[PATCH] Add some error checking to DWARF assembler

[Tom Tromey <tromey@adacore.com>]

I had written a DWARF location expression like

    DW_OP_const1u
    DW_OP_stack_value

... and was surprised to see that the DW_OP_stack_value didn't appear
in the "readelf" output.

The problem here is that DW_OP_const1u requires an operand, but
neither the DWARF assembler nor gas diagnosed this problem.

This patch adds some checking to Dwarf::_location to try to avoid this
in the future.  I removed some existing checks in the name of
normalization; while the new messages are a bit worse (being
one-size-fits-all), I think this doesn't matter hugely, since this
should only be seen for test suite bugs.

gdb/testsuite/ChangeLog
2021-03-18  Tom Tromey  <tromey@adacore.com>

	* lib/dwarf.exp (Dwarf::_check_n): New proc.
	(Dwarf::_location): Use it.
---
 gdb/testsuite/ChangeLog     |  5 +++++
 gdb/testsuite/lib/dwarf.exp | 33 +++++++++++++++++++++++----------
 2 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/gdb/testsuite/lib/dwarf.exp b/gdb/testsuite/lib/dwarf.exp
index f8fbd381810..64b9e263f10 100644
--- a/gdb/testsuite/lib/dwarf.exp
+++ b/gdb/testsuite/lib/dwarf.exp
@@ -890,6 +890,13 @@ namespace eval Dwarf {
 	}
     }
 
+    # Require N arguments for the opcode.
+    proc _check_n {line op n} {
+	if {[llength $line] != $n + 1} {
+	    error "$op requires $n arguments"
+	}
+    }
+
     # This is a miniature assembler for location expressions.  It is
     # suitable for use in the attributes to a DIE.  Its output is
     # prefixed with "=" to make it automatically use DW_FORM_block.
@@ -926,56 +933,68 @@ namespace eval Dwarf {
 
 	    switch -exact -- $opcode {
 		DW_OP_addr {
+		    _check_n $line $opcode 1
 		    _op .${addr_size}byte [lindex $line 1]
 		}
 
 		DW_OP_regx {
+		    _check_n $line $opcode 1
 		    _op .uleb128 [lindex $line 1]
 		}
 
 		DW_OP_pick -
 		DW_OP_const1u -
 		DW_OP_const1s {
+		    _check_n $line $opcode 1
 		    _op .byte [lindex $line 1]
 		}
 
 		DW_OP_const2u -
 		DW_OP_const2s {
+		    _check_n $line $opcode 1
 		    _op .2byte [lindex $line 1]
 		}
 
 		DW_OP_const4u -
 		DW_OP_const4s {
+		    _check_n $line $opcode 1
 		    _op .4byte [lindex $line 1]
 		}
 
 		DW_OP_const8u -
 		DW_OP_const8s {
+		    _check_n $line $opcode 1
 		    _op .8byte [lindex $line 1]
 		}
 
 		DW_OP_constu {
+		    _check_n $line $opcode 1
 		    _op .uleb128 [lindex $line 1]
 		}
 		DW_OP_consts {
+		    _check_n $line $opcode 1
 		    _op .sleb128 [lindex $line 1]
 		}
 
 		DW_OP_plus_uconst {
+		    _check_n $line $opcode 1
 		    _op .uleb128 [lindex $line 1]
 		}
 
 		DW_OP_piece {
+		    _check_n $line $opcode 1
 		    _op .uleb128 [lindex $line 1]
 		}
 
 		DW_OP_bit_piece {
+		    _check_n $line $opcode 2
 		    _op .uleb128 [lindex $line 1]
 		    _op .uleb128 [lindex $line 2]
 		}
 
 		DW_OP_skip -
 		DW_OP_bra {
+		    _check_n $line $opcode 1
 		    _op .2byte [lindex $line 1]
 		}
 
@@ -1000,9 +1019,7 @@ namespace eval Dwarf {
 
 		DW_OP_implicit_pointer -
 		DW_OP_GNU_implicit_pointer {
-		    if {[llength $line] != 3} {
-			error "usage: $opcode LABEL OFFSET"
-		    }
+		    _check_n $line $opcode 2
 
 		    # Here label is a section offset.
 		    set label [lindex $line 1]
@@ -1015,9 +1032,7 @@ namespace eval Dwarf {
 		}
 
 		DW_OP_GNU_variable_value {
-		    if {[llength $line] != 2} {
-			error "usage: $opcode LABEL"
-		    }
+		    _check_n $line $opcode 1
 
 		    # Here label is a section offset.
 		    set label [lindex $line 1]
@@ -1029,14 +1044,12 @@ namespace eval Dwarf {
 		}
 
 		DW_OP_deref_size {
-		    if {[llength $line] != 2} {
-			error "usage: DW_OP_deref_size SIZE"
-		    }
-
+		    _check_n $line $opcode 1
 		    _op .byte [lindex $line 1]
 		}
 
 		DW_OP_bregx {
+		    _check_n $line $opcode 2
 		    _op .uleb128 [lindex $line 1]
 		    _op .sleb128 [lindex $line 2]
 		}
-- 
2.26.2