Re: [PATCH] Fix possible alignment issue with dw2-dir-file-name test case

[Andreas Arnez <arnez@linux.vnet.ibm.com>]

On Thu, Jan 16 2014, Pedro Alves wrote:

> On 01/15/2014 09:33 PM, Edjunior Barbosa Machado wrote:
>> 
>
>>> testsuite/
>>> 2014-01-10  Andreas Arnez  <arnez@linux.vnet.ibm.com>
>>> 	    Pedro Alves <palves@redhat.com>
>>>
>>> 	* gdb.dwarf2/dw2-dir-file-name.c (FUNC): Remove "*_start" symbol.
>>> 	Make "name" extern.
>>> 	* gdb.dwarf2/dw2-dir-file-name.exp (out_cu, out_line): Replace
>>> 	references to ${name}_start by references to ${name}.
>> 
>> For some reason, the testcase is no longer successful on ppc64 (although it
>> still passes on ppc32): it hits the breakpoints, but no longer shows the
>> filename in none of the tests.
>> 
>> From gdb.log:
>> ...
>> (gdb) break compdir_missing__ldir_missing__file_basename
>> Breakpoint 2 at 0x100006c4
>> (gdb) continue
>> Continuing.
>> 
>> Breakpoint 2, 0x00000000100006c4 in .compdir_missing.ldir_missing.file_basename ()
>
> Bah, looks like the function's low_pc ends up pointing to the function
> descriptor (because that's what the "name" symbol resolves to in the
> debug info in the .S file)?  Looks like we'll need some other solution.

OK, how about this?

----
Subject: [PATCH] Re-introduce '_start' labels and add alignment in dw2-dir-file-name test case.

On ppc64-linux a function symbol does not point to code, but to the
function descriptor.  Thus the previous change for this test case
broke it:

      https://sourceware.org/ml/gdb-patches/2014-01/msg00275.html

This patch reverts to the original method, re-introducing '_start'
symbols.  In addition, it adds sufficient alignment before the label,
such that the label never points into an alignment gap.

testsuite/
2014-01-17  Andreas Arnez  <arnez@linux.vnet.ibm.com>

	* gdb.dwarf2/dw2-dir-file-name.c (FUNC): Insert alignment and
	define "*_start" label.  Make "name" static.

	* gdb.dwarf2/dw2-dir-file-name.exp: Replace references to
	${name} by references to ${name}_start.
---
 gdb/testsuite/gdb.dwarf2/dw2-dir-file-name.c   |   10 +++++++++-
 gdb/testsuite/gdb.dwarf2/dw2-dir-file-name.exp |    6 +++---
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/gdb/testsuite/gdb.dwarf2/dw2-dir-file-name.c b/gdb/testsuite/gdb.dwarf2/dw2-dir-file-name.c
index 2b9cc6a..517df90 100644
--- a/gdb/testsuite/gdb.dwarf2/dw2-dir-file-name.c
+++ b/gdb/testsuite/gdb.dwarf2/dw2-dir-file-name.c
@@ -63,8 +63,16 @@ FUNC (compdir_absolute_ldir_absolute_file_relative_different)	\
 FUNC (compdir_absolute_ldir_absolute_file_absolute_same)	\
 FUNC (compdir_absolute_ldir_absolute_file_absolute_different)
 
+/* Notes: (1) The '*_start' label below is needed because 'name' may
+   point to a function descriptor instead of to the actual code.  (2)
+   The '.balign' should specify the highest possible function
+   alignment across all supported architectures, such that the label
+   never points into the alignment gap.  */
+
 #define FUNC(name)					\
-  void							\
+  asm (".balign 8");					\
+  asm (#name "_start: .globl " #name "_start\n");	\
+  static void						\
   name (void)						\
   {							\
     v++;						\
diff --git a/gdb/testsuite/gdb.dwarf2/dw2-dir-file-name.exp b/gdb/testsuite/gdb.dwarf2/dw2-dir-file-name.exp
index e523e89..7f29581 100644
--- a/gdb/testsuite/gdb.dwarf2/dw2-dir-file-name.exp
+++ b/gdb/testsuite/gdb.dwarf2/dw2-dir-file-name.exp
@@ -54,7 +54,7 @@ proc out_cu { name cu_dir cu_name line_dir line_name } {
 	.ascii	\"GNU C\\0\"			/* DW_AT_producer */
 	.byte	2				/* DW_AT_language (DW_LANG_C) */
 	.4byte	.Lline_${name}_begin		/* DW_AT_stmt_list */
-	.4byte	${name}			/* DW_AT_low_pc */
+	.4byte	${name}_start			/* DW_AT_low_pc */
 	.4byte	${name}_end			/* DW_AT_high_pc */
 "
     if { $cu_dir != "" } {
@@ -65,7 +65,7 @@ proc out_cu { name cu_dir cu_name line_dir line_name } {
 
 	.uleb128	3			/* Abbrev: DW_TAG_subprogram */
 	.asciz		\"${name}\"		/* DW_AT_name */
-	.4byte		${name}		/* DW_AT_low_pc */
+	.4byte		${name}_start		/* DW_AT_low_pc */
 	.4byte		${name}_end		/* DW_AT_high_pc */
 
 	.byte		0			/* End of children of CU */
@@ -122,7 +122,7 @@ proc out_line { name cu_dir cu_name line_dir line_name } {
 	.byte		0	/* DW_LNE_set_address */
 	.uleb128	5
 	.byte		2
-	.4byte		${name}
+	.4byte		${name}_start
 	.byte		1	/* DW_LNS_copy */
 	.byte		3	/* DW_LNS_advance_line */
 	.sleb128	1	/* ... to 1000 */
-- 
1.7.1