[PATCH 0/6] Use correct function address in dwarf assembler

[Yao Qi <yao@codesourcery.com>]

When we use dwarf assembler, it is common to generate DW_AT_low_pc and
DW_AT_high_pc attributes like this:

 	    subprogram {
		{name main}
		{low_pc main addr}
		{high_pc main+0x100 addr}
            }

however, main is not resolved to function main's address on some
targets such as arm thumb mode and powerpc64.  One approach is to
get function address by labels, like this:

  asm ("func_start: .globl func_start");
  static void func (void) {}
  asm ("func_end: .globl func_end");

however, some compiler, such as clang, can't guarantee the order of
these labels and function, so it isn't portable.

In this patch series, we propose a new approach 

 1. get function start and end address correctly in a portable way,
 2. don't affect too much on existing test cases.

In patch 2/6, a new proc function_range is added.  In this proc, the
source file is compiled with debug info.

  int main (void)
  {
    asm ("main_label: .globl main_label");
    return 0;
  }

we can get the offset of main_label in function main, and then compute
the start address of main via main_label - main_label_offset.  This is
portable.

In order to avoid much changes to existing test cases, we have to use
function_range inside dwarf assembler.  Then, I invent some attribute
macros which look like DW attributes, but can be expanded to one or
more standard attributes.  The TAG_subprogram above will be simplified
with macro attribute used, it becomes:

    subprogram {
	{MACRO_AT_func { func ${srcdir}/${subdir}/${srcfile} }}
    }

With this macro attribute, attributes name, low_pc and high_pc are
generated and set correctly.  See more details in patch 2/6.

Patch 4/6 is to use dwarf assembler to generate .S file, which is
identical to .S current one we are using.  Patch 3 and 5 is to use
macro attributes to get function start and end address correctly.
Patch 6 is remove labels and switch to use macro attribute to
get function start address to make clang happy.

I test the whole series by running tests under gdb.dwarf2/ on
powerpc-linux (both 32-bit and 64-bit), arm-none-eabi (arm mode
and thumb mode) and x86_64-linux.

Comments are very welcome!

*** BLURB HERE ***

Yao Qi (6):
  New proc _handle_attribute
  DW attribute macro MACRO_AT_func and MACRO_AT_range
  Get start and end address of main in dwz.exp
  Use Dwarf::assemble in implptr-optimized-out.exp
  Fix implptr-optimized-out.exp fail
  Fix dw2-ifort-parameter.exp fail with clang

 gdb/testsuite/gdb.dwarf2/dw2-ifort-parameter.c     |   7 +-
 gdb/testsuite/gdb.dwarf2/dw2-ifort-parameter.exp   |   8 +-
 gdb/testsuite/gdb.dwarf2/dwz.exp                   |  60 +-------
 gdb/testsuite/gdb.dwarf2/implptr-optimized-out.S   | 166 ---------------------
 gdb/testsuite/gdb.dwarf2/implptr-optimized-out.exp |  63 +++++++-
 gdb/testsuite/gdb.dwarf2/main.c                    |   1 +
 gdb/testsuite/lib/dwarf.exp                        | 143 ++++++++++++++++--
 7 files changed, 201 insertions(+), 247 deletions(-)
 delete mode 100644 gdb/testsuite/gdb.dwarf2/implptr-optimized-out.S

-- 
1.9.3