Re: [PATCH] gdb.dwarf2: Define and use gdb_target_symbol_prefix for symbol prefixes

[Kevin Buettner <kevinb at redhat dot com>]

On Fri, 30 Oct 2015 11:06:09 +0000
Pedro Alves <palves@redhat.com> wrote:

> On 10/30/2015 04:25 AM, Kevin Buettner wrote:
> 
> > +# gdb_target_symbol_prefix compiles a test program and uses readelf
> > +# to determine the prefix (such as underscore) for linker symbol
> > +# prefixes.
> > +
> > +proc gdb_target_symbol_prefix {} {
> 
> Shouldn't this be gdb_caching_proc ?

Yes, it should. I've fixed this in my new patch.

> Then T wonder whether something like:
> 
> -                    DW_OP_addr table_2_ptr
> +                    DW_OP_addr [gdb_symbol table_2_ptr]
> 
> instead of prepending the $prefix variable results in clearer
> test code.

I like this idea too. I used the name 'gdb_target_symbol' for this.

Defining the obvious proc (for gdb_target_symbol) worked out of the
box for all cases except gdb.dwarf2/atomic-type.exp.  For that I
needed to make a change to lib/dwarf.exp (and learned a bit more about
tcl in the process).  If you know of a cleaner way to code it, let me
know - I couldn't think of a way to do it without adding the if-else
statement.

> > +	set readelf_program [gdb_find_readelf]
> > +	set result [catch "exec $readelf_program --syms $exe" output]
> > +
> > +	if { $result == 0 \
> > +	     && ![regexp { ([^ a-zA-Z0-9]*)main$} $output dummy prefix] } {
> > +	    verbose "gdb_target_symbol_prefix: Could not find main in readelf output; returning null prefix" 2
> > +	}
> 
> I'm wondering about using a method that would work for mingw/cygwin
> as well.  The only existing use of the target symbol prefix in the
> tree is for those targets, which are coff/pe, not elf.  See
> gdb_target_symbol_prefix_flags.  Maybe just use objdump instead?

I've adjusted my patch to use objdump instead.  This, in turn, helped
me to find a bug with the regexp command that I was using. (By
default, $ doesn't match an end of line, only the end of string.)

With regard to gdb_target_symbol_prefix_flags, I think I'll change
it to call the new gdb_target_symbol_prefix.  That seems preferable
to hardcoding a bunch of targets.  If it all works out, I'll submit a
separate patch.

The new patch is below...

    gdb.dwarf2: Define and use gdb_target_symbol for symbol prefixes
    
    Some of the tests in gdb.dwarf2 which use Dwarf::assemble refer to
    (minimal/linker) symbols created in the course of building a small
    test program.  Some targets use a prefix such as underscore ("_") on
    these symbols.  Many of the tests in gdb.dwarf2 do not take this into
    account.  As a consequence, these tests fail to build, resulting
    either in failures or untested testcases.
    
    Here is an example from gdb.dwarf2/dw2-regno-invalid.exp:
    
        Dwarf::assemble $asm_file {
            cu {} {
                compile_unit {
                    {low_pc main DW_FORM_addr}
                    {high_pc main+0x10000 DW_FORM_addr}
                } {
                ...
                }
    
    For targets which require an underscore prefix on linker symbols,
    the two occurrences of "main" would have to have a prepended underscore,
    i.e. _main instead of main.
    
    For the above case, a call to the new proc gdb_target_symbol is used
    prepend the correct prefix to the symbol.  I.e. the above code is
    rewritten (as shown in the patch) as follows:
    
        Dwarf::assemble $asm_file {
            cu {} {
                compile_unit {
                    {low_pc [gdb_target_symbol main] DW_FORM_addr}
                    {high_pc [gdb_target_symbol main]+0x10000 DW_FORM_addr}
                } {
                ...
                }
    
    I also found it necessary to make an adjustment to lib/dwarf.exp so that
    expressions of more than just one list element can be used in DW_TAG_...
    constructs.  The change to atomic-type.exp was the only change which
    required this new functionality.
    
    gdb/testsuite/ChangeLog:
    
    	* lib/gdb.exp (gdb_target_symbol_prefix, gdb_target_symbol):
    	New procs.
    	* lib/dwarf.exp (_handle_DW_TAG): Handle attribute values,
    	representing expressions, of more than one list element.
    	* gdb.dwarf2/atomic-type.exp (Dwarf::assemble): Use gdb_target_symbol
    	to prepend linker symbol prefix to f.
    	* gdb.dwarf2/data-loc.exp (Dwarf::assemble): Likewise, for
    	table_1 and table_2.
    	* gdb.dwarf2/dw2-bad-mips-linkage-name.exp (Dwarf::assemble):
    	Likewise, for f and g.
    	* gdb.dwarf2/dw2-ifort-parameter.exp (Dwarf::assemble): Likewise,
    	for ptr.
    	* gdb.dwarf2/dw2-regno-invalid.exp (Dwarf::assemble): Likewise,
    	for main.
    	* gdb.dwarf2/dynarr-ptr.exp (Dwarf::assemble): Likewise, for
    	table_1_ptr and table_2_ptr.
---
 gdb/testsuite/gdb.dwarf2/atomic-type.exp           |  2 +-
 gdb/testsuite/gdb.dwarf2/data-loc.exp              |  8 ++--
 .../gdb.dwarf2/dw2-bad-mips-linkage-name.exp       |  4 +-
 gdb/testsuite/gdb.dwarf2/dw2-ifort-parameter.exp   |  2 +-
 gdb/testsuite/gdb.dwarf2/dw2-regno-invalid.exp     |  8 ++--
 gdb/testsuite/gdb.dwarf2/dynarr-ptr.exp            |  8 ++--
 gdb/testsuite/lib/dwarf.exp                        | 15 ++++++-
 gdb/testsuite/lib/gdb.exp                          | 48 ++++++++++++++++++++++
 8 files changed, 77 insertions(+), 18 deletions(-)

diff --git a/gdb/testsuite/gdb.dwarf2/atomic-type.exp b/gdb/testsuite/gdb.dwarf2/atomic-type.exp
index fb315e3..e2a3447 100644
--- a/gdb/testsuite/gdb.dwarf2/atomic-type.exp
+++ b/gdb/testsuite/gdb.dwarf2/atomic-type.exp
@@ -68,7 +68,7 @@ Dwarf::assemble $asm_file {
 
             DW_TAG_subprogram {
                 {name f}
-                {low_pc f addr}
+                {low_pc [gdb_target_symbol f] addr}
                 {high_pc f_end_lbl addr}
                 {type :$i_l}
             } {
diff --git a/gdb/testsuite/gdb.dwarf2/data-loc.exp b/gdb/testsuite/gdb.dwarf2/data-loc.exp
index e9e702c..a1fb772 100644
--- a/gdb/testsuite/gdb.dwarf2/data-loc.exp
+++ b/gdb/testsuite/gdb.dwarf2/data-loc.exp
@@ -84,7 +84,7 @@ Dwarf::assemble $asm_file {
                 {DW_AT_name foo__three}
                 {DW_AT_type :$array_label}
                 {DW_AT_location {
-                    DW_OP_addr table_1
+                    DW_OP_addr [gdb_target_symbol table_1]
                 } SPECIAL_expr}
                 {external 1 flag}
             }
@@ -92,7 +92,7 @@ Dwarf::assemble $asm_file {
                 {DW_AT_name foo__three_tdef}
                 {DW_AT_type :$array_ptr_label}
                 {DW_AT_location {
-                    DW_OP_addr table_1
+                    DW_OP_addr [gdb_target_symbol table_1]
                 } SPECIAL_expr}
                 {external 1 flag}
             }
@@ -100,7 +100,7 @@ Dwarf::assemble $asm_file {
                 {DW_AT_name foo__five}
                 {DW_AT_type :$array_label}
                 {DW_AT_location {
-                    DW_OP_addr table_2
+                    DW_OP_addr [gdb_target_symbol table_2]
                 } SPECIAL_expr}
                 {external 1 flag}
             }
@@ -108,7 +108,7 @@ Dwarf::assemble $asm_file {
                 {DW_AT_name foo__five_tdef}
                 {DW_AT_type :$array_ptr_label}
                 {DW_AT_location {
-                    DW_OP_addr table_2
+                    DW_OP_addr [gdb_target_symbol table_2]
                 } SPECIAL_expr}
                 {external 1 flag}
             }
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-bad-mips-linkage-name.exp b/gdb/testsuite/gdb.dwarf2/dw2-bad-mips-linkage-name.exp
index 77f6175..dfb9567 100644
--- a/gdb/testsuite/gdb.dwarf2/dw2-bad-mips-linkage-name.exp
+++ b/gdb/testsuite/gdb.dwarf2/dw2-bad-mips-linkage-name.exp
@@ -42,14 +42,14 @@ Dwarf::assemble $asm_file {
 	    }
             DW_TAG_subprogram {
                 {name f}
-                {low_pc f addr}
+                {low_pc [gdb_target_symbol f] addr}
                 {high_pc f_end_lbl addr}
                 {type :$b_l}
 		{DW_AT_MIPS_linkage_name _Z1fv}
 	    }
             DW_TAG_subprogram {
                 {name g}
-                {low_pc g addr}
+                {low_pc [gdb_target_symbol g] addr}
                 {high_pc g_end_lbl addr}
                 {type :$b_l}
 		{DW_AT_MIPS_linkage_name 42 DW_FORM_data1}
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-ifort-parameter.exp b/gdb/testsuite/gdb.dwarf2/dw2-ifort-parameter.exp
index c71103d..4f07b50 100644
--- a/gdb/testsuite/gdb.dwarf2/dw2-ifort-parameter.exp
+++ b/gdb/testsuite/gdb.dwarf2/dw2-ifort-parameter.exp
@@ -53,7 +53,7 @@ Dwarf::assemble $asm_file {
 		    {variable_parameter 1 flag}
 		    {type :$int_label}
 		    {location {
-			addr ptr
+			addr [gdb_target_symbol ptr]
 			deref
 		    } SPECIAL_expr}
 		}
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-regno-invalid.exp b/gdb/testsuite/gdb.dwarf2/dw2-regno-invalid.exp
index a7d77c5..53897bd 100644
--- a/gdb/testsuite/gdb.dwarf2/dw2-regno-invalid.exp
+++ b/gdb/testsuite/gdb.dwarf2/dw2-regno-invalid.exp
@@ -29,8 +29,8 @@ set asm_file [standard_output_file $srcfile]
 Dwarf::assemble $asm_file {
     cu {} {
 	compile_unit {
-	    {low_pc main DW_FORM_addr}
-	    {high_pc main+0x10000 DW_FORM_addr}
+	    {low_pc [gdb_target_symbol main] DW_FORM_addr}
+	    {high_pc [gdb_target_symbol main]+0x10000 DW_FORM_addr}
 	} {
 	    declare_labels integer_label
 
@@ -43,8 +43,8 @@ Dwarf::assemble $asm_file {
 	    DW_TAG_subprogram {
 		{name main}
 		{DW_AT_external 1 flag}
-		{low_pc main DW_FORM_addr}
-		{high_pc main+0x10000 DW_FORM_addr}
+		{low_pc [gdb_target_symbol main] DW_FORM_addr}
+		{high_pc [gdb_target_symbol main]+0x10000 DW_FORM_addr}
 	    } {
 		DW_TAG_variable {
 		    {DW_AT_name bregx}
diff --git a/gdb/testsuite/gdb.dwarf2/dynarr-ptr.exp b/gdb/testsuite/gdb.dwarf2/dynarr-ptr.exp
index 3dcb3d7..0a612fe 100644
--- a/gdb/testsuite/gdb.dwarf2/dynarr-ptr.exp
+++ b/gdb/testsuite/gdb.dwarf2/dynarr-ptr.exp
@@ -85,7 +85,7 @@ Dwarf::assemble $asm_file {
                 {DW_AT_name foo__three_ptr}
                 {DW_AT_type :$array_ptr_label}
                 {DW_AT_location {
-                    DW_OP_addr table_1_ptr
+                    DW_OP_addr [gdb_target_symbol table_1_ptr]
                 } SPECIAL_expr}
                 {external 1 flag}
             }
@@ -93,7 +93,7 @@ Dwarf::assemble $asm_file {
                 {DW_AT_name foo__three_ptr_tdef}
                 {DW_AT_type :$array_typedef_label}
                 {DW_AT_location {
-                    DW_OP_addr table_1_ptr
+                    DW_OP_addr [gdb_target_symbol table_1_ptr]
                 } SPECIAL_expr}
                 {external 1 flag}
             }
@@ -101,7 +101,7 @@ Dwarf::assemble $asm_file {
                 {DW_AT_name foo__five_ptr}
                 {DW_AT_type :$array_ptr_label}
                 {DW_AT_location {
-                    DW_OP_addr table_2_ptr
+                    DW_OP_addr [gdb_target_symbol table_2_ptr]
                 } SPECIAL_expr}
                 {external 1 flag}
             }
@@ -109,7 +109,7 @@ Dwarf::assemble $asm_file {
                 {DW_AT_name foo__five_ptr_tdef}
                 {DW_AT_type :$array_typedef_label}
                 {DW_AT_location {
-                    DW_OP_addr table_2_ptr
+                    DW_OP_addr [gdb_target_symbol table_2_ptr]
                 } SPECIAL_expr}
                 {external 1 flag}
             }
diff --git a/gdb/testsuite/lib/dwarf.exp b/gdb/testsuite/lib/dwarf.exp
index 888ba94..eb2e59c 100644
--- a/gdb/testsuite/lib/dwarf.exp
+++ b/gdb/testsuite/lib/dwarf.exp
@@ -621,7 +621,18 @@ namespace eval Dwarf {
 
 	foreach attr $attrs {
 	    set attr_name [_map_name [lindex $attr 0] _AT]
-	    set attr_value [uplevel 2 [list subst [lindex $attr 1]]]
+
+	    # When the length of ATTR is greater than 2, the last element
+	    # of the list must be a form.  The second through the
+	    # penultimate elements are joined together and evaluated
+	    # using subst.  This allows constructs such as
+	    # [gdb_target_symbol foo] to be used.
+
+	    if {[llength $attr] > 2} {
+	        set attr_value [uplevel 2 [list subst [join [lrange $attr 1 end-1]]]]
+	    } {
+	        set attr_value [uplevel 2 [list subst [lindex $attr 1]]]
+	    }
 
 	    if { [string equal "MACRO_AT_func" $attr_name] } {
 		_handle_macro_at_func $attr_value
@@ -629,7 +640,7 @@ namespace eval Dwarf {
 		_handle_macro_at_range $attr_value
 	    } else {
 		if {[llength $attr] > 2} {
-		    set attr_form [lindex $attr 2]
+		    set attr_form [lindex $attr end]
 		} else {
 		    # If the value looks like an integer, a form is required.
 		    if [string is integer $attr_value] {
diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index 048070b..e1c9839 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -5521,6 +5521,54 @@ proc core_find {binfile {deletefiles {}} {arg ""}} {
     return $destcore
 }
 
+# gdb_target_symbol_prefix compiles a test program and uses readelf to
+# determine the prefix (such as underscore) for linker symbol
+# prefixes.
+
+gdb_caching_proc gdb_target_symbol_prefix {
+    # Set up and compile a simple test program...
+    set src [standard_temp_file main[pid].c]
+    set exe [standard_temp_file main[pid].x]
+
+    gdb_produce_source $src {
+	int main() {
+	    return 0;
+	}
+    }
+
+    verbose "compiling testfile $src" 2
+    set compile_flags {debug nowarnings quiet}
+    set lines [gdb_compile $src $exe executable $compile_flags]
+
+    set prefix ""
+
+    if ![string match "" $lines] then {
+        verbose "gdb_target_symbol_prefix: testfile compilation failed, returning null prefix" 2
+    } else {
+	set objdump_program [gdb_find_objdump]
+	set result [catch "exec $objdump_program --syms $exe" output]
+
+	if { $result == 0 \
+	     && ![regexp -lineanchor \
+	          { ([^ a-zA-Z0-9]*)main$} $output dummy prefix] } {
+	    verbose "gdb_target_symbol_prefix: Could not find main in objdump output; returning null prefix" 2
+	}
+    }
+
+    file delete $src
+    file delete $exe
+
+    return $prefix
+}
+
+# gdb_target_symbol returns the provided symbol with the correct prefix
+# prepended.  (See gdb_target_symbol_prefix, above.)
+
+proc gdb_target_symbol { symbol } {
+  set prefix [gdb_target_symbol_prefix]
+  return "${prefix}${symbol}"
+}
+
 # gdb_target_symbol_prefix_flags returns a string that can be added
 # to gdb_compile options to define SYMBOL_PREFIX macro value
 # symbol_prefix_flags returns a string that can be added