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authorJoel Brobecker <brobecker@gnat.com>2012-03-15 18:33:45 +0000
committerJoel Brobecker <brobecker@gnat.com>2012-03-15 18:33:45 +0000
commit35c63cd8ce5100859789b65ae76c6e5fe6ba47a4 (patch)
tree06b0067bd7fe07eb48b194b63dc353aab092ec9a
parent7b8957f8c3b4054061363abdc38bbbf0a3b20635 (diff)
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Problem after hitting breakpoint on Windows (with GDBserver)
When debugging on Windows with GDBserver, the debugger starts failing after hitting a breakpoint. For instance: (gdb) b foo Breakpoint 1 at 0x40177e: file foo.adb, line 5. (gdb) cont Continuing. Breakpoint 1, foo () at foo.adb:5 5 Put_Line ("Hello World."); -- STOP (gdb) n Program received signal SIGSEGV, Segmentation fault. 0x00401782 in foo () at foo.adb:5 5 Put_Line ("Hello World."); -- STOP There are two issues: 1. While trying to re-insert a breakpoint that is still inserted in memory, insert_bp_location wipes out the breakpoint location's shadow_contents. As a consequence, we cannot restore the proper instruction when removing the breakpoint anymore. That's why the inferior's behavior changes when trying to resume after the breakpoint was hit. 2. mem-break.c:default_memory_insert_breakpoint passes a breakpoint location's shadow_contents as the buffer for a memory read. This reveals a limitation of the various memory-read target functions. This patch documents this limitation and adjust the two calls that seem to hit that limitation. gdb/ChangeLog: * breakpoint.c (breakpoint_xfer_memory): Add assertion. Update function description. (insert_bp_location): Do not wipe bl->target_info out. * mem-break.c: #include "gdb_string.h". (default_memory_insert_breakpoint): Do not call target_read_memory with a pointer to the breakpoint's shadow_contents buffer. Use a local buffer instead. * m32r-tdep.c (m32r_memory_insert_breakpoint): Ditto.
-rw-r--r--gdb/ChangeLog11
-rw-r--r--gdb/breakpoint.c21
-rw-r--r--gdb/m32r-tdep.c3
-rw-r--r--gdb/mem-break.c17
4 files changed, 43 insertions, 9 deletions
diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 1a75508..875d675 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,14 @@
+2012-03-15 Joel Brobecker <brobecker@adacore.com>
+
+ * breakpoint.c (breakpoint_xfer_memory): Add assertion.
+ Update function description.
+ (insert_bp_location): Do not wipe bl->target_info out.
+ * mem-break.c: #include "gdb_string.h".
+ (default_memory_insert_breakpoint): Do not call target_read_memory
+ with a pointer to the breakpoint's shadow_contents buffer. Use
+ a local buffer instead.
+ * m32r-tdep.c (m32r_memory_insert_breakpoint): Ditto.
+
2012-03-15 Tom Tromey <tromey@redhat.com>
* NEWS: Mention "info vtbl", not "info vtable".
diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index d35704d..debf2b2 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -1318,6 +1318,10 @@ bp_location_has_shadow (struct bp_location *bl)
/* Update BUF, which is LEN bytes read from the target address MEMADDR,
by replacing any memory breakpoints with their shadowed contents.
+ If READBUF is not NULL, this buffer must not overlap with any of
+ the breakpoint location's shadow_contents buffers. Otherwise,
+ a failed assertion internal error will be raised.
+
The range of shadowed area by each bp_location is:
bl->address - bp_location_placed_address_before_address_max
up to bl->address + bp_location_shadow_len_after_address_max
@@ -1446,6 +1450,12 @@ breakpoint_xfer_memory (gdb_byte *readbuf, gdb_byte *writebuf,
if (readbuf != NULL)
{
+ /* Verify that the readbuf buffer does not overlap with
+ the shadow_contents buffer. */
+ gdb_assert (bl->target_info.shadow_contents >= readbuf + len
+ || readbuf >= (bl->target_info.shadow_contents
+ + bl->target_info.shadow_len));
+
/* Update the read buffer with this inserted breakpoint's
shadow. */
memcpy (readbuf + bp_addr - memaddr,
@@ -2082,8 +2092,15 @@ insert_bp_location (struct bp_location *bl,
if (!should_be_inserted (bl) || (bl->inserted && !bl->needs_update))
return 0;
- /* Initialize the target-specific information. */
- memset (&bl->target_info, 0, sizeof (bl->target_info));
+ /* Note we don't initialize bl->target_info, as that wipes out
+ the breakpoint location's shadow_contents if the breakpoint
+ is still inserted at that location. This in turn breaks
+ target_read_memory which depends on these buffers when
+ a memory read is requested at the breakpoint location:
+ Once the target_info has been wiped, we fail to see that
+ we have a breakpoint inserted at that address and thus
+ read the breakpoint instead of returning the data saved in
+ the breakpoint location's shadow contents. */
bl->target_info.placed_address = bl->address;
bl->target_info.placed_address_space = bl->pspace->aspace;
bl->target_info.length = bl->length;
diff --git a/gdb/m32r-tdep.c b/gdb/m32r-tdep.c
index 72872bd..d504eb3 100644
--- a/gdb/m32r-tdep.c
+++ b/gdb/m32r-tdep.c
@@ -85,7 +85,7 @@ m32r_memory_insert_breakpoint (struct gdbarch *gdbarch,
CORE_ADDR addr = bp_tgt->placed_address;
int val;
gdb_byte buf[4];
- gdb_byte *contents_cache = bp_tgt->shadow_contents;
+ gdb_byte contents_cache[4];
gdb_byte bp_entry[] = { 0x10, 0xf1 }; /* dpt */
/* Save the memory contents. */
@@ -93,6 +93,7 @@ m32r_memory_insert_breakpoint (struct gdbarch *gdbarch,
if (val != 0)
return val; /* return error */
+ memcpy (bp_tgt->shadow_contents, contents_cache, 4);
bp_tgt->placed_size = bp_tgt->shadow_len = 4;
/* Determine appropriate breakpoint contents and size for this address. */
diff --git a/gdb/mem-break.c b/gdb/mem-break.c
index 7d0e3f1..bd34fb2 100644
--- a/gdb/mem-break.c
+++ b/gdb/mem-break.c
@@ -29,6 +29,7 @@
#include "breakpoint.h"
#include "inferior.h"
#include "target.h"
+#include "gdb_string.h"
/* Insert a breakpoint on targets that don't have any better
@@ -46,6 +47,7 @@ default_memory_insert_breakpoint (struct gdbarch *gdbarch,
{
int val;
const unsigned char *bp;
+ gdb_byte *readbuf;
/* Determine appropriate breakpoint contents and size for this address. */
bp = gdbarch_breakpoint_from_pc
@@ -53,15 +55,18 @@ default_memory_insert_breakpoint (struct gdbarch *gdbarch,
if (bp == NULL)
error (_("Software breakpoints not implemented for this target."));
- /* Save the memory contents. */
+ /* Save the memory contents in the shadow_contents buffer and then
+ write the breakpoint instruction. */
bp_tgt->shadow_len = bp_tgt->placed_size;
- val = target_read_memory (bp_tgt->placed_address, bp_tgt->shadow_contents,
+ readbuf = alloca (bp_tgt->placed_size);
+ val = target_read_memory (bp_tgt->placed_address, readbuf,
bp_tgt->placed_size);
-
- /* Write the breakpoint. */
if (val == 0)
- val = target_write_raw_memory (bp_tgt->placed_address, bp,
- bp_tgt->placed_size);
+ {
+ memcpy (bp_tgt->shadow_contents, readbuf, bp_tgt->placed_size);
+ val = target_write_raw_memory (bp_tgt->placed_address, bp,
+ bp_tgt->placed_size);
+ }
return val;
}