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https://github.com/darlinghq/darling-gdb.git
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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.
This commit is contained in:
Pedro Alves
parent
2ddf430110
commit
0fec99e8be
@ -1,3 +1,14 @@
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2014-10-01 Pedro Alves <palves@redhat.com>
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* breakpoint.c (insert_bp_location): Error out if inserting a
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software breakpoint at a read-only address.
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* target.c (memory_xfer_check_region): New function, factored out
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from ...
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(memory_xfer_partial_1): ... this. Make the 'reg_len' local a
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ULONGEST.
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(target_xfer_partial) <TARGET_OBJECT_RAW_MEMORY>: Check the access
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against the memory region attributes.
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2014-10-01 Simon Marchi <simon.marchi@ericsson.com>
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* NEWS: Announce new exit-code field in -list-thread-groups
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@ -2674,10 +2674,16 @@ insert_bp_location (struct bp_location *bl,
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}
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}
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else if (bl->loc_type == bp_loc_software_breakpoint
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&& mr->attrib.mode != MEM_RW)
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warning (_("cannot set software breakpoint "
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"at readonly address %s"),
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paddress (bl->gdbarch, bl->address));
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&& mr->attrib.mode != MEM_RW)
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{
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fprintf_unfiltered (tmp_error_stream,
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_("Cannot insert breakpoint %d.\n"
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"Cannot set software breakpoint "
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"at read-only address %s\n"),
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bl->owner->number,
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paddress (bl->gdbarch, bl->address));
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return 1;
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}
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}
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}
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95
gdb/target.c
95
gdb/target.c
@ -909,6 +909,59 @@ target_section_by_addr (struct target_ops *target, CORE_ADDR addr)
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return NULL;
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}
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/* Helper for the memory xfer routines. Checks the attributes of the
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memory region of MEMADDR against the read or write being attempted.
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If the access is permitted returns true, otherwise returns false.
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REGION_P is an optional output parameter. If not-NULL, it is
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filled with a pointer to the memory region of MEMADDR. REG_LEN
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returns LEN trimmed to the end of the region. This is how much the
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caller can continue requesting, if the access is permitted. A
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single xfer request must not straddle memory region boundaries. */
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static int
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memory_xfer_check_region (gdb_byte *readbuf, const gdb_byte *writebuf,
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ULONGEST memaddr, ULONGEST len, ULONGEST *reg_len,
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struct mem_region **region_p)
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{
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struct mem_region *region;
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region = lookup_mem_region (memaddr);
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if (region_p != NULL)
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*region_p = region;
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switch (region->attrib.mode)
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{
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case MEM_RO:
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if (writebuf != NULL)
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return 0;
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break;
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case MEM_WO:
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if (readbuf != NULL)
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return 0;
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break;
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case MEM_FLASH:
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/* We only support writing to flash during "load" for now. */
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if (writebuf != NULL)
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error (_("Writing to flash memory forbidden in this context"));
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break;
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case MEM_NONE:
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return 0;
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}
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/* region->hi == 0 means there's no upper bound. */
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if (memaddr + len < region->hi || region->hi == 0)
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*reg_len = len;
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else
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*reg_len = region->hi - memaddr;
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return 1;
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}
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/* Read memory from more than one valid target. A core file, for
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instance, could have some of memory but delegate other bits to
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the target below it. So, we must manually try all targets. */
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@ -970,7 +1023,7 @@ memory_xfer_partial_1 (struct target_ops *ops, enum target_object object,
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ULONGEST len, ULONGEST *xfered_len)
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{
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enum target_xfer_status res;
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int reg_len;
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ULONGEST reg_len;
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struct mem_region *region;
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struct inferior *inf;
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@ -1017,34 +1070,10 @@ memory_xfer_partial_1 (struct target_ops *ops, enum target_object object,
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}
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/* Try GDB's internal data cache. */
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region = lookup_mem_region (memaddr);
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/* region->hi == 0 means there's no upper bound. */
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if (memaddr + len < region->hi || region->hi == 0)
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reg_len = len;
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else
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reg_len = region->hi - memaddr;
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switch (region->attrib.mode)
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{
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case MEM_RO:
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if (writebuf != NULL)
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return TARGET_XFER_E_IO;
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break;
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case MEM_WO:
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if (readbuf != NULL)
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return TARGET_XFER_E_IO;
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break;
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case MEM_FLASH:
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/* We only support writing to flash during "load" for now. */
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if (writebuf != NULL)
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error (_("Writing to flash memory forbidden in this context"));
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break;
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case MEM_NONE:
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return TARGET_XFER_E_IO;
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}
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if (!memory_xfer_check_region (readbuf, writebuf, memaddr, len, ®_len,
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®ion))
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return TARGET_XFER_E_IO;
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if (!ptid_equal (inferior_ptid, null_ptid))
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inf = find_inferior_pid (ptid_get_pid (inferior_ptid));
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@ -1184,6 +1213,16 @@ target_xfer_partial (struct target_ops *ops,
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writebuf, offset, len, xfered_len);
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else if (object == TARGET_OBJECT_RAW_MEMORY)
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{
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/* Skip/avoid accessing the target if the memory region
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attributes block the access. Check this here instead of in
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raw_memory_xfer_partial as otherwise we'd end up checking
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this twice in the case of the memory_xfer_partial path is
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taken; once before checking the dcache, and another in the
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tail call to raw_memory_xfer_partial. */
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if (!memory_xfer_check_region (readbuf, writebuf, offset, len, &len,
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NULL))
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return TARGET_XFER_E_IO;
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/* Request the normal memory object from other layers. */
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retval = raw_memory_xfer_partial (ops, readbuf, writebuf, offset, len,
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xfered_len);
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@ -1,3 +1,8 @@
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2014-10-01 Pedro Alves <palves@redhat.com>
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* gdb.base/breakpoint-in-ro-region.c: New file.
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* gdb.base/breakpoint-in-ro-region.exp: New file.
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2014-10-01 Simon Marchi <simon.marchi@ericsson.com>
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* gdb.mi/mi-exit-code.exp: New file.
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28
gdb/testsuite/gdb.base/breakpoint-in-ro-region.c
Normal file
28
gdb/testsuite/gdb.base/breakpoint-in-ro-region.c
Normal file
@ -0,0 +1,28 @@
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/* This testcase is part of GDB, the GNU debugger.
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Copyright 2014 Free Software Foundation, Inc.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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volatile int i;
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int
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main (void)
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{
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i = 0;
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i = 0;
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i = 0;
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return 0;
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}
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142
gdb/testsuite/gdb.base/breakpoint-in-ro-region.exp
Normal file
142
gdb/testsuite/gdb.base/breakpoint-in-ro-region.exp
Normal file
@ -0,0 +1,142 @@
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# Copyright 2014 Free Software Foundation, Inc.
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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# This file is part of the gdb testsuite
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standard_testfile
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if { [prepare_for_testing "failed to prepare" $testfile $srcfile] } {
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return -1
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}
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if ![runto main] {
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return -1
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}
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delete_breakpoints
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# Get the bounds of a function, and write them to FUNC_LO (inclusive),
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# FUNC_HI (exclusive). Return true on success and false on failure.
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proc get_function_bounds {function func_lo func_hi} {
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global gdb_prompt
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global hex decimal
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upvar $func_lo lo
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upvar $func_hi hi
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set lo ""
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set size ""
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set test "get lo address of $function"
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gdb_test_multiple "disassemble $function" $test {
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-re "($hex) .*$hex <\\+($decimal)>:\[^\r\n\]+\r\nEnd of assembler dump\.\r\n$gdb_prompt $" {
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set lo $expect_out(1,string)
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set size $expect_out(2,string)
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pass $test
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}
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}
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if { $lo == "" || $size == "" } {
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return false
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}
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# Account for the size of the last instruction.
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set test "get hi address of $function"
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gdb_test_multiple "x/2i $function+$size" $test {
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-re ".*$hex <$function\\+$size>:\[^\r\n\]+\r\n\[ \]+($hex).*\.\r\n$gdb_prompt $" {
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set hi $expect_out(1,string)
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pass $test
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}
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}
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if { $hi == "" } {
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return false
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}
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# Remove unnecessary leading 0's (0x00000ADDR => 0xADDR) so we can
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# easily do matches. Disassemble includes leading zeros, while
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# x/i doesn't.
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regsub -all "0x0\+" $lo "0x" lo
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regsub -all "0x0\+" $hi "0x" hi
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return true
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}
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# Get the address where the thread is currently stopped.
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proc get_curr_insn {} {
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global gdb_prompt
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global hex
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set pc ""
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set test "get current insn"
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gdb_test_multiple "p /x \$pc" $test {
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-re " = ($hex)\r\n$gdb_prompt $" {
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set pc $expect_out(1,string)
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pass $test
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}
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}
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return $pc
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}
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# Get the address of where a single-step should land.
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proc get_next_insn {} {
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global gdb_prompt
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global hex
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set next ""
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set test "get next insn"
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gdb_test_multiple "x/2i \$pc" $test {
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-re "$hex .*:\[^\r\n\]+\r\n\[ \]+($hex).*\.\r\n$gdb_prompt $" {
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set next $expect_out(1,string)
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pass $test
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}
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}
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return $next
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}
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if ![get_function_bounds "main" main_lo main_hi] {
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# Can't do the following tests if main's bounds are unknown.
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return -1
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}
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# Manually create a read-only memory region that covers 'main'.
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gdb_test_no_output "mem $main_lo $main_hi ro" \
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"create read-only mem region covering main"
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# So that we don't fail inserting breakpoints on addresses outside
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# main, like the internal event breakpoints.
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gdb_test_no_output "set mem inaccessible-by-default off"
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# So we get an immediate warning/error without needing to resume the
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# target.
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gdb_test_no_output "set breakpoint always-inserted on"
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# Disable the automatic fallback to HW breakpoints. We want a
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# software breakpoint to be attempted, and to fail.
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gdb_test_no_output "set breakpoint auto-hw off"
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# Confirm manual writes to the read-only memory region fail.
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gdb_test "p /x *(char *) $main_lo = 1" \
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"Cannot access memory at address $main_lo" \
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"writing to read-only memory fails"
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# Ensure that inserting a software breakpoint in a known-read-only
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# region fails.
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gdb_test "break *$main_lo" \
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"Cannot insert breakpoint .*Cannot set software breakpoint at read-only address $main_lo.*" \
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"inserting software breakpoint in read-only memory fails"
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