Re: [Xen-devel] [PATCH] xen/lockprof: Move .lockprofile.data into .rodata

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 24 Feb 2016, Andrew Cooper wrote:
> The entire contents of .lockprofile.data are unchanging pointers to
> lock_profile structure in .data.  Annotate the type as such, and link the
> section in .rodata.  As these are just pointers, 32byte alignment is
> unnecessary.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Ian Campbell <ian.campbell@xxxxxxxxxx>
> CC: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
> 
> v2:
>  * New
> v3:
>  * Explicitly introduce POINTER_ALIGN to avoid forcing 8 byte alignment on
>    arm32

Actually the way it is done in this patch, POINTER_ALIGN is 8 on arm64
and 4 on arm32 (see the definition of LONG_BYTEORDER in config.h). 

But I think it should still be OK.

Acked-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>


>  xen/arch/arm/xen.lds.S       | 15 ++++++++-------
>  xen/arch/x86/xen.lds.S       | 14 +++++++-------
>  xen/include/asm-arm/config.h |  1 +
>  xen/include/asm-x86/config.h |  1 +
>  xen/include/xen/spinlock.h   |  2 +-
>  5 files changed, 18 insertions(+), 15 deletions(-)
> 
> diff --git a/xen/arch/arm/xen.lds.S b/xen/arch/arm/xen.lds.S
> index f501a2f..1b5e516 100644
> --- a/xen/arch/arm/xen.lds.S
> +++ b/xen/arch/arm/xen.lds.S
> @@ -50,6 +50,14 @@ SECTIONS
>         __stop_bug_frames_2 = .;
>         *(.rodata)
>         *(.rodata.*)
> +
> +#ifdef LOCK_PROFILE
> +       . = ALIGN(POINTER_ALIGN);
> +       __lock_profile_start = .;
> +       *(.lockprofile.data)
> +       __lock_profile_end = .;
> +#endif
> +
>          _erodata = .;          /* End of read-only data */
>    } :text
>  
> @@ -83,13 +91,6 @@ SECTIONS
>         *(.data.rel.ro.*)
>    } :text
>  
> -#ifdef LOCK_PROFILE
> -  . = ALIGN(32);
> -  __lock_profile_start = .;
> -  .lockprofile.data : { *(.lockprofile.data) } :text
> -  __lock_profile_end = .;
> -#endif
> -
>    . = ALIGN(8);
>    .arch.info : {
>        _splatform = .;
> diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
> index 9fde1db..8390ec2 100644
> --- a/xen/arch/x86/xen.lds.S
> +++ b/xen/arch/x86/xen.lds.S
> @@ -65,6 +65,13 @@ SECTIONS
>  
>         *(.rodata)
>         *(.rodata.*)
> +
> +#ifdef LOCK_PROFILE
> +       . = ALIGN(POINTER_ALIGN);
> +       __lock_profile_start = .;
> +       *(.lockprofile.data)
> +       __lock_profile_end = .;
> +#endif
>    } :text
>  
>    . = ALIGN(SMP_CACHE_BYTES);
> @@ -97,13 +104,6 @@ SECTIONS
>         CONSTRUCTORS
>    } :text
>  
> -#ifdef LOCK_PROFILE
> -  . = ALIGN(32);
> -  __lock_profile_start = .;
> -  .lockprofile.data : { *(.lockprofile.data) } :text
> -  __lock_profile_end = .;
> -#endif
> -
>    . = ALIGN(PAGE_SIZE);             /* Init code and data */
>    __init_begin = .;
>    .init.text : {
> diff --git a/xen/include/asm-arm/config.h b/xen/include/asm-arm/config.h
> index c3a2c30..c0ad469 100644
> --- a/xen/include/asm-arm/config.h
> +++ b/xen/include/asm-arm/config.h
> @@ -15,6 +15,7 @@
>  
>  #define BYTES_PER_LONG (1 << LONG_BYTEORDER)
>  #define BITS_PER_LONG (BYTES_PER_LONG << 3)
> +#define POINTER_ALIGN BYTES_PER_LONG
>  
>  /* xen_ulong_t is always 64 bits */
>  #define BITS_PER_XEN_ULONG 64
> diff --git a/xen/include/asm-x86/config.h b/xen/include/asm-x86/config.h
> index 07f3c1f..7291b59 100644
> --- a/xen/include/asm-x86/config.h
> +++ b/xen/include/asm-x86/config.h
> @@ -13,6 +13,7 @@
>  #define BYTES_PER_LONG (1 << LONG_BYTEORDER)
>  #define BITS_PER_LONG (BYTES_PER_LONG << 3)
>  #define BITS_PER_BYTE 8
> +#define POINTER_ALIGN BYTES_PER_LONG
>  
>  #define BITS_PER_XEN_ULONG BITS_PER_LONG
>  
> diff --git a/xen/include/xen/spinlock.h b/xen/include/xen/spinlock.h
> index 77ab7d5..88b53f9 100644
> --- a/xen/include/xen/spinlock.h
> +++ b/xen/include/xen/spinlock.h
> @@ -79,7 +79,7 @@ struct lock_profile_qhead {
>  
>  #define _LOCK_PROFILE(name) { 0, #name, &name, 0, 0, 0, 0, 0 }
>  #define _LOCK_PROFILE_PTR(name)                                              
>  \
> -    static struct lock_profile *__lock_profile_##name                        
>  \
> +    static struct lock_profile * const __lock_profile_##name                 
>  \
>      __used_section(".lockprofile.data") =                                    
>  \
>      &__lock_profile_data_##name
>  #define _SPIN_LOCK_UNLOCKED(x) { { 0 }, SPINLOCK_NO_CPU, 0, _LOCK_DEBUG, x }
> -- 
> 2.1.4
> 

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