[PATCH][gdb/symtab] Handle gas-generated stabs with -fPIE/-pie

[Tom de Vries <tdevries@suse.de>]

Hi,

With gdb.dwarf2/dw2-ranges.exp and target board unix/-fPIE/-pie, we run into:
...
info line main3^M
No line number information available for address 0x55555555464c <main3>^M
(gdb) FAIL: gdb.dwarf2/dw2-ranges.exp: info line main3
...

The main3 function in the executable comes from dw2-ranges3.o, which is
generated like this (leaving out -fPIE -pie for clarity):
...
$ gcc -S dw2-ranges3.c
$ gcc dw2-ranges3.s -o dw2-ranges3.o -gstabs
...
So, main3 is described in stabs format, generated by gas.

The difference between gcc-generated and gas-generated SLINE stabs is that gcc
generates a sequence SO (source), FUN (function), SLINE (source line) whereas
gas generates SO, SLINE.

The problem is that the line address relocation handling in process_one_symbol
assumes an order of SO, FUN, SLINE.

Fix this by also handling SO, SLINE.

This also fixes FAILs in gdb.btrace/instruction_history.exp with
target board stabs/-fPIE/-pie.

Tested on x86_64-linux with target boards unix, unix/-fPIE/-pie, stabs, and
stabs/-fPIE/-pie.

OK for trunk?

Thanks,
- Tom

[gdb/symtab] Handle gas-generated stabs with -fPIE/-pie

gdb/ChangeLog:

2019-08-16  Tom de Vries  <tdevries@suse.de>

	PR symtab/12497
	* dbxread.c (process_one_symbol): Handle relocation of SLINE address
	without preceding FUN/FNAME.

---
 gdb/dbxread.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/gdb/dbxread.c b/gdb/dbxread.c
index e339d1f7ec..e0ab4ec19c 100644
--- a/gdb/dbxread.c
+++ b/gdb/dbxread.c
@@ -2626,6 +2626,9 @@ process_one_symbol (int type, int desc, CORE_ADDR valu, const char *name,
 
       /* Relocate for dynamic loading and for ELF acc
          function-relative symbols.  */
+      if (function_start_offset == 0)
+	function_start_offset
+	  = ANOFFSET (section_offsets, SECT_OFF_TEXT (objfile));
       valu += function_start_offset;
 
       /* GCC 2.95.3 emits the first N_SLINE stab somwehere in the