[PATCH v4 12/13] gdb: Enable signal trampolines in the shadow stack backtrace.

[Christina Schimpe <christina.schimpe@intel.com>]

Similar to the normal backtrace we now print "<signal handler called>"
in the shadow stack backtrace, too.

~~~
(gdb) bt -shadow
/#0  <signal handler called>
/#1  <sigframe token>
/#2  0x00007ffff7c4527e in __GI_raise at ../sysdeps/posix/raise.c:26
/#3  0x0000555555555175 in main at /tmp/gdb.arch/amd64-shadow-stack-signal.c:29
(gdb) bt
/#0  handler (signo=10) at /tmp/amd64-shadow-stack-signal.c:23
/#1  <signal handler called>
/#2  __pthread_kill_implementation (no_tid=0, signo=10, threadid=<optimized out>) at ./nptl/pthread_kill.c:44
/#3  __pthread_kill_internal (signo=10, threadid=<optimized out>) at ./nptl/pthread_kill.c:78
/#4  __GI___pthread_kill (threadid=<optimized out>, signo=signo@entry=10) at ./nptl/pthread_kill.c:89
/#5  0x00007ffff7c4527e in __GI_raise (sig=10) at ../sysdeps/posix/raise.c:26
/#6  0x0000555555555175 in main ()
    at /tmp/amd64-shadow-stack-signal.c:29
~~~
---
 gdb/amd64-linux-tdep.c                        | 36 +++++++++++--------
 gdb/gdbarch-gen.c                             | 32 +++++++++++++++++
 gdb/gdbarch-gen.h                             | 11 ++++++
 gdb/gdbarch_components.py                     | 13 +++++++
 gdb/shadow-stack.c                            | 11 ++++++
 gdb/shadow-stack.h                            |  5 +++
 .../amd64-shadow-stack-backtrace-signal.exp   |  2 +-
 7 files changed, 95 insertions(+), 15 deletions(-)

diff --git a/gdb/amd64-linux-tdep.c b/gdb/amd64-linux-tdep.c
index d98415b8989..ab3b65ed4b8 100644
--- a/gdb/amd64-linux-tdep.c
+++ b/gdb/amd64-linux-tdep.c
@@ -147,12 +147,10 @@ static const gdb_byte amd64_x32_linux_sigtramp_code[] =
    the routine.  Otherwise, return 0.  */
 
 static CORE_ADDR
-amd64_linux_sigtramp_start (const frame_info_ptr &this_frame)
+amd64_linux_sigtramp_start (gdbarch *gdbarch, CORE_ADDR pc)
 {
-  struct gdbarch *gdbarch;
   const gdb_byte *sigtramp_code;
-  CORE_ADDR pc = get_frame_pc (this_frame);
-  gdb_byte buf[LINUX_SIGTRAMP_LEN];
+  std::array<gdb_byte, LINUX_SIGTRAMP_LEN> buf {};
 
   /* We only recognize a signal trampoline if PC is at the start of
      one of the two instructions.  We optimize for finding the PC at
@@ -161,7 +159,7 @@ amd64_linux_sigtramp_start (const frame_info_ptr &this_frame)
      PC is not at the start of the instruction sequence, there will be
      a few trailing readable bytes on the stack.  */
 
-  if (!safe_frame_unwind_memory (this_frame, pc, buf))
+  if (target_read_memory (pc, buf.data (), buf.size ()) != 0)
     return 0;
 
   if (buf[0] != LINUX_SIGTRAMP_INSN0)
@@ -170,28 +168,25 @@ amd64_linux_sigtramp_start (const frame_info_ptr &this_frame)
 	return 0;
 
       pc -= LINUX_SIGTRAMP_OFFSET1;
-      if (!safe_frame_unwind_memory (this_frame, pc, buf))
+      if (target_read_memory (pc, buf.data (), buf.size ()) != 0)
 	return 0;
     }
 
-  gdbarch = get_frame_arch (this_frame);
   if (gdbarch_ptr_bit (gdbarch) == 32)
     sigtramp_code = amd64_x32_linux_sigtramp_code;
   else
     sigtramp_code = amd64_linux_sigtramp_code;
-  if (memcmp (buf, sigtramp_code, LINUX_SIGTRAMP_LEN) != 0)
+  if (memcmp (buf.data (), sigtramp_code, LINUX_SIGTRAMP_LEN) != 0)
     return 0;
 
   return pc;
 }
 
-/* Return whether THIS_FRAME corresponds to a GNU/Linux sigtramp
-   routine.  */
+/* Return whether PC is pointing to a GNU/Linux sigtramp routine.  */
 
 static int
-amd64_linux_sigtramp_p (const frame_info_ptr &this_frame)
+amd64_linux_is_sigtramp_pc (gdbarch* gdbarch, const CORE_ADDR pc)
 {
-  CORE_ADDR pc = get_frame_pc (this_frame);
   const char *name;
 
   find_pc_partial_function (pc, &name, NULL, NULL);
@@ -203,11 +198,22 @@ amd64_linux_sigtramp_p (const frame_info_ptr &this_frame)
      __sigaction, or __libc_sigaction (all aliases to the same
      function).  */
   if (name == NULL || strstr (name, "sigaction") != NULL)
-    return (amd64_linux_sigtramp_start (this_frame) != 0);
+    return (amd64_linux_sigtramp_start (gdbarch, pc) != 0);
 
   return (streq ("__restore_rt", name));
 }
 
+/* Return whether THIS_FRAME corresponds to a GNU/Linux sigtramp
+   routine.  */
+
+static int
+amd64_linux_sigtramp_frame_p (const frame_info_ptr &this_frame)
+{
+  gdbarch *gdbarch = get_frame_arch (this_frame);
+  CORE_ADDR pc = get_frame_pc (this_frame);
+  return amd64_linux_is_sigtramp_pc (gdbarch, pc);
+}
+
 /* Offset to struct sigcontext in ucontext, from <asm/ucontext.h>.  */
 #define AMD64_LINUX_UCONTEXT_SIGCONTEXT_OFFSET 40
 
@@ -2024,7 +2030,7 @@ amd64_linux_init_abi_common (struct gdbarch_info info, struct gdbarch *gdbarch,
 
   linux_init_abi (info, gdbarch, num_disp_step_buffers);
 
-  tdep->sigtramp_p = amd64_linux_sigtramp_p;
+  tdep->sigtramp_p = amd64_linux_sigtramp_frame_p;
   tdep->sigcontext_addr = amd64_linux_sigcontext_addr;
   tdep->sc_reg_offset = amd64_linux_sc_reg_offset;
   tdep->sc_num_regs = ARRAY_SIZE (amd64_linux_sc_reg_offset);
@@ -2082,6 +2088,8 @@ amd64_linux_init_abi_common (struct gdbarch_info info, struct gdbarch *gdbarch,
 
   set_gdbarch_is_no_return_shadow_stack_address
     (gdbarch, amd64_linux_is_no_return_shadow_stack_address);
+
+  set_gdbarch_is_sigtramp_pc (gdbarch, amd64_linux_is_sigtramp_pc);
 }
 
 static void
diff --git a/gdb/gdbarch-gen.c b/gdb/gdbarch-gen.c
index e93afff34b1..c0b882563c1 100644
--- a/gdb/gdbarch-gen.c
+++ b/gdb/gdbarch-gen.c
@@ -257,6 +257,7 @@ struct gdbarch
   gdbarch_top_addr_empty_shadow_stack_ftype *top_addr_empty_shadow_stack = nullptr;
   int shadow_stack_element_size_aligned = 8;
   gdbarch_is_no_return_shadow_stack_address_ftype *is_no_return_shadow_stack_address = nullptr;
+  gdbarch_is_sigtramp_pc_ftype *is_sigtramp_pc = nullptr;
 };
 
 /* Create a new ``struct gdbarch'' based on information provided by
@@ -521,6 +522,7 @@ verify_gdbarch (struct gdbarch *gdbarch)
   /* Skip verify of top_addr_empty_shadow_stack, has predicate.  */
   /* Skip verify of shadow_stack_element_size_aligned, invalid_p == 0.  */
   /* Skip verify of is_no_return_shadow_stack_address, has predicate.  */
+  /* Skip verify of is_sigtramp_pc, has predicate.  */
   if (!log.empty ())
     internal_error (_("verify_gdbarch: the following are invalid ...%s"),
 		    log.c_str ());
@@ -1365,6 +1367,12 @@ gdbarch_dump (struct gdbarch *gdbarch, struct ui_file *file)
   gdb_printf (file,
 	      "gdbarch_dump: is_no_return_shadow_stack_address = <%s>\n",
 	      host_address_to_string (gdbarch->is_no_return_shadow_stack_address));
+  gdb_printf (file,
+	      "gdbarch_dump: gdbarch_is_sigtramp_pc_p() = %d\n",
+	      gdbarch_is_sigtramp_pc_p (gdbarch));
+  gdb_printf (file,
+	      "gdbarch_dump: is_sigtramp_pc = <%s>\n",
+	      host_address_to_string (gdbarch->is_sigtramp_pc));
   if (gdbarch->dump_tdep != nullptr)
     gdbarch->dump_tdep (gdbarch, file);
 }
@@ -5394,3 +5402,27 @@ set_gdbarch_is_no_return_shadow_stack_address (struct gdbarch *gdbarch,
 {
   gdbarch->is_no_return_shadow_stack_address = is_no_return_shadow_stack_address;
 }
+
+bool
+gdbarch_is_sigtramp_pc_p (struct gdbarch *gdbarch)
+{
+  gdb_assert (gdbarch != nullptr);
+  return gdbarch->is_sigtramp_pc != nullptr;
+}
+
+int
+gdbarch_is_sigtramp_pc (struct gdbarch *gdbarch, const CORE_ADDR pc)
+{
+  gdb_assert (gdbarch != nullptr);
+  gdb_assert (gdbarch->is_sigtramp_pc != nullptr);
+  if (gdbarch_debug >= 2)
+    gdb_printf (gdb_stdlog, "gdbarch_is_sigtramp_pc called\n");
+  return gdbarch->is_sigtramp_pc (gdbarch, pc);
+}
+
+void
+set_gdbarch_is_sigtramp_pc (struct gdbarch *gdbarch,
+			    gdbarch_is_sigtramp_pc_ftype is_sigtramp_pc)
+{
+  gdbarch->is_sigtramp_pc = is_sigtramp_pc;
+}
diff --git a/gdb/gdbarch-gen.h b/gdb/gdbarch-gen.h
index 791324777dd..31500ee104d 100644
--- a/gdb/gdbarch-gen.h
+++ b/gdb/gdbarch-gen.h
@@ -1808,3 +1808,14 @@ bool gdbarch_is_no_return_shadow_stack_address_p (struct gdbarch *gdbarch);
 using gdbarch_is_no_return_shadow_stack_address_ftype = std::optional<shadow_stack_frame_info> (struct gdbarch *gdbarch, const CORE_ADDR ssp, const CORE_ADDR value, const unsigned long level);
 std::optional<shadow_stack_frame_info> gdbarch_is_no_return_shadow_stack_address (struct gdbarch *gdbarch, const CORE_ADDR ssp, const CORE_ADDR value, const unsigned long level);
 void set_gdbarch_is_no_return_shadow_stack_address (struct gdbarch *gdbarch, gdbarch_is_no_return_shadow_stack_address_ftype *is_no_return_shadow_stack_address);
+
+/* Return whether PC is pointing to a sigtramp routine.  This is needed in
+   addition to tdep->sigtramp_p, which requires a frame, because some callers
+   (e.g. the shadow stack backtrace command) only have a return address
+   available. */
+
+bool gdbarch_is_sigtramp_pc_p (struct gdbarch *gdbarch);
+
+using gdbarch_is_sigtramp_pc_ftype = int (struct gdbarch *gdbarch, const CORE_ADDR pc);
+int gdbarch_is_sigtramp_pc (struct gdbarch *gdbarch, const CORE_ADDR pc);
+void set_gdbarch_is_sigtramp_pc (struct gdbarch *gdbarch, gdbarch_is_sigtramp_pc_ftype *is_sigtramp_pc);
diff --git a/gdb/gdbarch_components.py b/gdb/gdbarch_components.py
index 0435b1b5eca..fce705c33a1 100644
--- a/gdb/gdbarch_components.py
+++ b/gdb/gdbarch_components.py
@@ -2864,3 +2864,16 @@ backtrace.  Otherwise, return an empty optional.
     ],
     predicate=True,
 )
+
+Method(
+    comment="""
+Return whether PC is pointing to a sigtramp routine.  This is needed in
+addition to tdep->sigtramp_p, which requires a frame, because some callers
+(e.g. the shadow stack backtrace command) only have a return address
+available.
+""",
+    type="int",
+    name="is_sigtramp_pc",
+    params=[("const CORE_ADDR", "pc")],
+    predicate=True,
+)
diff --git a/gdb/shadow-stack.c b/gdb/shadow-stack.c
index 94062034bd3..6515d4b182d 100644
--- a/gdb/shadow-stack.c
+++ b/gdb/shadow-stack.c
@@ -267,6 +267,8 @@ do_print_shadow_stack_frame_info
 	}
       else if (frame.type == ssp_frame_type::dummy_frame)
 	str = "<function called from gdb>";
+      else if (frame.type == ssp_frame_type::sigtramp_frame)
+	str = "<signal handler called>";
       else
 	gdb_assert_not_reached ("Invalid shadow stack frame type.");
 
@@ -480,6 +482,15 @@ get_shadow_stack_frame_info
   if (sal_arch == nullptr)
     sal_arch = fallback_arch;
 
+  if (gdbarch_is_sigtramp_pc_p (sal_arch)
+      && gdbarch_is_sigtramp_pc (sal_arch, value))
+    {
+      return std::optional<shadow_stack_frame_info>
+	({ssp, value, level, sal_arch, sal,
+	  ssp_frame_type::sigtramp_frame, {},
+	  ssp_unwind_stop_reason::no_error});
+    }
+
   return std::optional<shadow_stack_frame_info>
     ({ssp, value, level, sal_arch, sal,
       ssp_frame_type::normal_frame, {},
diff --git a/gdb/shadow-stack.h b/gdb/shadow-stack.h
index 225fd3996cd..d4b0d53acf3 100644
--- a/gdb/shadow-stack.h
+++ b/gdb/shadow-stack.h
@@ -80,6 +80,11 @@ enum class ssp_frame_type
   /* A fake frame, created by GDB when performing an inferior function
      call.  */
   dummy_frame,
+
+  /* A shadow stack frame containing a return address which is in a signal
+     handler, similar to the SIGTRAMP_FRAME frame type in
+     frame.h:frame_type.  */
+  sigtramp_frame,
 };
 
 /* Information of a shadow stack frame belonging to a shadow stack element
diff --git a/gdb/testsuite/gdb.arch/amd64-shadow-stack-backtrace-signal.exp b/gdb/testsuite/gdb.arch/amd64-shadow-stack-backtrace-signal.exp
index 21373dc07f3..34559f0bd04 100644
--- a/gdb/testsuite/gdb.arch/amd64-shadow-stack-backtrace-signal.exp
+++ b/gdb/testsuite/gdb.arch/amd64-shadow-stack-backtrace-signal.exp
@@ -41,7 +41,7 @@ save_vars { ::env(GLIBC_TUNABLES) } {
     # Test shadow stack backtrace including <sigframe token>.
     gdb_test "bt -shadow" \
 	[multi_line \
-	    "#0\[ \t\]*$hex in \[^\r\n\]+" \
+	    "#0\[ \t\]*<signal handler called>" \
 	    "#1\[ \t\]*<sigframe token>" \
 	    "#2\[ \t\]*$hex in \[^\r\n\]+" \
 	    ".*" ] \
-- 
2.34.1

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