Messages in this thread |  | | Subject | Re: [PATCH] ipc/sem: ensure we left shift a ULL rather than a 32 bit integer | From | Manfred Spraul <> | Date | Sun, 30 Oct 2016 16:33:23 +0100 |
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On 10/28/2016 09:29 PM, Colin Ian King wrote: > On 28/10/16 20:21, Manfred Spraul wrote: >> Hi Colin, >> >> On 10/28/2016 08:11 PM, Colin King wrote: >> [...] >>> --- a/ipc/sem.c >>> +++ b/ipc/sem.c >>> @@ -1839,7 +1839,7 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct >>> sembuf __user *, tsops, >>> max = 0; >>> for (sop = sops; sop < sops + nsops; sop++) { >>> - unsigned long mask = 1 << ((sop->sem_num) % BITS_PER_LONG); >>> + unsigned long mask = 1ULL << ((sop->sem_num) % BITS_PER_LONG); >>> >> Why 1ULL? Is 1UL not sufficient? > For example, 1UL i386 is 32 bits, where as 1ULL is 64. Exactly: on i386, 'unsigned long" is 32 bits. BITS_PER_LONG is 32. Thus with 1UL, the code should be correct. With 1ULL & -Wconversion, gcc would even report a warning: > gcc -m32 -Wall -Wconversion -O1 test.c > test.c: In function ‘main’: > test.c:13:6: warning: conversion to ‘long unsigned int’ from ‘long > long unsigned int’ may alter its value [-Wconversion] > j= 1ULL << k; > ^~~~
test.c: > #include <stdio.h> > #include <stdlib.h> > > int main(int argc, char **argv) > { > unsigned long j; > int i; > > for (i=1;i<argc;i++) { > long k; > > k=atoi(argv[i]); > j= 1ULL << k; > printf("%d: %lu %ld.\n", i, j, k); > } > return 0; > } >
-- Manfred (still thinks "1UL" is what is required)
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