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gdb: fix bugs in {get,put}_frame_register_bytes

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I found this only by inspection: the myaddr pointer in
{get,put}_frame_register_bytes is reset to `buffer.data ()` at each
iteration.  This means that we will always use the bytes at the
beginning of `buffer` to read or write to the registers, instead of
progressing in `buffer`.

Fix this by re-writing the functions to chip away the beginning of the
buffer array_view as we progress in reading or writing the data.

These bugs was introduced almost 3 years ago [1], and yet nobody
complained.  I'm wondering which architecture relies on that register
"overflow" behavior (reading or writing multiple consecutive registers
with one {get,put}_frame_register_bytes calls), and in which situation.
I find these functions a bit dangerous, if a caller mis-calculates
things, it could end up silently reading or writing to the next
register, even if it's not the intent.

If I could change it, I would prefer to have functions specifically made
for that ({get,put}_frame_register_bytes_consecutive or something like
that) and make {get,put}_frame_register_bytes only able to write within
a single register (which I presume represents most of the use cases of
the current {get,put}_frame_register_bytes).  If a caller mis-calculates
things and an overflow occurs while calling
{get,put}_frame_register_bytes, it would hit an assert.  The problem is
knowing which callers rely on the overflow behavior and which don't.

[1] bdec2917b1

Change-Id: I43bd4a9f7fa8419d388a2b20bdc57d652688ddf8
Reviewed-By: John Baldwin <jhb@FreeBSD.org>
Approved-By: Andrew Burgess <aburgess@redhat.com>
This commit is contained in:
Simon Marchi
2023-12-01 11:27:19 -05:00
parent 51e6b8cfd6
commit e94d1f726f
1 changed files with 23 additions and 40 deletions
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63
gdb/frame.c
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@@ -1483,9 +1483,6 @@ get_frame_register_bytes (frame_info_ptr frame, int regnum,
int *optimizedp, int *unavailablep)
{
struct gdbarch *gdbarch = get_frame_arch (frame);
int i;
int maxsize;
int numregs;
/* Skip registers wholly inside of OFFSET. */
while (offset >= register_size (gdbarch, regnum))
@@ -1496,9 +1493,9 @@ get_frame_register_bytes (frame_info_ptr frame, int regnum,
/* Ensure that we will not read beyond the end of the register file.
This can only ever happen if the debug information is bad. */
maxsize = -offset;
numregs = gdbarch_num_cooked_regs (gdbarch);
for (i = regnum; i < numregs; i++)
int maxsize = -offset;
int numregs = gdbarch_num_cooked_regs (gdbarch);
for (int i = regnum; i < numregs; i++)
{
int thissize = register_size (gdbarch, i);
@@ -1507,20 +1504,15 @@ get_frame_register_bytes (frame_info_ptr frame, int regnum,
maxsize += thissize;
}
int len = buffer.size ();
if (len > maxsize)
if (buffer.size () > maxsize)
error (_("Bad debug information detected: "
"Attempt to read %d bytes from registers."), len);
"Attempt to read %zu bytes from registers."), buffer.size ());
/* Copy the data. */
while (len > 0)
while (!buffer.empty ())
{
int curr_len = register_size (gdbarch, regnum) - offset;
if (curr_len > len)
curr_len = len;
gdb_byte *myaddr = buffer.data ();
int curr_len = std::min<int> (register_size (gdbarch, regnum) - offset,
buffer.size ());
if (curr_len == register_size (gdbarch, regnum))
{
@@ -1528,8 +1520,8 @@ get_frame_register_bytes (frame_info_ptr frame, int regnum,
CORE_ADDR addr;
int realnum;
frame_register (frame, regnum, optimizedp, unavailablep,
&lval, &addr, &realnum, myaddr);
frame_register (frame, regnum, optimizedp, unavailablep, &lval,
&addr, &realnum, buffer.data ());
if (*optimizedp || *unavailablep)
return false;
}
@@ -1548,13 +1540,12 @@ get_frame_register_bytes (frame_info_ptr frame, int regnum,
return false;
}
memcpy (myaddr, value->contents_all ().data () + offset,
curr_len);
copy (value->contents_all ().slice (offset, curr_len),
buffer.slice (0, curr_len));
release_value (value);
}
myaddr += curr_len;
len -= curr_len;
buffer = buffer.slice (curr_len);
offset = 0;
regnum++;
}
@@ -1579,36 +1570,28 @@ put_frame_register_bytes (frame_info_ptr frame, int regnum,
regnum++;
}
int len = buffer.size ();
/* Copy the data. */
while (len > 0)
while (!buffer.empty ())
{
int curr_len = register_size (gdbarch, regnum) - offset;
int curr_len = std::min<int> (register_size (gdbarch, regnum) - offset,
buffer.size ());
if (curr_len > len)
curr_len = len;
const gdb_byte *myaddr = buffer.data ();
if (curr_len == register_size (gdbarch, regnum))
{
put_frame_register (frame, regnum, myaddr);
}
put_frame_register (frame, regnum, buffer.data ());
else
{
struct value *value
value *value
= frame_unwind_register_value (frame_info_ptr (frame->next),
regnum);
gdb_assert (value != NULL);
gdb_assert (value != nullptr);
memcpy ((char *) value->contents_writeable ().data () + offset,
myaddr, curr_len);
put_frame_register (frame, regnum,
value->contents_raw ().data ());
copy (buffer.slice (0, curr_len),
value->contents_writeable ().slice (offset, curr_len));
put_frame_register (frame, regnum, value->contents_raw ().data ());
release_value (value);
}
myaddr += curr_len;
len -= curr_len;
buffer = buffer.slice (curr_len);
offset = 0;
regnum++;
}