1 /* https://bugs.kde.org/show_bug.cgi?id=308626 */ 2 3 #include "../../memcheck.h" 4 5 #include <stdio.h> 6 #include <assert.h> 7 8 typedef unsigned int UInt; 9 10 /* Calculate ctz(x) using bsfl instruction. */ 11 static int ctz(UInt x) 12 { 13 assert(sizeof(UInt) == 4); 14 int result=8*sizeof(UInt); 15 /* BSFL does not change the destination when the input is zero. */ 16 asm("bsfl %1,%0" : "=r" (result) : "r" (x), "0" (result) : "cc"); 17 return result; 18 } 19 20 /* Set the V bits at "addr". Note the convention: A zero bit means 21 "defined"; 1 means "undefined". */ 22 static void set_vbits(UInt *addr, UInt vbits) 23 { 24 (void)VALGRIND_SET_VBITS(addr, &vbits, sizeof(unsigned)); 25 } 26 27 static void doit(unsigned vbits, unsigned val) 28 { 29 /* Since we are about to mark "val" partially undefined, make a 30 copy that we can use without generating a memcheck warning. */ 31 unsigned val_copy = val; 32 33 /* Mark "val" partially undefined. */ 34 set_vbits(&val, vbits); 35 36 /* Convince GCC it does not know what is in "val" so it does not 37 optimize away any uses of it. */ 38 __asm__ ("" : "=r" (val) : "0" (val)); 39 40 int result = ctz(val); 41 42 /* The following code is carefully constructed: The conditional 43 itself should generate a memcheck warning if and only if it is 44 false. (Specifically, if the first "1" bit in val comes before 45 the first "undefined" bit, or the entire word is valid, then 46 ctz(val) is defined; else it is undefined.) */ 47 if (result < ctz(vbits) || vbits == 0) { 48 /* There should be no memcheck warning on this printf, since 49 "result" is fully-defined in this case. */ 50 printf("vbits=0x%08x ctz(0x%08x)=%d\n", vbits, val_copy, result); 51 } 52 else { 53 /* memcheck should have output a warning. But we want 54 something here so there is no possibiliy of Valgrind 55 optimizing out the conditional itself. */ 56 fprintf(stderr, "0x%08x: Invalid value is %d\n", val_copy, 57 ctz(val_copy)); 58 } 59 } 60 61 int main(int argc, char *argv[]) 62 { 63 doit(0x00000000, 0x00000000); 64 doit(0x00000000, 0x00000001); 65 doit(0x00000001, 0x00000000); 66 doit(0x00000001, 0x00000001); 67 68 /* valid bit / data bit sandwich */ 69 doit(0x00000090, 0x00000040); 70 doit(0x00000040, 0x00000090); 71 72 /* Interleaving */ 73 doit(0x00000500, 0x00000a00); 74 doit(0x00000a00, 0x00000500); 75 76 doit(0x000f0000, 0x001e0000); 77 doit(0x001e0000, 0x000f0000); 78 79 doit(0xffffffff, 0xffffffff); 80 doit(0xfffffffe, 0xffffffff); 81 doit(0xffffffff, 0xfffffffe); 82 doit(0xfffffffe, 0xfffffffe); 83 84 return 0; 85 } 86
