /* version (as above) */
> +	__be32	entry;        /* Offset of first executable instruction
> +				 with text segment from beginning of file */
> +	__be32	data_start;   /* Offset of data segment from beginning of
> +				 file */
> +	__be32	data_end;     /* Offset of end of data segment from beginning
> +				 of file */
> +	__be32	bss_end;      /* Offset of end of bss segment from beginning
> +				 of file */
>  
>  	/* (It is assumed that data_end through bss_end forms the bss segment.) */
>  
> -	unsigned long stack_size;   /* Size of stack, in bytes */
> -	unsigned long reloc_start;  /* Offset of relocation records from
> -	                               beginning of file */
> -	unsigned long reloc_count;  /* Number of relocation records */
> -	unsigned long flags;
> -	unsigned long build_date;   /* When the program/library was built */
> -	unsigned long filler[5];    /* Reservered, set to zero */
> +	__be32	stack_size;   /* Size of stack, in bytes */
> +	__be32	reloc_start;  /* Offset of relocation records from beginning of
> +				 file */
> +	__be32	reloc_count;  /* Number of relocation records */
> +	__be32	flags;
> +	__be32	build_date;   /* When the program/library was built */
> +	__u32	filler[5];    /* Reservered, set to zero */
>  };
>  
>  #define FLAT_FLAG_RAM    0x0001 /* load program entirely into RAM */
> @@ -67,19 +67,19 @@ struct flat_hdr {
>  #define OLD_FLAT_RELOC_TYPE_BSS		2
>  
>  typedef union {
> -	unsigned long	value;
> +	u32		value;
>  	struct {
>  # if defined(mc68000) && !defined(CONFIG_COLDFIRE)
> -		signed long offset : 30;
> -		unsigned long type : 2;
> +		s32	offset : 30;
> +		u32	type : 2;
>  #   	define OLD_FLAT_FLAG_RAM    0x1 /* load program entirely into RAM */
>  # elif defined(__BIG_ENDIAN_BITFIELD)
> -		unsigned long type : 2;
> -		signed long offset : 30;
> +		u32	type : 2;
> +		s32	offset : 30;
>  #   	define OLD_FLAT_FLAG_RAM    0x1 /* load program entirely into RAM */
>  # elif defined(__LITTLE_ENDIAN_BITFIELD)
> -		signed long offset : 30;
> -		unsigned long type : 2;
> +		s32	offset : 30;
> +		u32	type : 2;
>  #   	define OLD_FLAT_FLAG_RAM    0x1 /* load program entirely into RAM */
>  # else
>  #   	error "Unknown bitfield order for flat files."
> 