[binutils-gdb] [regression] Do not read from catchpoint/watchpoint locations' addresses when checking for a permane

[Luis Machado <luisgpm at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=244558af868d5427903c35c5105bf5499639f81f

commit 244558af868d5427903c35c5105bf5499639f81f
Author: Luis Machado <lgustavo@codesourcery.com>
Date:   Wed Aug 12 05:36:09 2015 -0300

    [regression] Do not read from catchpoint/watchpoint locations' addresses when checking for a permanent breakpoint
    
    While running bare-metal tests with GDB i noticed some failures in
    gdb.base/break.exp, related to the use of the catch commands.
    
    It turns out GDB tries to access memory address 0x0 whenever one tries
    to insert a catchpoint, which should obviously not happen.
    
    This was introduced with the changes for permanent breakpoints. In special,
    bp_loc_is_permanent tries to check if there is a breakpoint inserted at
    the same address as the current breakpoint's location's address. In the
    case of catchpoints, this is 0x0.
    
    (top-gdb) catch fork
    Sending packet: $m0,1#fa...Packet received: E01
    Catchpoint 4 (fork)
    
    (top-gdb) catch vfork
    Sending packet: $m0,1#fa...Packet received: E01
    Catchpoint 5 (vfork)
    
    It is not obvious to detect because this fails silently for Linux. For our
    bare-metal testing, though, this fails with a clear error message from the
    target about not being able to read such address.
    
    The attached patch addresses this by bailing out of bp_loc_is_permanent (...)
    if the location address is not meaningful. I also took the opportunity to
    update the comment for breakpoint_address_is_meaningful, which mentioned
    breakpoint addresses as opposed to their locations' addresses.
    
    gdb/ChangeLog:
    
    2015-08-11  Luis Machado  <lgustavo@codesourcery.com>
    
    	* breakpoint.c (bp_loc_is_permanent): Return 0 when breakpoint
    	location address is not meaningful.
    	(breakpoint_address_is_meaningful): Update comment.

Diff:
---
 gdb/ChangeLog    |  6 ++++++
 gdb/breakpoint.c | 17 ++++++++++++-----
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 01e9938..4d60123 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2015-08-12  Luis Machado  <lgustavo@codesourcery.com>
+
+	* breakpoint.c (bp_loc_is_permanent): Return 0 when breakpoint
+	location address is not meaningful.
+	(breakpoint_address_is_meaningful): Update comment.
+
 2015-08-11  Keith Seitz  <keiths@redhat.com>
 
 	* NEWS: Mention explicit locations.
diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index bffff23..a6994c7 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -6963,14 +6963,14 @@ describe_other_breakpoints (struct gdbarch *gdbarch,
 
 
 /* Return true iff it is meaningful to use the address member of
-   BPT.  For some breakpoint types, the address member is irrelevant
-   and it makes no sense to attempt to compare it to other addresses
-   (or use it for any other purpose either).
+   BPT locations.  For some breakpoint types, the locations' address members
+   are irrelevant and it makes no sense to attempt to compare them to other
+   addresses (or use them for any other purpose either).
 
    More specifically, each of the following breakpoint types will
-   always have a zero valued address and we don't want to mark
+   always have a zero valued location address and we don't want to mark
    breakpoints of any of these types to be a duplicate of an actual
-   breakpoint at address zero:
+   breakpoint location at address zero:
 
       bp_watchpoint
       bp_catchpoint
@@ -9007,6 +9007,13 @@ bp_loc_is_permanent (struct bp_location *loc)
 
   gdb_assert (loc != NULL);
 
+  /* If we have a catchpoint or a watchpoint, just return 0.  We should not
+     attempt to read from the addresses the locations of these breakpoint types
+     point to.  program_breakpoint_here_p, below, will attempt to read
+     memory.  */
+  if (!breakpoint_address_is_meaningful (loc->owner))
+    return 0;
+
   cleanup = save_current_space_and_thread ();
   switch_to_program_space_and_thread (loc->pspace);