[PATCH v2 2/3] Avoid memcpys in regcache read_part/write_part for full registers.

Alan Hayward
2018-06-21T09:39:05Z

Additionally, tidy up the functions: Remove asserts, use gdb_byte,
update comments.

2018-06-21 Alan Hayward <alan.hayward@arm.com>

* regcache.c (readable_regcache::read_part): Avoid memcpy when
possible.
(regcache::write_part): Likewise.
(readable_regcache::cooked_read_part): Update comment.
(readable_regcache::cooked_write_part): Likewise.
* regcache.h: (readable_regcache::read_part): Likewise.
(regcache::write_part): Likewise.
---
gdb/regcache.c | 92 ++++++++++++++++++++++++++++++----------------------------
gdb/regcache.h | 12 +++++---
2 files changed, 55 insertions(+), 49 deletions(-)

diff --git a/gdb/regcache.c b/gdb/regcache.c
index 6276b149a2..fe4742c2ee 100644
--- a/gdb/regcache.c
+++ b/gdb/regcache.c
@@ -775,77 +775,75 @@ regcache::cooked_write (int regnum, const gdb_byte *buf)
regnum, buf);
}

-/* Perform a partial register transfer using a read, modify, write
- operation. */
+/* See regcache.h. */

enum register_status
-readable_regcache::read_part (int regnum, int offset, int len, void *in,
- bool is_raw)
+readable_regcache::read_part (int regnum, int offset, int len,
+ gdb_byte *out, bool is_raw)
{
- struct gdbarch *gdbarch = arch ();
- gdb_byte *reg = (gdb_byte *) alloca (register_size (gdbarch, regnum));
+ int reg_size = register_size (arch (), regnum);

- gdb_assert (in != NULL);
- gdb_assert (offset >= 0 && offset <= m_descr->sizeof_register[regnum]);
- gdb_assert (len >= 0 && offset + len <= m_descr->sizeof_register[regnum]);
- /* Something to do? */
- if (offset + len == 0)
+ gdb_assert (out != NULL);
+ gdb_assert (offset >= 0 && len >= 0 && offset + len <= reg_size);
+
+ if (offset == 0 && len == 0)
return REG_VALID;
- /* Read (when needed) ... */
+
+ if (offset == 0 && len == reg_size)
+ return (is_raw) ? raw_read (regnum, out) : cooked_read (regnum, out);
+
enum register_status status;
+ gdb_byte *reg = (gdb_byte *) alloca (reg_size);

- if (is_raw)
- status = raw_read (regnum, reg);
- else
- status = cooked_read (regnum, reg);
+ /* Read full register to buffer. */
+ status = (is_raw) ? raw_read (regnum, reg) : cooked_read (regnum, reg);
if (status != REG_VALID)
return status;

- /* ... modify ... */
- memcpy (in, reg + offset, len);
-
+ /* Copy out. */
+ memcpy (out, reg + offset, len);
return REG_VALID;
}

+/* See regcache.h. */
+
enum register_status
regcache::write_part (int regnum, int offset, int len,
- const void *out, bool is_raw)
+ const gdb_byte *in, bool is_raw)
{
- struct gdbarch *gdbarch = arch ();
- gdb_byte *reg = (gdb_byte *) alloca (register_size (gdbarch, regnum));
+ int reg_size = register_size (arch (), regnum);

- gdb_assert (out != NULL);
- gdb_assert (offset >= 0 && offset <= m_descr->sizeof_register[regnum]);
- gdb_assert (len >= 0 && offset + len <= m_descr->sizeof_register[regnum]);
- /* Something to do? */
- if (offset + len == 0)
+ gdb_assert (in != NULL);
+ gdb_assert (offset >= 0 && len >= 0 && offset + len <= reg_size);
+
+ if (offset == 0 && len == 0)
return REG_VALID;
- /* Read (when needed) ... */
- if (offset > 0
- || offset + len < m_descr->sizeof_register[regnum])
- {
- enum register_status status;

- if (is_raw)
- status = raw_read (regnum, reg);
- else
- status = cooked_read (regnum, reg);
- if (status != REG_VALID)
- return status;
+ if (offset == 0 && len == reg_size)
+ {
+ (is_raw) ? raw_write (regnum, in) : cooked_write (regnum, in);
+ return REG_VALID;
}

- memcpy (reg + offset, out, len);
- /* ... write (when needed). */
- if (is_raw)
- raw_write (regnum, reg);
- else
- cooked_write (regnum, reg);
+ enum register_status status;
+ gdb_byte *reg = (gdb_byte *) alloca (reg_size);
+
+ /* Read existing register to buffer. */
+ status = (is_raw) ? raw_read (regnum, reg) : cooked_read (regnum, reg);
+ if (status != REG_VALID)
+ return status;

+ /* Update buffer, then write back to regcache. */
+ memcpy (reg + offset, in, len);
+ is_raw ? raw_write (regnum, reg) : cooked_write (regnum, reg);
return REG_VALID;
}

+/* See regcache.h. */
+
enum register_status
-readable_regcache::raw_read_part (int regnum, int offset, int len, gdb_byte *buf)
+readable_regcache::raw_read_part (int regnum, int offset, int len,
+ gdb_byte *buf)
{
assert_regnum (regnum);
return read_part (regnum, offset, len, buf, true);
@@ -861,6 +859,8 @@ regcache::raw_write_part (int regnum, int offset, int len,
write_part (regnum, offset, len, buf, true);
}

+/* See regcache.h. */
+
enum register_status
readable_regcache::cooked_read_part (int regnum, int offset, int len,
gdb_byte *buf)
@@ -869,6 +869,8 @@ readable_regcache::cooked_read_part (int regnum, int offset, int len,
return read_part (regnum, offset, len, buf, false);
}

+/* See regcache.h. */
+
void
regcache::cooked_write_part (int regnum, int offset, int len,
const gdb_byte *buf)
diff --git a/gdb/regcache.h b/gdb/regcache.h
index 35c41888a7..c17ce09dee 100644
--- a/gdb/regcache.h
+++ b/gdb/regcache.h
@@ -253,8 +253,11 @@ public:
struct value *cooked_read_value (int regnum);

protected:
- enum register_status read_part (int regnum, int offset, int len, void *in,
- bool is_raw);
+
+ /* Perform a partial register transfer using a read, modify, write
+ operation. Will fail if register is currently invalid. */
+ enum register_status read_part (int regnum, int offset, int len,
+ gdb_byte *out, bool is_raw);
};

/* Buffer of registers, can be read and written. */
@@ -355,9 +358,10 @@ private:
int regnum, const void *in_buf,
void *out_buf, size_t size) const;

+ /* Perform a partial register transfer using a read, modify, write
+ operation. */
enum register_status write_part (int regnum, int offset, int len,
- const void *out, bool is_raw);
-
+ const gdb_byte *out, bool is_raw);

/* The address space of this register cache (for registers where it
makes sense, like PC or SP). */
--
2.15.2 (Apple Git-101.1)