[PATCH] Also mark ELF solib trampoline minimal symbols special

["Maciej W. Rozycki" <macro at codesourcery dot com>]

Hi,

 In installing minimal symbols for ELF shared library trampolines we 
"forget" to make individual symbols special where required.  This leads to 
problems on the MIPS target using microMIPS SVR4 lazy stubs.  Lacking the 
special annotation these stubs are treated as standard MIPS code and this 
makes GDB insert the wrong software breakpoint instruction, breaking e.g. 
single-stepping through these stubs.  This is not a very frequent scenario 
as microMIPS SVR4 lazy stubs are typically only used in shared libraries 
with the main executable using PLT, handled elsewhere.  Still it triggers 
e.g. when a software watchpoint has been installed.  The symptom is SIGILL 
or the program going astray, depending on the endianness.  Disassembly of 
these stubs is also wrong.

 Regression-tested with the mips-linux-gnu target and the following 
multilibs:

-EB
-EB -msoft-float
-EB -mips16
-EB -mips16 -msoft-float
-EB -mmicromips
-EB -mmicromips -msoft-float
-EB -mabi=n32
-EB -mabi=n32 -msoft-float
-EB -mabi=64
-EB -mabi=64 -msoft-float

and the -EL variants of same with no regressions and the following 
big-endian failures removed:

(gdb) PASS: gdb.base/watchpoint-solib.exp: rerun to main
continue
Continuing.

Program received signal SIGILL, Illegal instruction.
0x2aad36ab in _dl_sym () at dl-sym.c:282
282	{
(gdb) FAIL: gdb.base/watchpoint-solib.exp: continue to foo again
continue
Continuing.

Program terminated with signal SIGILL, Illegal instruction.
The program no longer exists.
(gdb) FAIL: gdb.base/watchpoint-solib.exp: continue to watchpoint hit again

and similarly for the little endianness:

(gdb) PASS: gdb.base/watchpoint-solib.exp: rerun to main
continue
Continuing.
FAIL: gdb.base/watchpoint-solib.exp: continue to foo again (timeout)
continue
FAIL: gdb.base/watchpoint-solib.exp: continue to watchpoint hit again (timeout)

-- across the -mmicromips multilibs.

 OK to apply?

2014-09-17  Maciej W. Rozycki  <macro@codesourcery.com>

	gdb/
	* elfread.c (elf_symtab_read): Also mark solib trampoline minimal 
	symbols special.

  Maciej

gdb-msymbol-solib-trampoline-special.diff
Index: gdb-fsf-trunk-quilt/gdb/elfread.c
===================================================================
--- gdb-fsf-trunk-quilt.orig/gdb/elfread.c	2014-08-23 01:11:20.000000000 +0100
+++ gdb-fsf-trunk-quilt/gdb/elfread.c	2014-09-16 22:56:52.318922758 +0100
@@ -328,7 +328,10 @@ elf_symtab_read (struct objfile *objfile
 	    (sym->name, strlen (sym->name), copy_names,
 	     symaddr, mst_solib_trampoline, sect, objfile);
 	  if (msym != NULL)
-	    msym->filename = filesymname;
+	    {
+	      msym->filename = filesymname;
+	      gdbarch_elf_make_msymbol_special (gdbarch, sym, msym);
+	    }
 	  continue;
 	}