Re: [PATCH v2 8/8] perf record: Directly bail out for compat case
From: Adrian Hunter <adrian.hunter@intel.com>
Date: 2021-06-02 11:18:44
Also in:
linux-perf-users, lkml
On 2/06/21 1:30 pm, Leo Yan wrote:
Since the 64-bit atomicity is not promised in 32-bit perf, directly report the error and bail out for this case. Now only applies on x86_64 and Arm64 platforms. Suggested-by: Adrian Hunter <adrian.hunter@intel.com>
Maybe we can do better for the compat case.
We can assume the upper 32-bits change very seldom,
and always increase. So for the 'read' case:
u64 first, second, last;
u64 mask = (u64)((u32)-1) << 32;
do {
first = READ_ONCE(pc->aux_head);
rmb();
second = READ_ONCE(pc->aux_head);
rmb();
last = READ_ONCE(pc->aux_head);
} while ((first & mask) != (last & mask));
return second;
For the write case, we can cause a fatal error only if the new
tail has non-zero upper 32-bits. That gives up to 4GiB of data
before aborting:
if (tail & mask)
return -1;
smp_mb();
WRITE_ONCE(pc->aux_tail, tail);
quoted hunk ↗ jump to hunk
Signed-off-by: Leo Yan <redacted> --- tools/perf/builtin-record.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+)diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c index 3337b5f93336..f47e298281f7 100644 --- a/tools/perf/builtin-record.c +++ b/tools/perf/builtin-record.c@@ -74,6 +74,7 @@ #include <linux/zalloc.h> #include <linux/bitmap.h> #include <sys/time.h> +#include <sys/utsname.h> struct switch_output { bool enabled;@@ -848,6 +849,22 @@ static int record__mmap_evlist(struct record *rec, opts->auxtrace_sample_mode; char msg[512]; +#ifndef __LP64__ + struct utsname uts; + int ret; + + ret = uname(&uts); + if (ret < 0) + return ret; + + if (!strncmp(uts.machine, "x86_64", 6) || !strncmp(uts.machine, "aarch64", 7) || + !strncmp(uts.machine, "arm64", 5)) { + pr_err("Error, 32-bit perf cannot record from a 64-bit kernel.\n" + "Please use a 64-bit version of perf instead.\n"); + return -ENOTSUP; + } +#endif + if (opts->affinity != PERF_AFFINITY_SYS) cpu__setup_cpunode_map();
_______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel