Re: [PATCH 2/2] fix warning: variable X might be clobbered by 'longjmp'

On Sat, Dec 23, 2017 at 02:16:08PM +0100, Uli Schlachter wrote:
> According to "man setjmp", one possible way to avoid variable clobbering
> is to declare them as volatile. Thus, this commit turns the variables
> that are changed between setjmp() and longjmp() and whose values are
> still needed after setjmp() returned the second time into volatile
> variables.
> 
> The warning in cairo-bentley-ottmann-rectangular.c is worked around by
> not initializing the variable before setjmp(). To be honest, I don't
> understand why the compiler warns here at all since the value of update
> is clearly not used after setjmp()'s second return.
> 
> This commit re-fixes the warnings that were reintroduced in commit
> 82f40285 which reverted b092b63.
> 
> Signed-off-by: Uli Schlachter <[email protected]>

I don't know all the intricacies of volatile and setjmp(), but trust if
it quells the compiler warning it must be good, right?

Acked-by: Bryce Harrington <[email protected]>

> ---
>  src/cairo-bentley-ottmann-rectangular.c | 4 +++-
>  src/cairo-png.c                         | 6 +++---
>  2 files changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/src/cairo-bentley-ottmann-rectangular.c b/src/cairo-bentley-ottmann-rectangular.c
> index 29f902c1a..65f95d797 100644
> --- a/src/cairo-bentley-ottmann-rectangular.c
> +++ b/src/cairo-bentley-ottmann-rectangular.c
> @@ -603,7 +603,7 @@ _cairo_bentley_ottmann_tessellate_rectangular (rectangle_t	**rectangles,
>      sweep_line_t sweep_line;
>      rectangle_t *rectangle;
>      cairo_status_t status;
> -    cairo_bool_t update = FALSE;
> +    cairo_bool_t update;
>  
>      sweep_line_init (&sweep_line,
>  		     rectangles, num_rectangles,
> @@ -612,6 +612,8 @@ _cairo_bentley_ottmann_tessellate_rectangular (rectangle_t	**rectangles,
>      if ((status = setjmp (sweep_line.unwind)))
>  	return status;
>  
> +    update = FALSE;
> +
>      rectangle = rectangle_pop_start (&sweep_line);
>      do {
>  	if (rectangle->top != sweep_line.current_y) {
> diff --git a/src/cairo-png.c b/src/cairo-png.c
> index 596b506ab..ab0b9d0c5 100644
> --- a/src/cairo-png.c
> +++ b/src/cairo-png.c
> @@ -544,11 +544,11 @@ stream_read_func (png_structp png, png_bytep data, png_size_t size)
>  static cairo_surface_t *
>  read_png (struct png_read_closure_t *png_closure)
>  {
> -    cairo_surface_t *surface;
> +    cairo_surface_t * volatile surface;
>      png_struct *png = NULL;
>      png_info *info;
> -    png_byte *data = NULL;
> -    png_byte **row_pointers = NULL;
> +    png_byte * volatile data = NULL;
> +    png_byte ** volatile row_pointers = NULL;
>      png_uint_32 png_width, png_height;
>      int depth, color_type, interlace, stride;
>      unsigned int i;
> -- 
> 2.15.1
> 
> -- 
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