[PATCH v3] linux-user: Implement starttime field in self stat emulation

[Cameron Esfahani]

Instead of always returning 0, return actual starttime.

v3: Fix formatting issues
v2: Use clock_gettime() instead of scanning /proc/self/stat

Signed-off-by: Cameron Esfahani <dirty@apple.com>
---
 linux-user/main.c    | 14 ++++++++++++++
 linux-user/qemu.h    |  3 +++
 linux-user/syscall.c |  3 +++
 3 files changed, 20 insertions(+)

diff --git a/linux-user/main.c b/linux-user/main.c
index 16def5215d..fbc9bcfd5f 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -190,12 +190,26 @@ void stop_all_tasks(void)
 /* Assumes contents are already zeroed.  */
 void init_task_state(TaskState *ts)
 {
+    long ticks_per_sec;
+    struct timespec bt;
+
     ts->used = 1;
     ts->sigaltstack_used = (struct target_sigaltstack) {
         .ss_sp = 0,
         .ss_size = 0,
         .ss_flags = TARGET_SS_DISABLE,
     };
+
+    /* Capture task start time relative to system boot */
+
+    ticks_per_sec = sysconf(_SC_CLK_TCK);
+
+    if ((ticks_per_sec > 0) && !clock_gettime(CLOCK_BOOTTIME, &bt)) {
+        /* start_boottime is expressed in clock ticks */
+        ts->start_boottime = bt.tv_sec * (uint64_t) ticks_per_sec;
+        ts->start_boottime += bt.tv_nsec * (uint64_t) ticks_per_sec /
+                              NANOSECONDS_PER_SECOND;
+    }
 }
 
 CPUArchState *cpu_copy(CPUArchState *env)
diff --git a/linux-user/qemu.h b/linux-user/qemu.h
index 7910ce59cc..106175406a 100644
--- a/linux-user/qemu.h
+++ b/linux-user/qemu.h
@@ -158,6 +158,9 @@ typedef struct TaskState {
 
     /* This thread's sigaltstack, if it has one */
     struct target_sigaltstack sigaltstack_used;
+
+    /* Start time of task after system boot in clock ticks */
+    uint64_t start_boottime;
 } __attribute__((aligned(16))) TaskState;
 
 abi_long do_brk(abi_ulong new_brk);
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 5950222a77..7b3dbc72d4 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -8107,6 +8107,9 @@ static int open_self_stat(void *cpu_env, int fd)
         } else if (i == 3) {
             /* ppid */
             g_string_printf(buf, FMT_pid " ", getppid());
+        } else if (i == 21) {
+            /* starttime */
+            g_string_printf(buf, "%" PRIu64 " ", ts->start_boottime);
         } else if (i == 27) {
             /* stack bottom */
             g_string_printf(buf, TARGET_ABI_FMT_ld " ", ts->info->start_stack);
-- 
2.32.0 (Apple Git-131)