[PATCH v3 3/3] pmu: handle sysconf(_SC_PAGESIZE) negative return value

[Morten Brørup]

Coverity reports some defects, where the root cause seems to be negative
return value from sysconf(_SC_PAGESIZE) not being handled.

The PMU library cannot use the EAL function rte_mem_page_size(), because
of the dependency chain. (EAL depends on PMU, because Trace is part of
EAL, and Trace depends on PMU; so PMU cannot call EAL functions.)
So mem_page_size(), inspired by rte_mem_page_size(), was added to PMU, and
used instead.

Signed-off-by: Morten Brørup <m...@smartsharesystems.com>
Acked-by: Anatoly Burakov <anatoly.bura...@intel.com>
---
 lib/pmu/pmu.c | 32 ++++++++++++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/lib/pmu/pmu.c b/lib/pmu/pmu.c
index 46b0b450ac..4c7271522a 100644
--- a/lib/pmu/pmu.c
+++ b/lib/pmu/pmu.c
@@ -212,14 +212,40 @@ open_events(struct rte_pmu_event_group *group)
        return ret;
 }
 
+/* Inspired by rte_mem_page_size() from /lib/eal/unix/eal_unix_memory.c */
+static size_t
+mem_page_size(void)
+{
+       static size_t page_size;
+
+       if (unlikely(page_size == 0)) {
+               /*
+                * When the sysconf value cannot be determined, sysconf()
+                * returns -1 without setting errno.
+                * To distinguish an indeterminate value from an error,
+                * clear errno before calling sysconf(), and check whether
+                * errno has been set if sysconf() returns -1.
+                */
+               errno = 0;
+               page_size = sysconf(_SC_PAGESIZE);
+               if ((ssize_t)page_size < 0 && errno == 0)
+                       errno = ENOENT;
+       }
+
+       return page_size;
+}
+
 static int
 mmap_events(struct rte_pmu_event_group *group)
 {
-       long page_size = sysconf(_SC_PAGE_SIZE);
+       size_t page_size = mem_page_size();
        unsigned int i;
        void *addr;
        int ret;
 
+       if ((ssize_t)page_size < 0)
+               return -errno;
+
        for (i = 0; i < rte_pmu.num_group_events; i++) {
                addr = mmap(0, page_size, PROT_READ, MAP_SHARED, group->fds[i], 
0);
                if (addr == MAP_FAILED) {
@@ -243,6 +269,7 @@ mmap_events(struct rte_pmu_event_group *group)
 static void
 cleanup_events(struct rte_pmu_event_group *group)
 {
+       size_t page_size = mem_page_size();
        unsigned int i;
 
        if (group->fds[0] != -1)
@@ -250,7 +277,8 @@ cleanup_events(struct rte_pmu_event_group *group)
 
        for (i = 0; i < rte_pmu.num_group_events; i++) {
                if (group->mmap_pages[i]) {
-                       munmap(group->mmap_pages[i], sysconf(_SC_PAGE_SIZE));
+                       __rte_assume((ssize_t)page_size >= 0);
+                       munmap(group->mmap_pages[i], page_size);
                        group->mmap_pages[i] = NULL;
                }
 
-- 
2.43.0