Re: [PATCH] alpha/elf: Fix misc/setarch test of util-linux by removing 32bit support

[Richard Henderson <richard.henderson@xxxxxxxxxx>]

On 1/10/25 16:16, Eric W. Biederman wrote:
> Richard Henderson <richard.henderson@xxxxxxxxxx> writes[1]:
>
> > There was a Spec benchmark (I forget which) which was memory bound and ran
> > twice as fast with 32-bit pointers.
> >
> > I copied the idea from DEC to the ELF abi, but never did all the other work
> > to allow the toolchain to take advantage.
> >
> > Amusingly, a later Spec changed the benchmark data sets to not fit into a
> > 32-bit address space, specifically because of this.
> >
> > I expect one could delete the ELF bit and personality and no one would
> > notice. Not even the 10 remaining Alpha users.
>
> In [2] it was pointed out that parts of setarch weren't working
> properly on alpha because it has it's own SET_PERSONALITY
> implementation.  In the discussion that followed Richard Henderson
> pointed out that the 32bit pointer support for alpha was never
> completed.
>
> Fix this by removing alpha's 32bit pointer support.
>
> As a bit of paranoia refuse to execute any alpha binaries that hafe
> the EF_ALPHA_32BIT flag set.  Just to fail explicitly in case someone
> somewhere has binaries that trying to use alpha's 32bit pointer
> support.
>
> [1] https://lkml.kernel.org/r/CAFXwXrkgu=4Qn-v1PjnOR4SG0oUb9LSa0g6QXpBq4ttm52pJOQ@xxxxxxxxxxxxxx
> [2] https://lkml.kernel.org/r/20250103140148.370368-1-glaubitz@xxxxxxxxxxxxxxxxxxx
> Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>

Thanks for cleaning this up.
Reviewed-by: Richard Henderson <richard.henderson@xxxxxxxxxx>


r~


> ---
>   arch/alpha/include/asm/elf.h       |  6 +-----
>   arch/alpha/include/asm/pgtable.h   |  2 +-
>   arch/alpha/include/asm/processor.h |  8 ++------
>   arch/alpha/kernel/osf_sys.c        | 11 ++---------
>   4 files changed, 6 insertions(+), 21 deletions(-)
>
> diff --git a/arch/alpha/include/asm/elf.h b/arch/alpha/include/asm/elf.h
> index 4d7c46f50382..50c82187e60e 100644
> --- a/arch/alpha/include/asm/elf.h
> +++ b/arch/alpha/include/asm/elf.h
> @@ -74,7 +74,7 @@ typedef elf_fpreg_t elf_fpregset_t[ELF_NFPREG];
>   /*
>    * This is used to ensure we don't load something for the wrong architecture.
>    */
> -#define elf_check_arch(x) ((x)->e_machine == EM_ALPHA)
> +#define elf_check_arch(x) (((x)->e_machine == EM_ALPHA) && !((x)->e_flags & EF_ALPHA_32BIT))
>   
>   /*
>    * These are used to set parameters in the core dumps.
> @@ -137,10 +137,6 @@ extern int dump_elf_task(elf_greg_t *dest, struct task_struct *task);
>   	: amask (AMASK_CIX) ? "ev6" : "ev67");	\
>   })
>   
> -#define SET_PERSONALITY(EX)					\
> -	set_personality(((EX).e_flags & EF_ALPHA_32BIT)		\
> -	   ? PER_LINUX_32BIT : PER_LINUX)
> -
>   extern int alpha_l1i_cacheshape;
>   extern int alpha_l1d_cacheshape;
>   extern int alpha_l2_cacheshape;
> diff --git a/arch/alpha/include/asm/pgtable.h b/arch/alpha/include/asm/pgtable.h
> index 635f0a5f5bbd..02e8817a8921 100644
> --- a/arch/alpha/include/asm/pgtable.h
> +++ b/arch/alpha/include/asm/pgtable.h
> @@ -360,7 +360,7 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
>   
>   extern void paging_init(void);
>   
> -/* We have our own get_unmapped_area to cope with ADDR_LIMIT_32BIT.  */
> +/* We have our own get_unmapped_area */
>   #define HAVE_ARCH_UNMAPPED_AREA
>   
>   #endif /* _ALPHA_PGTABLE_H */
> diff --git a/arch/alpha/include/asm/processor.h b/arch/alpha/include/asm/processor.h
> index 55bb1c09fd39..5dce5518a211 100644
> --- a/arch/alpha/include/asm/processor.h
> +++ b/arch/alpha/include/asm/processor.h
> @@ -8,23 +8,19 @@
>   #ifndef __ASM_ALPHA_PROCESSOR_H
>   #define __ASM_ALPHA_PROCESSOR_H
>   
> -#include <linux/personality.h>	/* for ADDR_LIMIT_32BIT */
> -
>   /*
>    * We have a 42-bit user address space: 4TB user VM...
>    */
>   #define TASK_SIZE (0x40000000000UL)
>   
> -#define STACK_TOP \
> -  (current->personality & ADDR_LIMIT_32BIT ? 0x80000000 : 0x00120000000UL)
> +#define STACK_TOP (0x00120000000UL)
>   
>   #define STACK_TOP_MAX	0x00120000000UL
>   
>   /* This decides where the kernel will search for a free chunk of vm
>    * space during mmap's.
>    */
> -#define TASK_UNMAPPED_BASE \
> -  ((current->personality & ADDR_LIMIT_32BIT) ? 0x40000000 : TASK_SIZE / 2)
> +#define TASK_UNMAPPED_BASE (TASK_SIZE / 2)
>   
>   /* This is dead.  Everything has been moved to thread_info.  */
>   struct thread_struct { };
> diff --git a/arch/alpha/kernel/osf_sys.c b/arch/alpha/kernel/osf_sys.c
> index 86185021f75a..a08e8edef1a4 100644
> --- a/arch/alpha/kernel/osf_sys.c
> +++ b/arch/alpha/kernel/osf_sys.c
> @@ -1210,8 +1210,7 @@ SYSCALL_DEFINE1(old_adjtimex, struct timex32 __user *, txc_p)
>   	return ret;
>   }
>   
> -/* Get an address range which is currently unmapped.  Similar to the
> -   generic version except that we know how to honor ADDR_LIMIT_32BIT.  */
> +/* Get an address range which is currently unmapped. */
>   
>   static unsigned long
>   arch_get_unmapped_area_1(unsigned long addr, unsigned long len,
> @@ -1230,13 +1229,7 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
>   		       unsigned long len, unsigned long pgoff,
>   		       unsigned long flags, vm_flags_t vm_flags)
>   {
> -	unsigned long limit;
> -
> -	/* "32 bit" actually means 31 bit, since pointers sign extend.  */
> -	if (current->personality & ADDR_LIMIT_32BIT)
> -		limit = 0x80000000;
> -	else
> -		limit = TASK_SIZE;
> +	unsigned long limit = TASK_SIZE;
>   
>   	if (len > limit)
>   		return -ENOMEM;