From a00feef713edc4d586fb41da30e40c22ad3641ce Mon Sep 17 00:00:00 2001
From: Justine Tunney <jtunney@gmail.com>
Date: Fri, 21 Jul 2023 17:16:46 -0700
Subject: [PATCH] Support debugging eXecute-only ELF segments

---
 blink/abort.c         | 20 +++++++++++++++-----
 blink/bios.c          |  2 +-
 blink/blink.c         |  3 +++
 blink/blinkenlights.c | 18 +++++++++++-------
 blink/checked.h       |  9 +++++++++
 blink/debug.c         |  6 +++---
 blink/dis.c           |  4 ++--
 blink/machine.h       |  6 ++++--
 blink/memory.c        | 23 +++++++++++++++++++++--
 blink/syscall.c       |  2 ++
 blink/util.h          |  4 +++-
 blink/watch.c         |  2 +-
 12 files changed, 75 insertions(+), 24 deletions(-)

diff --git a/blink/abort.c b/blink/abort.c
index defc46345..3d0dbea66 100644
--- a/blink/abort.c
+++ b/blink/abort.c
@@ -18,20 +18,30 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include <stdlib.h>
 
+#include "blink/assert.h"
+#include "blink/macros.h"
 #include "blink/stats.h"
 #include "blink/util.h"
 
-bool g_exitdontabort;
+static struct AbortHooks {
+  int n;
+  aborthook_f *p[4];
+} g_aborthooks;
+
+void AtAbort(aborthook_f *hook) {
+  unassert(g_aborthooks.n < ARRAYLEN(g_aborthooks.p));
+  g_aborthooks.p[g_aborthooks.n++] = hook;
+}
 
 void Abort(void) {
+  int i;
 #ifndef NDEBUG
   if (FLAG_statistics) {
     PrintStats();
   }
 #endif
-  if (g_exitdontabort) {
-    exit(1);
-  } else {
-    abort();
+  for (i = g_aborthooks.n; i--;) {
+    g_aborthooks.p[i]();
   }
+  abort();
 }
diff --git a/blink/bios.c b/blink/bios.c
index 4b2d1fe38..c03d998d6 100644
--- a/blink/bios.c
+++ b/blink/bios.c
@@ -475,7 +475,7 @@ static void VidyaServiceWriteTeletype(u8 ch) {
 void VidyaServiceSetMode(int mode) {
   int cols, lines;
   vidya = mode;
-  if (LookupAddress(m, 0xB0000)) {
+  if (SpyAddress(m, 0xB0000)) {
     ptyisenabled = true;
     lines = 25;
     switch (mode) {
diff --git a/blink/blink.c b/blink/blink.c
index 89b473277..3dde8b7d4 100644
--- a/blink/blink.c
+++ b/blink/blink.c
@@ -364,6 +364,9 @@ void exit(int status) {
 int main(int argc, char *argv[]) {
   SetupWeb();
   GetStartDir();
+#ifndef NDEBUG
+  AtAbort(PrintStats);
+#endif
 #ifndef DISABLE_STRACE
   setlocale(LC_ALL, "");
 #endif
diff --git a/blink/blinkenlights.c b/blink/blinkenlights.c
index 07d562902..559bf79e6 100644
--- a/blink/blinkenlights.c
+++ b/blink/blinkenlights.c
@@ -664,7 +664,7 @@ static int VirtualBing(i64 v) {
   int rc;
   jmp_buf busted;
   onbusted = &busted;
-  if ((p = (u8 *)LookupAddress(m, v))) {
+  if ((p = SpyAddress(m, v))) {
     if (!setjmp(busted)) {
       rc = kCp437[p[0] & 255];
     } else {
@@ -686,7 +686,7 @@ static int VirtualShadow(i64 v) {
   jmp_buf busted;
   if (IsShadow(v)) return -2;
   onbusted = &busted;
-  if ((p = (char *)LookupAddress(m, (v >> 3) + 0x7fff8000))) {
+  if ((p = (char *)SpyAddress(m, (v >> 3) + 0x7fff8000))) {
     if (!setjmp(busted)) {
       rc = p[0] & 0xff;
     } else {
@@ -954,6 +954,7 @@ void TuiSetup(void) {
     CommonSetup();
     VfsTcgetattr(ttyout, &oldterm);
     atexit(TtyRestore);
+    AtAbort(TtyRestore);
     once = true;
     report = true;
   }
@@ -1870,7 +1871,7 @@ static void DrawFrames(struct Panel *p) {
     }
     ++i;
     if (((m->ss.base + bp) & 0xfff) > 0xff0) break;
-    if (!(r = LookupAddress(m, m->ss.base + bp))) {
+    if (!(r = SpyAddress(m, m->ss.base + bp))) {
       AppendPanel(p, i - framesstart, "CORRUPT FRAME POINTER");
       break;
     }
@@ -1889,7 +1890,7 @@ static void CheckFramePointerImpl(void) {
   lastbp = bp;
   rp = m->ip;
   while (bp) {
-    if (!(r = LookupAddress(m, m->ss.base + bp))) {
+    if (!(r = SpyAddress(m, m->ss.base + bp))) {
       LOGF("corrupt frame: %0*" PRIx64 "", GetAddrHexWidth(), bp);
       ThrowProtectionFault(m);
     }
@@ -2132,8 +2133,8 @@ void Redraw(bool force) {
     ShowHistory();
     return;
   }
-  LookupAddress(m, m->ip);
-  LookupAddress(m, Get64(m->sp));
+  LookupAddress(m, m->ip);         // want page fault
+  LookupAddress(m, Get64(m->sp));  // want page fault
   BEGIN_NO_PAGE_FAULTS;
   start_draw = GetTime();
   execsecs = ToNanoseconds(SubtractTime(start_draw, last_draw)) * 1e-9;
@@ -3679,9 +3680,12 @@ int main(int argc, char *argv[]) {
   struct System *s;
   static struct sigaction sa;
   setlocale(LC_ALL, "");
-  g_exitdontabort = true;
   SetupWeb();
   GetStartDir();
+  AtAbort(PrintStats);
+#ifndef NDEBUG
+  AtAbort(PrintStats);
+#endif
   // Ensure utf-8 is printed correctly on windows, this method
   // has issues(http://stackoverflow.com/a/10884364/4279) but
   // should work for at least windows 7 and newer.
diff --git a/blink/checked.h b/blink/checked.h
index 88cd2951e..8bd9134b7 100644
--- a/blink/checked.h
+++ b/blink/checked.h
@@ -6,9 +6,18 @@
 
 #define __STDC_VERSION_STDCKDINT_H__ 202311L
 
+#if ((defined(__GNUC__) && __GNUC__ >= 5 && !defined(__ICC)) ||           \
+     (defined(__has_builtin) && (__has_builtin(__builtin_add_overflow) && \
+                                 __has_builtin(__builtin_sub_overflow) && \
+                                 __has_builtin(__builtin_mul_overflow))))
 #define ckd_add(res, x, y) __builtin_add_overflow((x), (y), (res))
 #define ckd_sub(res, x, y) __builtin_sub_overflow((x), (y), (res))
 #define ckd_mul(res, x, y) __builtin_mul_overflow((x), (y), (res))
+#else
+#define ckd_add(res, x, y) (*(res) = (x) + (y), 0)
+#define ckd_sub(res, x, y) (*(res) = (x) - (y), 0)
+#define ckd_mul(res, x, y) (*(res) = (x) * (y), 0)
+#endif
 
 #endif /* <stdckdint.h> */
 #endif /* EASYCKDINT_H_ */
diff --git a/blink/debug.c b/blink/debug.c
index 68bfa2502..e5029fcd3 100644
--- a/blink/debug.c
+++ b/blink/debug.c
@@ -136,14 +136,14 @@ int GetInstruction(struct Machine *m, i64 pc, struct XedDecodedInst *x) {
   int i, rc, err;
   u8 copy[15], *toil, *addr;
   BEGIN_NO_PAGE_FAULTS;
-  if ((addr = LookupAddress(m, pc))) {
+  if ((addr = SpyAddress(m, pc))) {
     if ((i = 4096 - (pc & 4095)) >= 15) {
       if (!DecodeInstruction(x, addr, 15, m->mode.omode)) {
         rc = 0;
       } else {
         rc = kMachineDecodeError;
       }
-    } else if ((toil = LookupAddress(m, pc + i))) {
+    } else if ((toil = SpyAddress(m, pc + i))) {
       memcpy(copy, addr, i);
       memcpy(copy + i, toil, 15 - i);
       if (!DecodeInstruction(x, copy, 15, m->mode.omode)) {
@@ -287,7 +287,7 @@ const char *GetBacktrace(struct Machine *m) {
     }
     ++i;
     if (((m->ss.base + bp) & 0xfff) > 0xff0) break;
-    if (!(r = LookupAddress(m, m->ss.base + bp))) {
+    if (!(r = SpyAddress(m, m->ss.base + bp))) {
       APPEND(" [CORRUPT FRAME POINTER]");
       break;
     }
diff --git a/blink/dis.c b/blink/dis.c
index 3488c3728..dd2e4db7e 100644
--- a/blink/dis.c
+++ b/blink/dis.c
@@ -229,14 +229,14 @@ static long DisAppendOpLines(struct Dis *d, struct Machine *m, i64 addr) {
     }
   }
   n = MAX(1, MIN(15, n));
-  if (!(r = LookupAddress(m, addr))) return -1;
+  if (!(r = SpyAddress(m, addr))) return -1;
   k = 0x1000 - (addr & 0xfff);
   if (n <= k) {
     p = (u8 *)r;
   } else {
     p = b;
     memcpy(b, r, k);
-    if ((r = LookupAddress(m, addr + k))) {
+    if ((r = SpyAddress(m, addr + k))) {
       memcpy(b + k, r, n - k);
     } else {
       n = k;
diff --git a/blink/machine.h b/blink/machine.h
index 4c1319f71..b3ea70b61 100644
--- a/blink/machine.h
+++ b/blink/machine.h
@@ -510,6 +510,7 @@ bool HasPageLock(const struct Machine *, i64) nosideeffect;
 void CollectPageLocks(struct Machine *);
 u8 *LookupAddress(struct Machine *, i64);
 u8 *LookupAddress2(struct Machine *, i64, u64, u64);
+u8 *SpyAddress(struct Machine *, i64);
 u8 *Load(struct Machine *, i64, size_t, u8 *);
 u8 *MallocPage(void);
 u8 *RealAddress(struct Machine *, i64);
@@ -806,8 +807,9 @@ void LogCodOp(struct Machine *, const char *);
 #endif
 
 MICRO_OP_SAFE u8 Cpl(struct Machine *m) {
-  return !m->metal ? 3u :
-         m->mode.genmode != XED_GEN_MODE_REAL ? (m->cs.sel & 3u) : 0u;
+  return !m->metal                              ? 3u
+         : m->mode.genmode != XED_GEN_MODE_REAL ? (m->cs.sel & 3u)
+                                                : 0u;
 }
 
 #define BEGIN_NO_PAGE_FAULTS \
diff --git a/blink/memory.c b/blink/memory.c
index 08fac137d..1119aa53e 100644
--- a/blink/memory.c
+++ b/blink/memory.c
@@ -263,8 +263,7 @@ u64 FindPageTableEntry(struct Machine *m, u64 page) {
 u8 *LookupAddress2(struct Machine *m, i64 virt, u64 mask, u64 need) {
   u8 *host;
   u64 entry;
-  if (!m->metal ||
-      m->mode.omode == XED_MODE_LONG ||
+  if (!m->metal || m->mode.omode == XED_MODE_LONG ||
       (m->mode.genmode != XED_GEN_MODE_REAL && (m->system->cr0 & CR0_PG))) {
     if (!(entry = FindPageTableEntry(m, virt & -4096))) {
       return 0;
@@ -307,6 +306,26 @@ flattencalls u8 *GetAddress(struct Machine *m, i64 v) {
   return LookupAddress(m, v);
 }
 
+/**
+ * Translates virtual address into pointer.
+ *
+ * This function bypasses memory protection, since it's used to display
+ * memory in the debugger tui. That's useful, for example, if debugging
+ * programs that specify an eXecute-only program header.
+ *
+ * It's recommended that the caller use:
+ *
+ *     BEGIN_NO_PAGE_FAULTS;
+ *     i64 address = ...;
+ *     u8 *pointer = SpyAddress(m, address);
+ *     END_NO_PAGE_FAULTS;
+ *
+ * When calling this function.
+ */
+u8 *SpyAddress(struct Machine *m, i64 virt) {
+  return LookupAddress2(m, virt, 0, 0);
+}
+
 u8 *ResolveAddress(struct Machine *m, i64 v) {
   u8 *r;
   if ((r = GetAddress(m, v))) return r;
diff --git a/blink/syscall.c b/blink/syscall.c
index 73d0785a8..a4883e57d 100644
--- a/blink/syscall.c
+++ b/blink/syscall.c
@@ -538,9 +538,11 @@ static int SysSpawn(struct Machine *m, u64 flags, u64 stack, u64 ptid, u64 ctid,
   }
   if (((flags & CLONE_PARENT_SETTID_LINUX) &&
        ((ptid & (sizeof(int) - 1)) ||
+        !IsValidMemory(m, ptid, 4, PROT_READ | PROT_WRITE) ||
         !(ptid_ptr = (_Atomic(int) *)LookupAddress(m, ptid)))) ||
       ((flags & CLONE_CHILD_SETTID_LINUX) &&
        ((ctid & (sizeof(int) - 1)) ||
+        !IsValidMemory(m, ctid, 4, PROT_READ | PROT_WRITE) ||
         !(ctid_ptr = (_Atomic(int) *)LookupAddress(m, ctid))))) {
     LOGF("bad clone() ptid / ctid pointers: %#" PRIx64, flags);
     return efault();
diff --git a/blink/util.h b/blink/util.h
index c1d01338a..e85f770c6 100644
--- a/blink/util.h
+++ b/blink/util.h
@@ -10,12 +10,14 @@
 #include "blink/builtin.h"
 #include "blink/types.h"
 
+typedef void aborthook_f(void);
+
 extern int optind_;
 extern char *optarg_;
 extern const short kCp437[256];
-extern bool g_exitdontabort;
 
 _Noreturn void Abort(void);
+void AtAbort(aborthook_f *);
 char *GetStartDir(void);
 int GetOpt(int, char *const[], const char *);
 u64 tpenc(uint32_t);
diff --git a/blink/watch.c b/blink/watch.c
index b39c375cd..e57c42c6d 100644
--- a/blink/watch.c
+++ b/blink/watch.c
@@ -87,7 +87,7 @@ ssize_t IsAtWatchpoint(struct Watchpoints *wps, struct Machine *m) {
     m->ip = oldip;
     // TODO(jart): Handle case of overlapping page boundary.
     // TODO(jart): Possibly track munmap() type cases.
-    if ((r = LookupAddress(m, wps->p[i].addr))) {
+    if ((r = SpyAddress(m, wps->p[i].addr))) {
       w = Read64(r);
       if (!wps->p[i].initialized) {
         wps->p[i].oldvalue = w;