Re: [PATCH] sparse: fix bogus shift too big warning when rhs is a variable

[josh@joshtriplett.org]

On Mon, Jun 16, 2014 at 07:10:06PM +0200, Sam Ravnborg wrote:
> From 3e742071e931669108f55b4aae2fb074d1c029cc Mon Sep 17 00:00:00 2001
> From: Sam Ravnborg <sam@ravnborg.org>
> Date: Mon, 16 Jun 2014 19:02:05 +0200
> Subject: [PATCH] sparse: fix bogus shift too big warning when rhs is a
>  variable
> 
> sparse warned about "shift too big" if the rhs was a variable.
> As sparse usually cannot deduct the value of a variable
> silence these warnings.
> 
> Before this patch following code snippet would generate a warning:
> 
> static int doshift(int foo)
> {
> 	return 1 << foo;
> }
> 
> sparse did not know the value of 'foo' so reported a warning.
> Ignore the warning expect in the cases where the rhs of the shift

s/expect/except/

> is a constant.
> 
> Include a few simple tests for left-shift and right-shift.
> 
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

Reviewed-by: Josh Triplett <josh@joshtriplett.org>

Thanks for fixing this!

> ---
>  expand.c                 |  2 +-
>  validation/left-shift.c  | 31 +++++++++++++++++++++++++++++++
>  validation/right-shift.c | 31 +++++++++++++++++++++++++++++++
>  3 files changed, 63 insertions(+), 1 deletion(-)
>  create mode 100644 validation/left-shift.c
>  create mode 100644 validation/right-shift.c
> 
> diff --git a/expand.c b/expand.c
> index 0f6720c..ce955d3 100644
> --- a/expand.c
> +++ b/expand.c
> @@ -187,7 +187,7 @@ static int simplify_int_binop(struct expression *expr, struct symbol *ctype)
>  		return 0;
>  	r = right->value;
>  	if (expr->op == SPECIAL_LEFTSHIFT || expr->op == SPECIAL_RIGHTSHIFT) {
> -		if (r >= ctype->bit_size) {
> +		if (right->flags & Int_const_expr && r >= ctype->bit_size) {
>  			if (conservative)
>  				return 0;
>  			r = check_shift_count(expr, ctype, r);
> diff --git a/validation/left-shift.c b/validation/left-shift.c
> new file mode 100644
> index 0000000..e8d929b
> --- /dev/null
> +++ b/validation/left-shift.c
> @@ -0,0 +1,31 @@
> +static unsigned int leftshift1(unsigned int value, unsigned int shift)
> +{
> +        return 1 << 1000;
> +}
> +
> +static unsigned int leftshift2(unsigned int value, unsigned int shift)
> +{
> +        return value << 1000;
> +}
> +
> +static unsigned int leftshift3(unsigned int value, unsigned int shift)
> +{
> +
> +        return 1 << value;
> +}
> +
> +static unsigned int leftshift4(unsigned int value, unsigned int shift)
> +{
> +
> +        return value << shift;
> +}
> +
> +/*
> + * check-name: Left shift - shift too big
> + *
> + * check-error-start
> +left-shift.c:3:18: warning: shift too big (1000) for type int
> +left-shift.c:8:22: warning: shift too big (1000) for type unsigned int
> + * check-error-end
> + */
> +
> diff --git a/validation/right-shift.c b/validation/right-shift.c
> new file mode 100644
> index 0000000..9be6006
> --- /dev/null
> +++ b/validation/right-shift.c
> @@ -0,0 +1,31 @@
> +static unsigned int rightshift1(unsigned int value, unsigned int shift)
> +{
> +        return 1 >> 1000;
> +}
> +
> +static unsigned int rightshift2(unsigned int value, unsigned int shift)
> +{
> +        return value >> 1000;
> +}
> +
> +static unsigned int rightshift3(unsigned int value, unsigned int shift)
> +{
> +
> +        return 1 >> value;
> +}
> +
> +static unsigned int rightshift4(unsigned int value, unsigned int shift)
> +{
> +
> +        return value >> shift;
> +}
> +
> +/*
> + * check-name: Right shift - shift too big
> + *
> + * check-error-start
> +right-shift.c:3:18: warning: shift too big (1000) for type int
> +right-shift.c:8:22: warning: shift too big (1000) for type unsigned int
> + * check-error-end
> + */
> +
> -- 
> 1.9.3
> 
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