Re: [PATCH v2 04/10] Add regcache raw_compare method

Alan Hayward
2018-06-08T15:16:40Z

> On 7 Jun 2018, at 21:55, Simon Marchi <simon.marchi@ericsson.com> wrote:
>
> On 2018-06-06 11:16 AM, Alan Hayward wrote:
>> raw_compare returns the same as a memcmp (0 for success,
>> the diff otherwise). Kept with tristate return as this
>> feels potentally more useful than a simple true/false return.
>> (Happy to change if not).
>
> I would err on the bool side, but I don't really mind, the important is
> that it's documented properly. We still use many ints as bool in GDB, so
> someone seeing an int return value could easily think it's 0 -> not equal,
> 1 -> equal.

Ok, updated.

>
> Speaking of doc, I would suggest (as in the previous patch) to centralize
> the doc in the class/struct at the root, so we don't duplicate it.

Done.

>
>> 2018-06-06 Alan Hayward <alan.hayward@arm.com>
>>
>> gdb/
>> * common/common-regcache.h (raw_compare): New function.
>> * regcache.c (regcache::raw_compare): Likewise.
>> * regcache.h (regcache::raw_compare): New declaration.
>>
>> gdbserver/
>> * regcache.c (regcache::raw_compare): New function.
>> * regcache.h (regcache::raw_compare): New declaration.
>> ---
>> gdb/common/common-regcache.h | 1 +
>> gdb/gdbserver/regcache.c | 10 ++++++++++
>> gdb/gdbserver/regcache.h | 5 +++++
>> gdb/regcache.c | 15 +++++++++++++++
>> gdb/regcache.h | 11 +++++++++++
>> 5 files changed, 42 insertions(+)
>>
>> diff --git a/gdb/common/common-regcache.h b/gdb/common/common-regcache.h
>> index 487da0a7fb..e91439bec5 100644
>> --- a/gdb/common/common-regcache.h
>> +++ b/gdb/common/common-regcache.h
>> @@ -67,6 +67,7 @@ struct reg_buffer_common
>> virtual ~reg_buffer_common () = default;
>> virtual void raw_supply (int regnum, const void *buf) = 0;
>> virtual void raw_collect (int regnum, void *buf) const = 0;
>> + virtual int raw_compare (int regnum, const void *buf, int offset) const = 0;
>> virtual register_status get_register_status (int regnum) const = 0;
>> };
>>
>> diff --git a/gdb/gdbserver/regcache.c b/gdb/gdbserver/regcache.c
>> index 857721ee3d..9648428349 100644
>> --- a/gdb/gdbserver/regcache.c
>> +++ b/gdb/gdbserver/regcache.c
>> @@ -501,3 +501,13 @@ regcache::get_register_status (int regnum) const
>> return REG_VALID;
>> #endif
>> }
>> +
>> +/* See gdbserver/regcache.h. */
>> +
>> +int
>> +regcache::raw_compare (int regnum, const void *buf, int offset) const
>> +{
>> + gdb_assert (register_size (tdesc, regnum) > offset);
>
> Should we check ">= offset"? I think it could be useful for some edge cases
> where we could avoid an "if (offset < size)" in the caller, if we know offset
> could be equal to size. memcmp would return 0 (equal), which is fine.
>

Given that memcmp can cope with this, then ok.
(I need to make sure I update the patch that uses this function too!)

> Maybe assign "register_size (tdesc, regnum)" to a variable (e.g. reg_size)
> and use it in both places?

Done.

>
>> + return memcmp (buf, register_data (this, regnum, 1) + offset,
>> + register_size (tdesc, regnum) - offset);
>> +}
>> diff --git a/gdb/gdbserver/regcache.h b/gdb/gdbserver/regcache.h
>> index 1842f1d9cf..b26f39a8ad 100644
>> --- a/gdb/gdbserver/regcache.h
>> +++ b/gdb/gdbserver/regcache.h
>> @@ -50,6 +50,11 @@ struct regcache : public reg_buffer_common
>>
>> void raw_collect (int regnum, void *buf) const override;
>>
>> + /* Compare the contents of the register stored in the regcache (ignoring the
>> + first OFFSET bytes) to the contents of BUF (without any offset). Returns
>> + the same result as memcmp. */
>> + int raw_compare (int regnum, const void *buf, int offset) const override;
>> +
>> enum register_status get_register_status (int regnum) const override;
>> };
>>
>> diff --git a/gdb/regcache.c b/gdb/regcache.c
>> index a914b548ca..383e355e9f 100644
>> --- a/gdb/regcache.c
>> +++ b/gdb/regcache.c
>> @@ -1082,6 +1082,21 @@ regcache::collect_regset (const struct regset *regset,
>> transfer_regset (regset, NULL, regnum, NULL, buf, size);
>> }
>>
>> +/* See regcache.h. */
>> +
>> +int
>> +regcache::raw_compare (int regnum, const void *buf, int offset) const
>> +{
>> + const char *regbuf;
>> + size_t size;
>> +
>> + gdb_assert (buf != NULL);
>> + assert_regnum (regnum);
>
> Should we assert that offset is < or <= size here too?
>

Not sure why I didn’t add this.

Patch update with changes above. Are you ok with this version?

diff --git a/gdb/common/common-regcache.h b/gdb/common/common-regcache.h
index 29d9a81182ad1a5797b080e136b682fe59ecef37..fe3ece7ac52d60d07d718ad617f30be2f7133b5f 100644
--- a/gdb/common/common-regcache.h
+++ b/gdb/common/common-regcache.h
@@ -75,6 +75,11 @@ struct reg_buffer_common

/* Collect register REGNUM from REGCACHE and store its contents in BUF. */
virtual void raw_collect (int regnum, void *buf) const = 0;
+
+ /* Compare the contents of the register stored in the regcache (ignoring the
+ first OFFSET bytes) to the contents of BUF (without any offset). Returns
+ True if the same. */
+ virtual bool raw_compare (int regnum, const void *buf, int offset) const = 0;
};

#endif /* COMMON_REGCACHE_H */
diff --git a/gdb/gdbserver/regcache.h b/gdb/gdbserver/regcache.h
index 352c1df3f9eeacd622a3d5d668ff4ea98aea9c6f..b4c4c20ebd368f56f14af758301ff7d55fd16dae 100644
--- a/gdb/gdbserver/regcache.h
+++ b/gdb/gdbserver/regcache.h
@@ -54,6 +54,9 @@ struct regcache : public reg_buffer_common

/* See common/common-regcache.h. */
void raw_collect (int regnum, void *buf) const override;
+
+ /* See common/common-regcache.h. */
+ bool raw_compare (int regnum, const void *buf, int offset) const override;
};

struct regcache *init_register_cache (struct regcache *regcache,
diff --git a/gdb/gdbserver/regcache.c b/gdb/gdbserver/regcache.c
index 83837525a18c1dc96b6e9d24397064e247ced459..735ce7bccfc7a058f8604620928f3894d4655887 100644
--- a/gdb/gdbserver/regcache.c
+++ b/gdb/gdbserver/regcache.c
@@ -502,3 +502,17 @@ regcache::get_register_status (int regnum) const
return REG_VALID;
#endif
}
+
+/* See common/common-regcache.h. */
+
+bool
+regcache::raw_compare (int regnum, const void *buf, int offset) const
+{
+ gdb_assert (buf != NULL);
+
+ const unsigned char *regbuf = register_data (this, regnum, 1);
+ int size = register_size (tdesc, regnum);
+ gdb_assert (size >= offset);
+
+ return (memcmp (buf, regbuf + offset, size - offset) == 0);
+}
diff --git a/gdb/regcache.h b/gdb/regcache.h
index 4e5659b25bc530a4ced32520825136534be2e642..511864858d24a7fa53047fdc247846a551b121af 100644
--- a/gdb/regcache.h
+++ b/gdb/regcache.h
@@ -191,6 +191,10 @@ public:
xfree (m_registers);
xfree (m_register_status);
}
+
+ /* See common/common-regcache.h. */
+ bool raw_compare (int regnum, const void *buf, int offset) const override;
+
protected:
/* Assert on the range of REGNUM. */
void assert_regnum (int regnum) const;
diff --git a/gdb/regcache.c b/gdb/regcache.c
index 032fef0d34ac635c96dd6c39426f5c6d04f28095..fd0fd7318c8cca0083c897d2bd6ba1361dd627c0 100644
--- a/gdb/regcache.c
+++ b/gdb/regcache.c
@@ -1078,6 +1078,20 @@ regcache::collect_regset (const struct regset *regset,
transfer_regset (regset, NULL, regnum, NULL, buf, size);
}

+/* See common/common-regcache.h. */
+
+bool
+reg_buffer::raw_compare (int regnum, const void *buf, int offset) const
+{
+ gdb_assert (buf != NULL);
+ assert_regnum (regnum);
+
+ const char *regbuf = (const char *) register_buffer (regnum);
+ size_t size = m_descr->sizeof_register[regnum];
+ gdb_assert (size >= offset);
+
+ return (memcmp (buf, regbuf + offset, size - offset) == 0);
+}

/* Special handling for register PC. */