[PATCH v2] linux-user: Implement starttime field in self stat emulation

[Cameron Esfahani]

Instead of always returning 0, return actual starttime.

v2: Use clock_gettime() instead of scanning /proc/self/stat

Signed-off-by: Cameron Esfahani <dirty@apple.com>
---
 linux-user/main.c    | 11 +++++++++++
 linux-user/qemu.h    |  3 +++
 linux-user/syscall.c |  3 +++
 3 files changed, 17 insertions(+)

diff --git a/linux-user/main.c b/linux-user/main.c
index 16def5215d..2e5e0e886b 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -196,6 +196,17 @@ void init_task_state(TaskState *ts)
         .ss_size = 0,
         .ss_flags = TARGET_SS_DISABLE,
     };
+
+    /* Capture task start time relative to system boot */
+
+    long long ticksPerSec = sysconf(_SC_CLK_TCK);
+    struct timespec bt;
+
+    if ((ticksPerSec > 0) && !clock_gettime(CLOCK_BOOTTIME, &bt)) {
+        /* start_boottime is expressed in clock ticks */
+        ts->start_boottime = bt.tv_sec * ticksPerSec;
+        ts->start_boottime += bt.tv_nsec * ticksPerSec / 1000000000L;
+    }
 }
 
 CPUArchState *cpu_copy(CPUArchState *env)
diff --git a/linux-user/qemu.h b/linux-user/qemu.h
index 7910ce59cc..86bc169e72 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 */
+    unsigned long long 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..2f77dbdda7 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, "%llu ", 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)