[PATCH 1/3] Check function is GC'ed

Yao Qi
2014-08-21T08:26:30Z

I see the following fail on arm-none-eabi target,

(gdb) b 24^M
Breakpoint 1 at 0x4: file
../../../../git/gdb/testsuite/gdb.base/break-on-linker-gcd-function.cc,
line 24.^M
(gdb) FAIL: gdb.base/break-on-linker-gcd-function.exp: b 24

Currently, we are using flag has_section_at_zero to determine whether
address zero in debug info means the corresponding code has been
GC'ed, like this:

case DW_LNE_set_address:
address = read_address (abfd, line_ptr, cu, &bytes_read);

if (address == 0 && !dwarf2_per_objfile->has_section_at_zero)
{
/* This line table is for a function which has been
GCd by the linker. Ignore it. PR gdb/12528 */

However, this is incorrect on some bare metal targets, as .text
section is located at 0x0, so dwarf2_per_objfile->has_section_at_zero
is true. If a function is GC'ed by linker, the address is zero. GDB
thinks address zero is a function's address rather than this function
is GC'ed.

In this patch, we choose 'textlow' field of partial symtabl to check
whether 'textlow' is zero. If it isn't, address zero really means the
function is GC'ed. This patch fixes the fail above. Note that this
patch only fixes the problem on the path that partial symtab is used.
On other paths partial symtab isn't used (start gdb with --readnow for
example), I don't find a good way to fix it.

It is regression tested on x86_64-linux, arm-none-eabi,
arm-none-linux-gnueabi. OK to apply?

gdb:

2014-08-20 Yao Qi <yao@codesourcery.com>

* dwarf2read.c (dwarf_decode_lines_1): Skip the line table if
PST->textlow is greater than zero.
---
gdb/dwarf2read.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index b4d53c8..cf2ce76 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -17229,6 +17229,8 @@ dwarf_decode_lines_1 (struct line_header *lh, const char *comp_dir,
/* Decode the table. */
while (!end_sequence)
{
+ struct partial_symtab *pst = NULL;
+
op_code = read_1_byte (abfd, line_ptr);
line_ptr += 1;
if (line_ptr > line_end)
@@ -17291,7 +17293,12 @@ dwarf_decode_lines_1 (struct line_header *lh, const char *comp_dir,
case DW_LNE_set_address:
address = read_address (abfd, line_ptr, cu, &bytes_read);

- if (address == 0 && !dwarf2_per_objfile->has_section_at_zero)
+ if (!decode_for_pst_p && !dwarf2_per_objfile->using_index)
+ pst = cu->per_cu->v.psymtab;
+
+ if (address == 0
+ && (!dwarf2_per_objfile->has_section_at_zero
+ || (pst != NULL && pst->textlow > address)))
{
/* This line table is for a function which has been
GCd by the linker. Ignore it. PR gdb/12528 */
--
1.9.3