• Tomeu Vizoso's avatar
    lib: Declare loop variable as volatile before setjmp · 3450cba3
    Tomeu Vizoso authored
    The variable used as loop counter in the igt_fixture macro had
    unspecified value from the setjmp(3) man page quoted below. Because of
    that, in certain circumstances and with -O2 and -Os, the initialization
    of that variable would be eliminated and the compiler would complain of
    uninitialized usage. Below can be found a snippet that reproduces the
    problem with GCC 5.3.1 and 4.9.3 and the errors as printed by 5.3.1.
    
    "The compiler may optimize variables into registers, and longjmp() may
    restore the values of other registers in addition to the stack pointer
    and program  counter. Consequently, the values of automatic variables
    are unspecified after a call to longjmp() if they meet all the following
    criteria:
    
    ·  they are local to the function that made the corresponding setjmp(3)
    call;
    
    ·  their values are changed between the calls to setjmp(3) and
    longjmp(); and
    
    ·  they are not declared as volatile."
    
    static void test(void)
    {
    	igt_subtest_group {
    		igt_fixture {
    		}
    
    		igt_subtest("foo") {
    		}
    
    		igt_fixture {
    		}
    	}
    }
    
    In file included from lib/intel_batchbuffer.h:8:0,
                     from lib/drmtest.h:39,
                     from lib/igt.h:27,
                     from tests/kms_addfb_basic.c:28:
    tests/kms_addfb_basic.c: In function 'tiling_tests.isra.0':
    lib/igt_core.h:110:43: warning: '__tmpint245' is used uninitialized in
    this function [-Wuninitialized]
     #define igt_fixture for (int igt_tokencat(__tmpint,__LINE__) = 0; \
                                               ^
    lib/igt_core.h:110:43: note: '__tmpint245' was declared here
     #define igt_fixture for (int igt_tokencat(__tmpint,__LINE__) = 0; \
                                               ^
    lib/igt_core.h:148:31: note: in definition of macro '__igt_tokencat2'
     #define __igt_tokencat2(x, y) x ## y
                                   ^
    lib/igt_core.h:110:30: note: in expansion of macro 'igt_tokencat'
     #define igt_fixture for (int igt_tokencat(__tmpint,__LINE__) = 0; \
                                  ^
    tests/kms_addfb_basic.c:245:3: note: in expansion of macro 'igt_fixture'
       igt_fixture {
    Signed-off-by: 's avatarTomeu Vizoso <tomeu.vizoso@collabora.com>
    Signed-off-by: Daniel Vetter's avatarDaniel Vetter <daniel.vetter@ffwll.ch>
    3450cba3
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