lttng-ust: backport musl workaround

musl implementation for _SC_NPROCESSORS_CONF is a bit fishy.

[1] https://www.openwall.com/lists/musl/2019/03/15/5

Anyway, we implemented a fallback.

This patch should be gone by next recipe update.

(From OE-Core rev: 5feddda9ac7ea72eac3d5a83251fa023b67aebce)

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

2 files changed, 111 insertions, 0 deletions

diff --git a/meta/recipes-kernel/lttng/lttng-ust/0001-compat-work-around-broken-_SC_NPROCESSORS_CONF-on-MU.patch b/meta/recipes-kernel/lttng/lttng-ust/0001-compat-work-around-broken-_SC_NPROCESSORS_CONF-on-MU.patch
new file mode 100644
index 0000000000..5c4bd36726
--- /dev/null
+++ b/meta/recipes-kernel/lttng/lttng-ust/0001-compat-work-around-broken-_SC_NPROCESSORS_CONF-on-MU.patch
@@ -0,0 +1,109 @@
+From 5de7c318804a7b1edce8562d4891b4c74aac0677 Mon Sep 17 00:00:00 2001
+From: Michael Jeanson <mjeanson@efficios.com>
+Date: Wed, 20 Mar 2019 11:07:35 -0400
+Subject: [PATCH] compat: work around broken _SC_NPROCESSORS_CONF on MUSL libc
+
+On MUSL libc the _SC_NPROCESSORS_CONF sysconf will report the number of
+CPUs allocated to the task based on the affinity mask instead of the
+total number of CPUs configured on the system.
+
+Upstream-Status: Accepted [1] [5de7c318804a7b1edce8562d4891b4c74aac0677]
+[1] https://lists.lttng.org/pipermail/lttng-dev/2019-March/028616.html
+
+Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
+Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+---
+ libringbuffer/smp.c | 66 +++++++++++++++++++++++++++++++++++++++++++++
+ 1 file changed, 66 insertions(+)
+
+diff --git a/libringbuffer/smp.c b/libringbuffer/smp.c
+index 9e7114be..656a75da 100644
+--- a/libringbuffer/smp.c
++++ b/libringbuffer/smp.c
+@@ -2,6 +2,7 @@
+  * libringbuffer/smp.c
+  *
+  * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
++ * Copyright (C) 2019 Michael Jeanson <mjeanson@efficios.com>
+  *
+  * This library is free software; you can redistribute it and/or
+  * modify it under the terms of the GNU Lesser General Public
+@@ -26,6 +27,7 @@
+ 
+ int __num_possible_cpus;
+ 
++#if (defined(__GLIBC__) || defined( __UCLIBC__))
+ void _get_num_possible_cpus(void)
+ {
+        int result;
+@@ -43,3 +45,67 @@ void _get_num_possible_cpus(void)
+                return;
+        __num_possible_cpus = result;
+ }
++
++#else
++
++/*
++ * The MUSL libc implementation of the _SC_NPROCESSORS_CONF sysconf does not
++ * return the number of configured CPUs in the system but relies on the cpu
++ * affinity mask of the current task.
++ *
++ * So instead we use a strategy similar to GLIBC's, counting the cpu
++ * directories in "/sys/devices/system/cpu" and fallback on the value from
++ * sysconf if it fails.
++ */
++
++#include <dirent.h>
++#include <limits.h>
++#include <stdlib.h>
++#include <string.h>
++#include <sys/types.h>
++
++#define __max(a,b) ((a)>(b)?(a):(b))
++
++void _get_num_possible_cpus(void)
++{
++       int result, count = 0;
++       DIR *cpudir;
++       struct dirent *entry;
++
++       cpudir = opendir("/sys/devices/system/cpu");
++       if (cpudir == NULL)
++               goto end;
++
++       /*
++        * Count the number of directories named "cpu" followed by and
++        * integer. This is the same strategy as glibc uses.
++        */
++       while ((entry = readdir(cpudir))) {
++               if (entry->d_type == DT_DIR &&
++                       strncmp(entry->d_name, "cpu", 3) == 0) {
++
++                       char *endptr;
++                       unsigned long cpu_num;
++
++                       cpu_num = strtoul(entry->d_name + 3, &endptr, 10);
++                       if ((cpu_num < ULONG_MAX) && (endptr != entry->d_name + 3)
++                                       && (*endptr == '\0')) {
++                               count++;
++                       }
++               }
++       }
++
++end:
++       /*
++        * Get the sysconf value as a fallback. Keep the highest number.
++        */
++       result = __max(sysconf(_SC_NPROCESSORS_CONF), count);
++
++       /*
++        * If both methods failed, don't store the value.
++        */
++       if (result < 1)
++               return;
++       __num_possible_cpus = result;
++}
++#endif
+-- 
+2.17.1
+
diff --git a/meta/recipes-kernel/lttng/lttng-ust_2.10.3.bb b/meta/recipes-kernel/lttng/lttng-ust_2.10.3.bb
index c0f408eeec..d546104129 100644
--- a/meta/recipes-kernel/lttng/lttng-ust_2.10.3.bb
+++ b/meta/recipes-kernel/lttng/lttng-ust_2.10.3.bb
@@ -27,7 +27,9 @@ PE = "2"
 
 SRC_URI = "https://lttng.org/files/lttng-ust/lttng-ust-${PV}.tar.bz2 \
            file://lttng-ust-doc-examples-disable.patch \
+           file://0001-compat-work-around-broken-_SC_NPROCESSORS_CONF-on-MU.patch \
           "
+
 SRC_URI[md5sum] = "ffcfa8c1ba9a52f002d240e936e9afa2"
 SRC_URI[sha256sum] = "9e8420f90d5f963f7aa32bc6d44adc1e491136f687c69ffb7a3075d33b40852b"