i#2350 rseq: Remove old run-native code

Reverts the now-obsolete run-native approach for an older version of
the restartable sequence ("rseq") feature. That version never made it
to the mainline kernel, and the run-native approach failed to allow
tools to see rseq code.  Reverts most of commits cda88be and 0935136.

Issue: #2350

core/native_exec.c

@@ -74,7 +74,6 @@ native_exec_init(void)
         ASSERT(retstub_end ==
                local_start + MAX_NATIVE_RETSTACK * BACK_FROM_NATIVE_RETSTUB_SIZE);
     });
-    native_exec_os_init();
 }
 
 void

core/optionsx.h

@@ -1618,14 +1618,6 @@ OPTION_DEFAULT(uint, early_inject_location, 4 /* INJECT_LOCATION_LdrDefault */,
     OPTION_DEFAULT(bool, hook_vsyscall, true, "hook vdso vsyscall if possible")
     /* PR 356503: workaround to allow clients to make syscalls */
     OPTION_ALIAS(sysenter_is_int80, hook_vsyscall, false, STATIC, OP_PCACHE_GLOBAL)
-    /* i#2350: we support restartable sequence ("rseq") Linux kernel extensions,
-     * but as they are not in the mainline kernel we need the number to be passed
-     * in.  If left as 0 the support is disabled.
-     * Current support is preliminary: we execute them natively.
-     */
-    /* XXX: I'd prefer -1 to disable but there's no signed option type. */
-    OPTION_DEFAULT(uint, rseq_sysnum, 0,
-                   "system call number for restartable sequences; 0 disables")
 #endif
 #ifdef UNIX
     OPTION_DEFAULT(bool, restart_syscalls, true,

core/os_shared.h

@@ -620,9 +620,6 @@ void
 os_check_new_app_module(dcontext_t *dcontext, app_pc pc);
 #endif
 
-void
-native_exec_os_init(void);
-
 bool
 get_stack_bounds(dcontext_t *dcontext, byte **base, byte **top);
 

core/unix/os.c

@@ -267,12 +267,6 @@ handle_app_mremap(dcontext_t *dcontext, byte *base, size_t size, byte *old_base,
 static void
 handle_app_brk(dcontext_t *dcontext, byte *lowest_brk /*if known*/, byte *old_brk,
                byte *new_brk);
-static void
-restartable_region_init(void);
-static bool
-handle_restartable_region_syscall_pre(dcontext_t *dcontext);
-static void
-handle_restartable_region_syscall_post(dcontext_t *dcontext, bool success);
 #endif
 
 /* full path to our own library, used for execve */
@@ -7553,9 +7547,6 @@ pre_system_call(dcontext_t *dcontext)
 #endif
 
     default: {
-#ifdef LINUX
-        execute_syscall = handle_restartable_region_syscall_pre(dcontext);
-#endif
 #ifdef VMX86_SERVER
         if (is_vmkuw_sysnum(dcontext->sys_num)) {
             execute_syscall = vmkuw_pre_system_call(dcontext);
@@ -8582,9 +8573,6 @@ post_system_call(dcontext_t *dcontext)
 #endif
 
     default:
-#ifdef LINUX
-        handle_restartable_region_syscall_post(dcontext, success);
-#endif
 #ifdef VMX86_SERVER
         if (is_vmkuw_sysnum(sysnum)) {
             vmkuw_post_system_call(dcontext);
@@ -10465,133 +10453,6 @@ __divdi3(int64 dividend, int64 divisor)
  */
 #endif /* X86_32 */
 
-/****************************************************************************
- * Kernel-restartable sequences
- */
-
-#ifdef LINUX
-/* Support for Linux kernel extensions for per-cpu critical regions.
- * Xref https://lwn.net/Articles/649288/
- * Some of this may vary on different kernels.
- * The way it works is that the app tells the kernel the bounds of a
- * code region within which a context switch should restart the code.
- *
- * As these sequences are complex to handle (it would be much simpler
- * if they used existing mechanisms like signals!), we start out by
- * running their code natively.  We assume it is "well-behaved" and
- * we'll get control back.  These code sequences will be invisible to
- * tools: we'll live with the lack of instrumentation for now as a
- * tradeoff for getting correct app execution.
- *
- * Unfortunately we can't easily have a regression test in the main
- * repository as mainstream kernels do not have this feature.
- */
-
-/* We support a syscall of this form, with number DYNAMO_OPTION(rseq_sysnum):
- *   SYSCALL_DEFINE4(rseq, int, op, long, val1, long, val2, long, val3)
- */
-/* Set operation: app_pc start, app_pc end, app_pc restart */
-#    define RSEQ_SET_CRITICAL 1
-/* Get operation: app_pc *start, app_pc *end, app_pc *restart */
-#    define RSEQ_GET_CRITICAL 3
-
-static app_pc app_restart_region_start;
-static app_pc app_restart_region_end;
-
-static void
-restartable_region_init(void)
-{
-    int res;
-    app_pc restart_handler;
-    if (DYNAMO_OPTION(rseq_sysnum) == 0)
-        return;
-    res = dynamorio_syscall(DYNAMO_OPTION(rseq_sysnum), 4, RSEQ_GET_CRITICAL,
-                            &app_restart_region_start, &app_restart_region_end,
-                            &restart_handler);
-    if (res != 0) {
-        ASSERT(res == -ENOSYS);
-        LOG(GLOBAL, LOG_TOP, 1, "No restartable region at init\n");
-        app_restart_region_start = NULL;
-        app_restart_region_end = NULL;
-    } else {
-        LOG(GLOBAL, LOG_TOP, 1, "Restartable region at init: " PFX "-" PFX " @" PFX "\n",
-            app_restart_region_start, app_restart_region_end, restart_handler);
-        if (app_restart_region_start != NULL &&
-            app_restart_region_end > app_restart_region_start) {
-            vmvector_add(native_exec_areas, app_restart_region_start,
-                         app_restart_region_end, NULL);
-        }
-    }
-}
-
-static bool
-handle_restartable_region_syscall_pre(dcontext_t *dcontext)
-{
-    if (DYNAMO_OPTION(rseq_sysnum) == 0 ||
-        dcontext->sys_num != DYNAMO_OPTION(rseq_sysnum))
-        return true;
-    /* We do the work in post */
-    dcontext->sys_param0 = sys_param(dcontext, 0);
-    dcontext->sys_param1 = sys_param(dcontext, 1);
-    dcontext->sys_param2 = sys_param(dcontext, 2);
-    return true;
-}
-
-/* Though there is a race, it is hard to imagine the app executing correctly
- * without first checking the return value of the syscall.  Thus we handle
- * rseq in post and avoid having to emulate the kernel's argument checking.
- */
-static void
-handle_restartable_region_syscall_post(dcontext_t *dcontext, bool success)
-{
-    int op;
-    if (DYNAMO_OPTION(rseq_sysnum) == 0 ||
-        dcontext->sys_num != DYNAMO_OPTION(rseq_sysnum) || !success)
-        return;
-    op = (int)dcontext->sys_param0;
-    if (op == RSEQ_SET_CRITICAL) {
-        app_pc start = (app_pc)dcontext->sys_param1;
-        app_pc end = (app_pc)dcontext->sys_param2;
-        LOG(THREAD, LOG_VMAREAS | LOG_SYSCALLS, 2,
-            "syscall: set rseq region to " PFX "-" PFX "\n", start, end);
-        /* An unlink flush should be good enough: we simply don't support
-         * suddenly setting an rseq region for some fallthrough code after the
-         * syscall.
-         */
-        if (app_restart_region_start != NULL &&
-            app_restart_region_end > app_restart_region_start) {
-            vmvector_remove(native_exec_areas, app_restart_region_start,
-                            app_restart_region_end);
-            /* Flush existing code so it no longer goes native. */
-            flush_fragments_from_region(dcontext, app_restart_region_start,
-                                        app_restart_region_end - app_restart_region_start,
-                                        false /*don't force synchall*/);
-        }
-        SELF_UNPROTECT_DATASEC(DATASEC_RARELY_PROT);
-        app_restart_region_start = start;
-        app_restart_region_end = end;
-        SELF_PROTECT_DATASEC(DATASEC_RARELY_PROT);
-        if (app_restart_region_start != NULL &&
-            app_restart_region_end > app_restart_region_start) {
-            vmvector_add(native_exec_areas, app_restart_region_start,
-                         app_restart_region_end, NULL);
-            /* We have to flush any existing code in the region. */
-            flush_fragments_from_region(dcontext, app_restart_region_start,
-                                        app_restart_region_end - app_restart_region_start,
-                                        false /*don't force synchall*/);
-        }
-    }
-}
-#endif /* LINUX */
-
-void
-native_exec_os_init(void)
-{
-#ifdef LINUX
-    restartable_region_init();
-#endif
-}
-
 /****************************************************************************
  * Tests
  */

core/win32/os.c

@@ -1185,12 +1185,6 @@ d_r_os_init(void)
     os_get_current_dir(cwd, BUFFER_SIZE_ELEMENTS(cwd));
 }
 
-void
-native_exec_os_init(void)
-{
-    /* Nothing yet. */
-}
-
 static void
 print_mem_stats()
 {