gdb and binutils branch master updated. 0fec99e8be72b091618862eafc14e2741f0ff0d5

[palves at sourceware dot org]

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https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=0fec99e8be72b091618862eafc14e2741f0ff0d5

commit 0fec99e8be72b091618862eafc14e2741f0ff0d5
Author: Pedro Alves <palves@redhat.com>
Date:   Wed Oct 1 23:31:55 2014 +0100

    Really fail inserting software breakpoints on read-only regions
    
    Currently, with "set breakpoint auto-hw off", we'll still try to
    insert a software breakpoint at addresses covered by supposedly
    read-only or inacessible regions:
    
     (top-gdb) mem 0x443000 0x450000 ro
     (top-gdb) set mem inaccessible-by-default off
     (top-gdb) disassemble
     Dump of assembler code for function main:
        0x0000000000443956 <+34>:    movq   $0x0,0x10(%rax)
     => 0x000000000044395e <+42>:    movq   $0x0,0x18(%rax)
        0x0000000000443966 <+50>:    mov    -0x24(%rbp),%eax
        0x0000000000443969 <+53>:    mov    %eax,-0x20(%rbp)
     End of assembler dump.
     (top-gdb) b *0x0000000000443969
     Breakpoint 5 at 0x443969: file ../../src/gdb/gdb.c, line 29.
     (top-gdb) c
     Continuing.
     warning: cannot set software breakpoint at readonly address 0x443969
    
     Breakpoint 5, 0x0000000000443969 in main (argc=1, argv=0x7fffffffd918) at ../../src/gdb/gdb.c:29
     29        args.argc = argc;
     (top-gdb)
    
    We warn, saying that the insertion can't be done, but then proceed
    attempting the insertion anyway, and in case of manually added
    regions, the insert actually succeeds.
    
    This is a regression; GDB used to fail inserting the breakpoint.  More
    below.
    
    I stumbled on this as I wrote a test that manually sets up a read-only
    memory region with the "mem" command, in order to test GDB's behavior
    with breakpoints set on read-only regions, even when the real memory
    the breakpoints are set at isn't really read-only.  I wanted that in
    order to add a test that exercises software single-stepping through
    read-only regions.
    
    Note that the memory regions that target_memory_map returns aren't
    like e.g., what would expect to see in /proc/PID/maps on Linux.
    Instead, they're the physical memory map from the _debuggers_
    perspective.  E.g., a read-only region would be real ROM or flash
    memory, while a read-only+execute mapping in /proc/PID/maps is still
    read-write to the debugger (otherwise the debugger wouldn't be able to
    set software breakpoints in the code segment).
    
    If one tries to manually write to memory that falls within a memory
    region that is known to be read-only, with e.g., "p foo = 1", then we
    hit a check in memory_xfer_partial_1 before the write mananges to make
    it to the target side.
    
    But writing a software/memory breakpoint nowadays goes through
    target_write_raw_memory, and unlike when writing memory with
    TARGET_OBJECT_MEMORY, nothing on the TARGET_OBJECT_RAW_MEMORY path
    checks whether we're trying to write to a read-only region.
    
    At the time "breakpoint auto-hw" was added, we didn't have the
    TARGET_OBJECT_MEMORY vs TARGET_OBJECT_RAW_MEMORY target object
    distinction yet, and the code path in memory_xfer_partial that blocks
    writes to read-only memory was hit for memory breakpoints too.  With
    GDB 6.8 we had:
    
     warning: cannot set software breakpoint at readonly address 0000000000443943
     Warning:
     Cannot insert breakpoint 1.
     Error accessing memory address 0x443943: Input/output error.
    
    So I started out by fixing this by adding the memory region validation
    to TARGET_OBJECT_RAW_MEMORY too.
    
    But later, when testing against GDBserver, I realized that that would
    only block software/memory breakpoints GDB itself inserts with
    gdb/mem-break.c.  If a target has a to_insert_breakpoint method, the
    insertion request will still pass through to the target.  So I ended
    up converting the "cannot set breakpoint" warning in breakpoint.c to a
    real error return, thus blocking the insertion sooner.
    
    With that, we'll end up no longer needing the TARGET_OBJECT_RAW_MEMORY
    changes once software single-step breakpoints are converted to real
    breakpoints.  We need them today as software single-step breakpoints
    bypass insert_bp_location.  But, it'll be best to leave that in as
    safeguard anyway, for other direct uses of TARGET_OBJECT_RAW_MEMORY.
    
    Tested on x86_64 Fedora 20, native and gdbserver.
    
    gdb/
    2014-10-01  Pedro Alves  <palves@redhat.com>
    
    	* breakpoint.c (insert_bp_location): Error out if inserting a
    	software breakpoint at a read-only address.
    	* target.c (memory_xfer_check_region): New function, factored out
    	from ...
    	(memory_xfer_partial_1): ... this.  Make the 'reg_len' local a
    	ULONGEST.
    	(target_xfer_partial) <TARGET_OBJECT_RAW_MEMORY>: Check the access
    	against the memory region attributes.
    
    gdb/testsuite/
    2014-10-01  Pedro Alves  <palves@redhat.com>
    
    	* gdb.base/breakpoint-in-ro-region.c: New file.
    	* gdb.base/breakpoint-in-ro-region.exp: New file.

-----------------------------------------------------------------------

Summary of changes:
 gdb/ChangeLog                                      |   11 ++
 gdb/breakpoint.c                                   |   14 ++-
 gdb/target.c                                       |   95 +++++++++----
 gdb/testsuite/ChangeLog                            |    5 +
 gdb/testsuite/gdb.base/breakpoint-in-ro-region.c   |   28 ++++
 gdb/testsuite/gdb.base/breakpoint-in-ro-region.exp |  142 ++++++++++++++++++++
 6 files changed, 263 insertions(+), 32 deletions(-)
 create mode 100644 gdb/testsuite/gdb.base/breakpoint-in-ro-region.c
 create mode 100644 gdb/testsuite/gdb.base/breakpoint-in-ro-region.exp


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