On Wed, 27 Jul 2022, Andreas Rheinhardt wrote:
Swinney, Jonathan:
This patch looks good to me. I would appreciate its merging.
} while (0)
#define PERF_STOP(t) do { \
+ int ret; \
ioctl(sysfd, PERF_EVENT_IOC_DISABLE, 0); \
- read(sysfd, &t, sizeof(t)); \
+ ret = read(sysfd, &t, sizeof(t)); \
+ (void)ret; \
} while (0)
Why do you use this extra variable instead of just casting the return
value of read to void?
Because if I just cast the return value of read to void, it still warns
about it being unused, at least with GCC 9. I believe the rules for "used
vs unused" for variables (where you can cast it to void to mark it as
used) and "must not ignore return value" (-Wunused-result) differ.
Apparently, in order to appease the compiler for a return value to not be
ignored, it either has to be stored or compared.
// Martin
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