Fix a few stap parser issues and add a new test for probe expressions

The creation of this patch was motivated by Tom's "Change handling of
'!' operator in stap probes" patch.

While reviewing his patch, I stumbled upon a few issues with the stap
expression parser.  They are:

- As it turns out, even with Tom's patch applied the parser doesn't
  properly handle the '!' operator.  The underlying issue was the fact
  that stap_parse_argument_conditionally also needed to be patched in
  order to recognize '!' as an operator that is part of a single
  operand, and parse it accordingly.

- While writing the testcase I'm proposing on this patch, I found that
  parenthesized sub-expressions were not being parsed correctly when
  there was another term after them.  For example:

    1 - (2 + 3) + 4

  In this case, the parser was considering "1" to be the left-side of
  the expression, and "(2 + 3) + 4" to be the right-side.  The patch
  fixes the parser by making it identify whether a parenthesized
  sub-expression has just been parsed, and act accordingly.

I've tested this on my Debian testing amd64, and everything seems OK.

gdb/ChangeLog:
2021-01-20  Sergio Durigan Junior  <sergiodj@sergiodj.net>
	    Tom Tromey <tom@tromey.com>

	* stap-probe.c (stap_parse_single_operand): Handle '!'
	operator.
	(stap_parse_argument_conditionally): Likewise.
	Skip spaces after processing open-parenthesis sub-expression.
	(stap_parse_argument_1): Skip spaces after call to
	stap_parse_argument_conditionally.
	Handle case when right-side expression is a parenthesized
	sub-expression.
	Skip spaces after call to stap_parse_argument_1.

gdb/testsuite/ChangeLog:
2021-01-20  Sergio Durigan Junior  <sergiodj@sergiodj.net>

	* gdb.arch/amd64-stap-expressions.S: New file.
	* gdb.arch/amd64-stap-expressions.exp: New file.

1 files changed, 26 insertions, 5 deletions

diff --git a/gdb/stap-probe.c b/gdb/stap-probe.c
index c2ddd04..224dd57 100644
--- a/gdb/stap-probe.c
+++ b/gdb/stap-probe.c
@@ -870,7 +870,7 @@ stap_parse_single_operand (struct stap_parse_info *p)
       return;
     }
 
-  if (*p->arg == '-' || *p->arg == '~' || *p->arg == '+')
+  if (*p->arg == '-' || *p->arg == '~' || *p->arg == '+' || *p->arg == '!')
     {
       char c = *p->arg;
       /* We use this variable to do a lookahead.  */
@@ -924,6 +924,8 @@ stap_parse_single_operand (struct stap_parse_info *p)
 	    write_exp_elt_opcode (&p->pstate, UNOP_NEG);
 	  else if (c == '~')
 	    write_exp_elt_opcode (&p->pstate, UNOP_COMPLEMENT);
+	  else if (c == '!')
+	    write_exp_elt_opcode (&p->pstate, UNOP_LOGICAL_NOT);
 	}
     }
   else if (isdigit (*p->arg))
@@ -1012,7 +1014,7 @@ stap_parse_argument_conditionally (struct stap_parse_info *p)
 {
   gdb_assert (gdbarch_stap_is_single_operand_p (p->gdbarch));
 
-  if (*p->arg == '-' || *p->arg == '~' || *p->arg == '+' /* Unary.  */
+  if (*p->arg == '-' || *p->arg == '~' || *p->arg == '+' || *p->arg == '!'
       || isdigit (*p->arg)
       || gdbarch_stap_is_single_operand (p->gdbarch, p->arg))
     stap_parse_single_operand (p);
@@ -1027,11 +1029,12 @@ stap_parse_argument_conditionally (struct stap_parse_info *p)
 
       stap_parse_argument_1 (p, 0, STAP_OPERAND_PREC_NONE);
 
-      --p->inside_paren_p;
+      p->arg = skip_spaces (p->arg);
       if (*p->arg != ')')
-	error (_("Missign close-paren on expression `%s'."),
+	error (_("Missign close-parenthesis on expression `%s'."),
 	       p->saved_arg);
 
+      --p->inside_paren_p;
       ++p->arg;
       if (p->inside_paren_p)
 	p->arg = skip_spaces (p->arg);
@@ -1067,6 +1070,9 @@ stap_parse_argument_1 (struct stap_parse_info *p, bool has_lhs,
       stap_parse_argument_conditionally (p);
     }
 
+  if (p->inside_paren_p)
+    p->arg = skip_spaces (p->arg);
+
   /* Start to parse the right-side, and to "join" left and right sides
      depending on the operation specified.
 
@@ -1104,8 +1110,21 @@ stap_parse_argument_1 (struct stap_parse_info *p, bool has_lhs,
       if (p->inside_paren_p)
 	p->arg = skip_spaces (p->arg);
 
-      /* Parse the right-side of the expression.  */
+      /* Parse the right-side of the expression.
+
+	 We save whether the right-side is a parenthesized
+	 subexpression because, if it is, we will have to finish
+	 processing this part of the expression before continuing.  */
+      bool paren_subexp = *p->arg == '(';
+
       stap_parse_argument_conditionally (p);
+      if (p->inside_paren_p)
+	p->arg = skip_spaces (p->arg);
+      if (paren_subexp)
+	{
+	  write_exp_elt_opcode (&p->pstate, opcode);
+	  continue;
+	}
 
       /* While we still have operators, try to parse another
 	 right-side, but using the current right-side as a left-side.  */
@@ -1130,6 +1149,8 @@ stap_parse_argument_1 (struct stap_parse_info *p, bool has_lhs,
 	  /* Parse the right-side of the expression, but since we already
 	     have a left-side at this point, set `has_lhs' to 1.  */
 	  stap_parse_argument_1 (p, 1, lookahead_prec);
+	  if (p->inside_paren_p)
+	    p->arg = skip_spaces (p->arg);
 	}
 
       write_exp_elt_opcode (&p->pstate, opcode);