Since commit feaf75658783 ("nolibc: fix fd_set type"), an fd_set is an
array of unsigned long, but the FD_* macros still build their masks as
an int or an unsigned int: 1 << n in FD_SET(), 1U << n in FD_CLR() and
FD_ISSET(), where n is the fd modulo 64 on 64-bit architectures. So:
- FD_SET() of an fd with n == 31 sets the bits for n = 31-63, as
1 << 31 is negative and gets sign-extended.
- For n >= 32 the shifts are undefined. x86-64, for instance, masks
the shift count, so FD_SET(40) and FD_ISSET(40) use the bit of fd 8.
- FD_CLR() zero-extends ~(1U << n), so it also clears the bits for
n = 32-63, whichever fd it is given.
select() on fd 40, for instance, fails with EBADF, or watches fd 8
instead if that one is open.
Build the masks from 1UL.
Fixes: feaf75658783 ("nolibc: fix fd_set type")
Cc: [email protected] # v6.2+
Assisted-by: LLM
Signed-off-by: Danish Khateeb <[email protected]>
---
tools/include/nolibc/sys/select.h | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/tools/include/nolibc/sys/select.h
b/tools/include/nolibc/sys/select.h
index 6d65d9ef3d6a..f299c79939f5 100644
--- a/tools/include/nolibc/sys/select.h
+++ b/tools/include/nolibc/sys/select.h
@@ -26,7 +26,7 @@ typedef struct {
int __fd = (fd); \
if (__fd >= 0) \
__set->fds[__fd / FD_SETIDXMASK] &= \
- ~(1U << (__fd & FD_SETBITMASK)); \
+ ~(1UL << (__fd & FD_SETBITMASK)); \
} while (0)
#define FD_SET(fd, set) do { \
@@ -34,7 +34,7 @@ typedef struct {
int __fd = (fd); \
if (__fd >= 0) \
__set->fds[__fd / FD_SETIDXMASK] |= \
- 1 << (__fd & FD_SETBITMASK); \
+ 1UL << (__fd & FD_SETBITMASK); \
} while (0)
#define FD_ISSET(fd, set) ({ \
@@ -43,7 +43,7 @@ typedef struct {
int __r = 0; \
if (__fd >= 0) \
__r = !!(__set->fds[__fd / FD_SETIDXMASK] & \
-1U << (__fd & FD_SETBITMASK)); \
+1UL << (__fd & FD_SETBITMASK));
\
__r; \
})
--
2.55.0
