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

On 05.01.2018 02:54, Bryce Harrington wrote:
> 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?

By that reasoning, the original patch that I reverted since it caused
endless loops was already good. ;-)

Thanks for taking a look. I just pushed both patches.

> 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
>>
>> -- 
>> cairo mailing list
>> [email protected]
>> https://lists.cairographics.org/mailman/listinfo/cairo


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