Fix for PR tdep/16397: SystemTap SDT probe support for x86 doesn't work with "triplet operands"

This is the continuation of what Joel proposed on:

<https://sourceware.org/ml/gdb-patches/2013-12/msg00977.html>

Now that I have already submitted and pushed the patch to split
i386_stap_parse_special_token into two smaller functions, it is indeed
simpler to understand this patch.

It occurs because, on x86, triplet displacement operands are allowed
(like "-4+8-20(%rbp)"), and the current parser for this expression is
buggy.  It does not correctly extract the register name from the
expression, which leads to incorrect evaluation.  The parser was also
being very "generous" with the expression, so I included a few more
checks to ensure that we're indeed dealing with a triplet displacement
operand.

This patch also includes testcases for the two different kind of
expressions that can be encountered on x86: the triplet displacement
(explained above) and the three-argument displacement (as in
"(%rbx,%ebx,-8)").  The tests are obviously arch-dependent and are
placed under gdb.arch/.

Message-ID: <m3mwj1j12v.fsf@redhat.com>
URL: <https://sourceware.org/ml/gdb-patches/2014-01/msg00310.html>

gdb/
2014-02-20  Sergio Durigan Junior  <sergiodj@redhat.com>

	PR tdep/16397
	* i386-tdep.c (i386_stap_parse_special_token_triplet): Check if a
	number comes after the + or - signs.  Adjust length of register
	name to be extracted.

gdb/testsuite/
2014-02-20  Sergio Durigan Junior  <sergiodj@redhat.com>

	PR tdep/16397
	* gdb.arch/amd64-stap-special-operands.exp: New file.
	* gdb.arch/amd64-stap-three-arg-disp.S: Likewise.
	* gdb.arch/amd64-stap-three-arg-disp.c: Likewise.
	* gdb.arch/amd64-stap-triplet.S: Likewise.
	* gdb.arch/amd64-stap-triplet.c: Likewise.

1 files changed, 10 insertions, 1 deletions

diff --git a/gdb/i386-tdep.c b/gdb/i386-tdep.c
index 57f18cb..bb414b6 100644
--- a/gdb/i386-tdep.c
+++ b/gdb/i386-tdep.c
@@ -3694,6 +3694,9 @@ i386_stap_parse_special_token_triplet (struct gdbarch *gdbarch,
 	  got_minus[0] = 1;
 	}
 
+      if (!isdigit ((unsigned char) *s))
+	return 0;
+
       displacements[0] = strtol (s, &endp, 10);
       s = endp;
 
@@ -3712,6 +3715,9 @@ i386_stap_parse_special_token_triplet (struct gdbarch *gdbarch,
 	  got_minus[1] = 1;
 	}
 
+      if (!isdigit ((unsigned char) *s))
+	return 0;
+
       displacements[1] = strtol (s, &endp, 10);
       s = endp;
 
@@ -3730,6 +3736,9 @@ i386_stap_parse_special_token_triplet (struct gdbarch *gdbarch,
 	  got_minus[2] = 1;
 	}
 
+      if (!isdigit ((unsigned char) *s))
+	return 0;
+
       displacements[2] = strtol (s, &endp, 10);
       s = endp;
 
@@ -3745,7 +3754,7 @@ i386_stap_parse_special_token_triplet (struct gdbarch *gdbarch,
       if (*s++ != ')')
 	return 0;
 
-      len = s - start;
+      len = s - start - 1;
       regname = alloca (len + 1);
 
       strncpy (regname, start, len);