utrace: Use PTHREAD_SEIZE instead of PTHREAD_TRACEME

This makes it easier to handle initial ptrace-stops (after
fork/clone/...), because we don't need to distinguish whether SIGSTOP
is from user or from ptrace. Also execve() does not deliver an extra
SIGTRAP, which we would have to handle.

Signed-off-by: Michal Sojka <sojkam1@fel.cvut.cz>

diff --git a/trace/preload.c b/trace/preload.c
index 99dd906..ee97429 100644 (file)
--- a/trace/preload.c
+++ b/trace/preload.c
@@ -32,7 +32,6 @@ static main_t __main__;
 static int __preload_main__(int argc, char **argv, char **envp)
 {
        unsetenv("LD_PRELOAD");
-       ptrace(PTRACE_TRACEME);
        kill(getpid(), SIGSTOP);
 
        return (*__main__)(argc, argv, envp);

diff --git a/trace/trace.c b/trace/trace.c
index cad2d37..9d3cd0a 100644 (file)
--- a/trace/trace.c
+++ b/trace/trace.c
@@ -24,6 +24,12 @@
 #include <string.h>
 #include <syslog.h>
 
+#ifndef PTRACE_EVENT_STOP
+/* PTRACE_EVENT_STOP is defined in linux/ptrace.h, but this header
+ * collides with musl's sys/ptrace.h */
+#define PTRACE_EVENT_STOP 128
+#endif
+
 #include <libubox/uloop.h>
 #include <libubox/blobmsg.h>
 #include <libubox/blobmsg_json.h>
@@ -150,7 +156,10 @@ static void tracer_cb(struct uloop_process *c, int ret)
        struct tracee *tracee = container_of(c, struct tracee, proc);
        int inject_signal = 0;
 
-       if (WIFSTOPPED(ret)) {
+       /* We explicitely check for events in upper 16 bits, because
+        * musl (as opposed to glibc) does not report
+        * PTRACE_EVENT_STOP as WIFSTOPPED */
+       if (WIFSTOPPED(ret) || (ret >> 16)) {
                if (WSTOPSIG(ret) & 0x80) {
                        if (!tracee->in_syscall) {
                                int syscall = ptrace(PTRACE_PEEKUSER, c->pid, reg_syscall_nr);
@@ -175,6 +184,8 @@ static void tracer_cb(struct uloop_process *c, int ret)
                        uloop_process_add(&child->proc);
                        if (debug)
                                fprintf(stderr, "Tracing new child %d\n", child->proc.pid);
+               } else if ((ret >> 16) == PTRACE_EVENT_STOP) {
+                       /* Nothing special to do here */
                } else {
                        inject_signal = WSTOPSIG(ret);
                        if (debug)
@@ -254,18 +265,18 @@ int main(int argc, char **argv, char **envp)
 
        syscall_max = ARRAY_SIZE(syscall_names);
        syscall_count = calloc(syscall_max, sizeof(int));
-       waitpid(child, &status, 0);
+       waitpid(child, &status, WUNTRACED);
        if (!WIFSTOPPED(status)) {
                ERROR("failed to start %s\n", *argv);
                return -1;
        }
 
-       ptrace(PTRACE_SETOPTIONS, child, 0,
+       ptrace(PTRACE_SEIZE, child, 0,
               PTRACE_O_TRACESYSGOOD |
               PTRACE_O_TRACEFORK |
               PTRACE_O_TRACEVFORK |
               PTRACE_O_TRACECLONE);
-       ptrace(PTRACE_SYSCALL, child, 0, 0);
+       ptrace(PTRACE_SYSCALL, child, 0, SIGCONT);
 
        uloop_init();
        tracer.proc.pid = child;