[PATH RFA] Avoid Cannot read 0x20000000 on cygwin GDB

[Pierre Muller <muller at cerbere dot u-strasbg dot fr>]

  Very often I get 
Cannot read memory at 0x2000000 
when I try to do a backtrace in GDB compiled for Cygwin.

  0x20000000 is the address of the minimal symbol  __size_of_stack_reserve__
but the corresponding memory is not commited (at least not
as long as the stack is not allmost full).

  When trying to backtrace on a level where the code is inside a DLL
(for instance the Cygwin DLL) without symbols, and at an adress higher than
0x20000000, the function get_pc_function_start () returns that value.
This comes from the fact that minimal symbols have no size and that one 
has the highest value.

  The code to check for the function prologue then fails because this address
is not valid.

  I don't know if the same kind of trouble can appear on other targets,
but the patch should be harmless in other cases.


ChangeLog entry:

2000-09-12 Pierre Muller <muller@ics.u-strasbg.fr>
   * blockframe.c (get_pc_function_start): return 0 if the minimal symbol
found is not
      inside a section.


Index: blockframe.c
===================================================================
RCS file: /cvs/src/src/gdb/blockframe.c,v
retrieving revision 1.7
diff -b -c -r1.7 blockframe.c
*** blockframe.c	2000/09/01 23:39:11	1.7
--- blockframe.c	2000/09/12 12:51:00
***************
*** 556,561 ****
--- 556,563 ----
    else if ((msymbol = lookup_minimal_symbol_by_pc (pc)) != NULL)
      {
        fstart = SYMBOL_VALUE_ADDRESS (msymbol);
+       if (!find_pc_section (fstart))
+         return 0;
      }
    else
      {


PS: I didn't recieve any reaction to patch 5 and 6 for pascal support!

PPS: I am currently writing hardware watchpoint support for Cygwin via Page
protections,
it basically works except that I get troubles when the page protection is
triggered inside a system DLL code.



Pierre Muller
Institut Charles Sadron
6,rue Boussingault
F 67083 STRASBOURG CEDEX (France)
mailto:muller@ics.u-strasbg.fr
Phone : (33)-3-88-41-40-07  Fax : (33)-3-88-41-40-99