trace-cmd: Do not make trace-cmd have to build with ptrace

If ptrace is not available on an OS or arch, do not fail the build.
Simply do not support the child tracing feature.

Reported-by: Shawn Bohrer <sbohrer@rgmadvisors.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

3 files changed, 88 insertions, 24 deletions

diff --git a/Makefile b/Makefile
index a3f1dd0..ad717ce 100644
--- a/Makefile
+++ b/Makefile
@@ -13,7 +13,6 @@ FILE_VERSION = 6
 
 MAKEFLAGS += --no-print-directory
 
-
 # Makefiles suck: This macro sets a default value of $(2) for the
 # variable named by $(1), unless the variable has been set by
 # environment or command line. This is necessary for CC and AR
@@ -205,9 +204,22 @@ KERNELSHARK_VERSION = $(KS_VERSION).$(KS_PATCHLEVEL).$(KS_EXTRAVERSION)
 
 INCLUDES = -I. -I/usr/local/include $(CONFIG_INCLUDES)
 
+include features.mk
+
 # Set compile option CFLAGS if not set elsewhere
 CFLAGS ?= -g -Wall
 
+ifndef NO_PTRACE
+ifneq ($(call try-cc,$(SOURCE_PTRACE),),y)
+        NO_PTRACE = 1
+        CFLAGS += -DWARN_NO_PTRACE
+endif
+endif
+
+ifdef NO_PTRACE
+CFLAGS += -DNO_PTRACE
+endif
+
 # Append required CFLAGS
 override CFLAGS += $(CONFIG_FLAGS) $(INCLUDES) $(PLUGIN_DIR_SQ)
 override CFLAGS += $(udis86-flags)
diff --git a/features.mk b/features.mk
new file mode 100644
index 0000000..cb2e8bd
--- /dev/null
+++ b/features.mk
@@ -0,0 +1,36 @@
+
+# taken from perf which was based on Linux Kbuild
+# try-cc
+# Usage: option = $(call try-cc, source-to-build, cc-options)
+try-cc = $(shell sh -c                                                  \
+        'TMP="$(BUILD_OUTPUT)$(TMPOUT).$$$$";                                           \
+        echo "$(1)" |                                                   \
+        $(CC) -x c - $(2) -o "$$TMP" > /dev/null 2>&1 && echo y;        \
+        rm -f "$$TMP"')
+
+define SOURCE_PTRACE
+#include <stdio.h>
+#include <sys/ptrace.h>
+
+int main (void)
+{
+        int ret;
+        ret = ptrace(PTRACE_ATTACH, 0, NULL, 0);
+        ptrace(PTRACE_TRACEME, 0, NULL, 0);
+        ptrace(PTRACE_GETSIGINFO, 0, NULL, NULL);
+        ptrace(PTRACE_GETEVENTMSG, 0, NULL, NULL);
+        ptrace(PTRACE_SETOPTIONS, NULL, NULL,
+                       PTRACE_O_TRACEFORK |
+                       PTRACE_O_TRACEVFORK |
+                       PTRACE_O_TRACECLONE |
+                       PTRACE_O_TRACEEXIT);
+        ptrace(PTRACE_CONT, NULL, NULL, 0);
+        ptrace(PTRACE_DETACH, 0, NULL, NULL);
+        ptrace(PTRACE_SETOPTIONS, 0, NULL,
+               PTRACE_O_TRACEFORK |
+               PTRACE_O_TRACEVFORK |
+               PTRACE_O_TRACECLONE |
+               PTRACE_O_TRACEEXIT);
+        return ret;
+}
+endef
diff --git a/trace-record.c b/trace-record.c
index 45439f4..90589cf 100644
--- a/trace-record.c
+++ b/trace-record.c
@@ -31,7 +31,13 @@
 #include <sys/time.h>
 #include <sys/wait.h>
 #include <sys/socket.h>
+#ifndef NO_PTRACE
 #include <sys/ptrace.h>
+#else
+#ifdef WARN_NO_PTRACE
+#warning ptrace not supported. -c feature will not work
+#endif
+#endif
 #include <netdb.h>
 #include <pthread.h>
 #include <fcntl.h>
@@ -370,6 +376,30 @@ static void
 update_sched_event(struct event_list **event, const char *file,
                    const char *pid_filter, const char *field_filter);
 
+static void update_task_filter(void)
+{
+        int pid = getpid();
+        char spid[100];
+
+        if (!filter_task && filter_pid < 0) {
+                update_ftrace_pid("", 1);
+                enable_tracing();
+                return;
+        }
+
+        if (filter_pid >= 0)
+                pid = filter_pid;
+
+        snprintf(spid, 100, "%d", pid);
+
+        update_ftrace_pid(spid, 1);
+
+        update_pid_event_filters(spid);
+
+        enable_tracing();
+}
+
+#ifndef NO_PTRACE
 static char *make_pid_filter(const char *field)
 {
         struct filter_pids *p;
@@ -430,29 +460,6 @@ static void add_new_filter_pid(int pid)
         free(filter);
 }
 
-static void update_task_filter(void)
-{
-        int pid = getpid();
-        char spid[100];
-
-        if (!filter_task && filter_pid < 0) {
-                update_ftrace_pid("", 1);
-                enable_tracing();
-                return;
-        }
-
-        if (filter_pid >= 0)
-                pid = filter_pid;
-
-        snprintf(spid, 100, "%d", pid);
-
-        update_ftrace_pid(spid, 1);
-
-        update_pid_event_filters(spid);
-
-        enable_tracing();
-}
-
 static void ptrace_attach(int pid)
 {
         int ret;
@@ -529,6 +536,12 @@ static void ptrace_wait(int main_pid)
         } while (!finished && ret > 0 &&
                  (!WIFEXITED(status) || pid != main_pid));
 }
+#else
+static inline void ptrace_wait(int main_pid) { }
+static inline void enable_ptrace(void) { }
+static inline void ptrace_attach(int pid) { }
+
+#endif /* NO_PTRACE */
 
 void trace_or_sleep(void)
 {
@@ -2023,6 +2036,9 @@ void trace_record (int argc, char **argv)
                         filter_pid = atoi(optarg);
                         break;
                 case 'c':
+#ifdef NO_PTRACE
+                        die("-c invalid: ptrace not supported");
+#endif
                         do_ptrace = 1;
                         break;
                 case 'v':