[PATCH 19/43] Add new memory access interface to expr.c

Zoran Zaric via Gdb-patches
2021-03-01T14:47:18Z

DWARF expression evaluator is currently using a few different
interfaces for memory access: write_memory_with_notification,
read_value_memory, read_memory.

They all seem incosistent, while some of them even need a struct
value typed argument to be present.

This patch is simplifying that interface by replacing it with two new
low level functions: read_from_memory and write_to_memory.

The advantage of this new interface is that it behaves in the same way
as the register access interface from the previous patch. Both of these
have the same error returning policy, which will be usefull for the
following patches.

* dwarf2/expr.c (xfer_memory): New function.
(read_from_memory): New function.
(write_to_memory): New function.
(rw_pieced_value): Now calls the read_from_memory and
write_to_memory functions.
---
gdb/dwarf2/expr.c | 187 +++++++++++++++++++++++++++++++++++-----------
1 file changed, 144 insertions(+), 43 deletions(-)

diff --git a/gdb/dwarf2/expr.c b/gdb/dwarf2/expr.c
index 5a1fd5b941f..1abece7d173 100644
--- a/gdb/dwarf2/expr.c
+++ b/gdb/dwarf2/expr.c
@@ -32,6 +32,8 @@
#include "frame.h"
#include "gdbsupport/underlying.h"
#include "gdbarch.h"
+#include "inferior.h"
+#include "observable.h"

/* Cookie for gdbarch data. */

@@ -196,6 +198,85 @@ write_to_register (struct frame_info *frame, int regnum,
return;
}

+/* Helper for read_from_memory and write_to_memory. */
+
+static void
+xfer_memory (CORE_ADDR address, gdb_byte *readbuf,
+ const gdb_byte *writebuf,
+ size_t length, bool stack, int *unavailable)
+{
+ *unavailable = 0;
+
+ enum target_object object
+ = stack ? TARGET_OBJECT_STACK_MEMORY : TARGET_OBJECT_MEMORY;
+
+ ULONGEST xfered_total = 0;
+
+ while (xfered_total < length)
+ {
+ ULONGEST xfered_partial;
+
+ enum target_xfer_status status
+ = target_xfer_partial (current_top_target (), object, NULL,
+ (readbuf != nullptr
+ ? readbuf + xfered_total
+ : nullptr),
+ (writebuf != nullptr
+ ? writebuf + xfered_total
+ : nullptr),
+ address + xfered_total, length - xfered_total,
+ &xfered_partial);
+
+ if (status == TARGET_XFER_OK)
+ {
+ xfered_total += xfered_partial;
+ QUIT;
+ }
+ else if (status == TARGET_XFER_UNAVAILABLE)
+ {
+ *unavailable = 1;
+ return;
+ }
+ else if (status == TARGET_XFER_EOF)
+ memory_error (TARGET_XFER_E_IO, address + xfered_total);
+ else
+ memory_error (status, address + xfered_total);
+ }
+}
+
+/* Read LENGTH bytes of memory contents starting at ADDRESS.
+
+ The data read is copied to a caller-managed buffer BUF. STACK
+ indicates whether the memory range specified belongs to a stack
+ memory region.
+
+ If the memory is unavailable, the UNAVAILABLE output is set. */
+
+static void
+read_from_memory (CORE_ADDR address, gdb_byte *buffer,
+ size_t length, bool stack, int *unavailable)
+{
+ xfer_memory (address, buffer, nullptr, length, stack, unavailable);
+}
+
+/* Write LENGTH bytes of memory contents starting at ADDRESS.
+
+ The data written is copied from a caller-managed buffer buf. STACK
+ indicates whether the memory range specified belongs to a stack
+ memory region.
+
+ If the memory is unavailable, the UNAVAILABLE output is set. */
+
+static void
+write_to_memory (CORE_ADDR address, const gdb_byte *buffer,
+ size_t length, bool stack, int *unavailable)
+{
+ xfer_memory (address, nullptr, buffer, length, stack, unavailable);
+
+ gdb::observers::memory_changed.notify (current_inferior (), address,
+ length, buffer);
+}
+
struct piece_closure
{
/* Reference count. */
@@ -381,66 +462,86 @@ rw_pieced_value (struct value *v, struct value *from)
bits_to_skip += p->offset;

CORE_ADDR start_addr = p->v.mem.addr + bits_to_skip / 8;
+ bool in_stack_memory = p->v.mem.in_stack_memory;
+ int unavail = 0;

if (bits_to_skip % 8 == 0 && this_size_bits % 8 == 0
&& offset % 8 == 0)
{
/* Everything is byte-aligned; no buffer needed. */
if (from != NULL)
- write_memory_with_notification (start_addr,
- (from_contents
- + offset / 8),
- this_size_bits / 8);
+ write_to_memory (start_addr, (from_contents + offset / 8),
+ this_size_bits / 8, in_stack_memory,
+ &unavail);
else
- read_value_memory (v, offset,
- p->v.mem.in_stack_memory,
- p->v.mem.addr + bits_to_skip / 8,
- v_contents + offset / 8,
- this_size_bits / 8);
- break;
- }
-
- this_size = bits_to_bytes (bits_to_skip, this_size_bits);
- buffer.resize (this_size);
-
- if (from == NULL)
- {
- /* Read mode. */
- read_value_memory (v, offset,
- p->v.mem.in_stack_memory,
- p->v.mem.addr + bits_to_skip / 8,
- buffer.data (), this_size);
- copy_bitwise (v_contents, offset,
- buffer.data (), bits_to_skip % 8,
- this_size_bits, bits_big_endian);
+ read_from_memory (start_addr, (v_contents + offset / 8),
+ this_size_bits / 8, in_stack_memory,
+ &unavail);
}
else
{
- /* Write mode. */
- if (bits_to_skip % 8 != 0 || this_size_bits % 8 != 0)
+ this_size = bits_to_bytes (bits_to_skip, this_size_bits);
+ buffer.resize (this_size);
+
+ if (from == NULL)
{
- if (this_size <= 8)
+ /* Read mode. */
+ read_from_memory (start_addr, buffer.data (),
+ this_size, in_stack_memory,
+ &unavail);
+ if (!unavail)
+ copy_bitwise (v_contents, offset,
+ buffer.data (), bits_to_skip % 8,
+ this_size_bits, bits_big_endian);
+ }
+ else
+ {
+ /* Write mode. */
+ if (bits_to_skip % 8 != 0 || this_size_bits % 8 != 0)
{
- /* Perform a single read for small sizes. */
- read_memory (start_addr, buffer.data (),
- this_size);
+ if (this_size <= 8)
+ {
+ /* Perform a single read for small sizes. */
+ read_from_memory (start_addr, buffer.data (),
+ this_size, in_stack_memory,
+ &unavail);
+ }
+ else
+ {
+ /* Only the first and last bytes can possibly have
+ any bits reused. */
+ read_from_memory (start_addr, buffer.data (),
+ 1, in_stack_memory,
+ &unavail);
+ if (!unavail)
+ read_from_memory (start_addr + this_size - 1,
+ &buffer[this_size - 1], 1,
+ in_stack_memory, &unavail);
+ }
}
- else
+
+ if (!unavail)
{
- /* Only the first and last bytes can possibly have
- any bits reused. */
- read_memory (start_addr, buffer.data (), 1);
- read_memory (start_addr + this_size - 1,
- &buffer[this_size - 1], 1);
+ copy_bitwise (buffer.data (), bits_to_skip % 8,
+ from_contents, offset,
+ this_size_bits, bits_big_endian);
+ write_to_memory (start_addr, buffer.data (),
+ this_size, in_stack_memory,
+ &unavail);
}
}
+ }

- copy_bitwise (buffer.data (), bits_to_skip % 8,
- from_contents, offset,
- this_size_bits, bits_big_endian);
- write_memory_with_notification (start_addr,
- buffer.data (),
- this_size);
+ if (unavail)
+ {
+ if (from == NULL)
+ mark_value_bits_unavailable (v, (offset + bits_to_skip % 8),
+ this_size_bits);
+ else
+ throw_error (NOT_AVAILABLE_ERROR,
+ _("Can't do read-modify-write to "
+ "update bitfield; containing word "
+ "is unavailable"));
}
}
break;
--
2.17.1