--- a/gdb/alpha-tdep.c	2017-12-14 15:56:48.955960647 +0100
+++ b/gdb/alpha-tdep.c	2017-12-14 15:56:33.751806965 +0100
@@ -766,10 +766,8 @@
    the sequence.  */
 
 static VEC (CORE_ADDR) *
-alpha_deal_with_atomic_sequence (struct regcache *regcache)
+alpha_deal_with_atomic_sequence (struct gdbarch *gdbarch, CORE_ADDR pc)
 {
-  struct gdbarch *gdbarch = get_regcache_arch (regcache);
-  CORE_ADDR pc = regcache_read_pc (regcache);
   CORE_ADDR breaks[2] = {-1, -1};
   CORE_ADDR loc = pc;
   CORE_ADDR closing_insn; /* Instruction that closes the atomic sequence.  */
@@ -1721,12 +1719,17 @@
 alpha_software_single_step (struct regcache *regcache)
 {
   struct gdbarch *gdbarch = get_regcache_arch (regcache);
-  CORE_ADDR pc;
-  VEC (CORE_ADDR) *next_pcs = NULL;
+  CORE_ADDR pc, next_pc;
+  VEC (CORE_ADDR) *next_pcs;
 
   pc = regcache_read_pc (regcache);
+  next_pcs = alpha_deal_with_atomic_sequence (gdbarch, pc);
+  if (next_pcs != NULL)
+    return next_pcs;
+
+  next_pc = alpha_next_pc (regcache, pc);
 
-  VEC_safe_push (CORE_ADDR, next_pcs, alpha_next_pc (regcache, pc));
+  VEC_safe_push (CORE_ADDR, next_pcs, next_pc);
   return next_pcs;
 }
 
@@ -1826,7 +1829,7 @@
   set_gdbarch_cannot_step_breakpoint (gdbarch, 1);
 
   /* Handles single stepping of atomic sequences.  */
-  set_gdbarch_software_single_step (gdbarch, alpha_deal_with_atomic_sequence);
+  set_gdbarch_software_single_step (gdbarch, alpha_software_single_step);
 
   /* Hook in ABI-specific overrides, if they have been registered.  */
   gdbarch_init_osabi (info, gdbarch);
diff --git a/gdb/nat/linux-ptrace.h b/gdb/nat/linux-ptrace.h
index c5b0f14..8354a4d 100644
--- a/gdb/nat/linux-ptrace.h
+++ b/gdb/nat/linux-ptrace.h
@@ -88,6 +88,57 @@ struct buffer;
 #define __WALL          0x40000000 /* Wait for any child.  */
 #endif
 
+/* True if whether a breakpoint/watchpoint triggered can be determined
+   from the si_code of SIGTRAP's siginfo_t (TRAP_BRKPT/TRAP_HWBKPT).
+   That is, if the kernel can tell us whether the thread executed a
+   software breakpoint, we trust it.  The kernel will be determining
+   that from the hardware (e.g., from which exception was raised in
+   the CPU).  Relying on whether a breakpoint is planted in memory at
+   the time the SIGTRAP is processed to determine whether the thread
+   stopped for a software breakpoint can be too late.  E.g., the
+   breakpoint could have been removed since.  Or the thread could have
+   stepped an instruction the size of a breakpoint instruction, and
+   before the stop is processed a breakpoint is inserted at its
+   address.  Getting these wrong is disastrous on decr_pc_after_break
+   architectures.  The moribund location mechanism helps with that
+   somewhat but it is an heuristic, and can well fail.  Getting that
+   information out of the kernel and ultimately out of the CPU is the
+   way to go.  That said, some architecture may get the si_code wrong,
+   and as such we're leaving fallback code in place.  We'll remove
+   this after a while if no problem is reported.  */
+#define USE_SIGTRAP_SIGINFO 1
+
+/* The x86 kernel gets some of the si_code values backwards, like
+   this:
+
+   | what                                     | si_code    |
+   |------------------------------------------+------------|
+   | software breakpoints (int3)              | SI_KERNEL  |
+   | single-steps                             | TRAP_TRACE |
+   | single-stepping a syscall                | TRAP_BRKPT |
+   | user sent SIGTRAP                        | 0          |
+   | exec SIGTRAP (when no PTRACE_EVENT_EXEC) | 0          |
+   | hardware breakpoints/watchpoints         | TRAP_HWBPT |
+
+   That is, it reports SI_KERNEL for software breakpoints (and only
+   for those), and TRAP_BRKPT for single-stepping a syscall...  If the
+   kernel is ever fixed, we'll just have to detect it like we detect
+   optional ptrace features: by forking and debugging ourselves,
+   running to a breakpoint and checking what comes out of
+   siginfo->si_code.
+
+   The generic Linux target code should use GDB_ARCH_TRAP_BRKPT
+   instead of TRAP_BRKPT to abstract out this x86 peculiarity.  */
+#if defined __i386__ || defined __x86_64__
+# define GDB_ARCH_TRAP_BRKPT SI_KERNEL
+#else
+# define GDB_ARCH_TRAP_BRKPT TRAP_BRKPT
+#endif
+
+#ifndef TRAP_HWBKPT
+# define TRAP_HWBKPT 4
+#endif
+
 extern void linux_ptrace_attach_fail_reason (pid_t pid, struct buffer *buffer);