Re: [PATCH 1/3] uprobes/core: Make instruction tables volatile.

[Ingo Molnar]

* Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx> wrote:

> From: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
> 
> Some versions of gcc spits a warning about the asm operand for test_bit and
> also causes the first long of the instruction table to be output.
> 
> Fix is similar to 7115e3fc on arch/x86/kernel/kprobes.c
> 
> Signed-off-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
> ---
>  arch/x86/kernel/uprobes.c |   61 ++++++++++++++++++++++++---------------------
>  1 files changed, 32 insertions(+), 29 deletions(-)
> 
> diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> index cf2a184..13d616d 100644
> --- a/arch/x86/kernel/uprobes.c
> +++ b/arch/x86/kernel/uprobes.c
> @@ -53,34 +53,12 @@
>  	  (bc##UL << 0xc)|(bd##UL << 0xd)|(be##UL << 0xe)|(bf##UL << 0xf))    \
>  	 << (row % 32))
>  
> -#ifdef CONFIG_X86_64
> -static u32 good_insns_64[256 / 32] = {
> -	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f         */
> -	/*      ----------------------------------------------         */
> -	W(0x00, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0) | /* 00 */
> -	W(0x10, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0) , /* 10 */
> -	W(0x20, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0) | /* 20 */
> -	W(0x30, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0) , /* 30 */
> -	W(0x40, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) | /* 40 */
> -	W(0x50, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 50 */
> -	W(0x60, 0, 0, 0, 1, 1, 1, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0) | /* 60 */
> -	W(0x70, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 70 */
> -	W(0x80, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 80 */
> -	W(0x90, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 90 */
> -	W(0xa0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* a0 */
> -	W(0xb0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* b0 */
> -	W(0xc0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0) | /* c0 */
> -	W(0xd0, 1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* d0 */
> -	W(0xe0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0) | /* e0 */
> -	W(0xf0, 0, 0, 1, 1, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1)   /* f0 */
> -	/*      ----------------------------------------------         */
> -	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f         */
> -};
> -#endif
> -
> -/* Good-instruction tables for 32-bit apps */
> -
> -static u32 good_insns_32[256 / 32] = {
> +/*
> + * Good-instruction tables for 32-bit apps.  This is non-const and volatile
> + * to keep gcc from statically optimizing it out, as variable_test_bit makes
> + * some versions of gcc to think only *(unsigned long*) is used.
> + */
> +static volatile u32 good_insns_32[256 / 32] = {
>  	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f         */
>  	/*      ----------------------------------------------         */
>  	W(0x00, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 0) | /* 00 */
> @@ -104,7 +82,7 @@ static u32 good_insns_32[256 / 32] = {
>  };
>  
>  /* Using this for both 64-bit and 32-bit apps */
> -static u32 good_2byte_insns[256 / 32] = {
> +static volatile u32 good_2byte_insns[256 / 32] = {
>  	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f         */
>  	/*      ----------------------------------------------         */
>  	W(0x00, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1) | /* 00 */
> @@ -127,6 +105,31 @@ static u32 good_2byte_insns[256 / 32] = {
>  	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f         */
>  };
>  
> +#ifdef CONFIG_X86_64
> +/* Good-instruction tables for 64-bit apps */
> +static volatile u32 good_insns_64[256 / 32] = {
> +	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f         */
> +	/*      ----------------------------------------------         */
> +	W(0x00, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0) | /* 00 */
> +	W(0x10, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0) , /* 10 */
> +	W(0x20, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0) | /* 20 */
> +	W(0x30, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0) , /* 30 */
> +	W(0x40, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) | /* 40 */
> +	W(0x50, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 50 */
> +	W(0x60, 0, 0, 0, 1, 1, 1, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0) | /* 60 */
> +	W(0x70, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 70 */
> +	W(0x80, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 80 */
> +	W(0x90, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 90 */
> +	W(0xa0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* a0 */
> +	W(0xb0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* b0 */
> +	W(0xc0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0) | /* c0 */
> +	W(0xd0, 1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* d0 */
> +	W(0xe0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0) | /* e0 */
> +	W(0xf0, 0, 0, 1, 1, 0, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1)   /* f0 */
> +	/*      ----------------------------------------------         */
> +	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f         */
> +};
> +#endif

Hm, why was the table moved around? This makes it hard to see 
whether it's just a single volatile that is added, or something 
more.

Thanks,

	Ingo
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