[v6,6/8] gdb: Add qIsAddressTagged packet
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Commit Message
This commit adds a new packet, qIsAddressTagged, allowing GDB remote
targets to use it to query the stub if a given address is tagged.
Currently, the memory tagging address check is done via a read query,
where the contents of /proc/<PID>/smaps is read and the flags are
inspected for memory tagging-related flags that indicate the address is
in a memory tagged region.
This is not ideal, for example, for QEMU stub and other cases, such as
on bare-metal, where there is no notion of an OS file like 'smaps.'
Hence, the introduction of qIsAddressTagged packet allows checking
if an address is tagged in an agnostic way.
The is_address_tagged target hook in remote.c attempts to use the
qIsAddressTagged packet first for checking if an address is tagged and
if the stub does not support such a packet (reply is empty) it falls
back to using the current mechanism that reads the contents of
/proc/<PID>/smaps via vFile requests.
Signed-off-by: Gustavo Romero <gustavo.romero@linaro.org>
---
gdb/remote.c | 75 ++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 75 insertions(+)
Comments
On 4/18/24 21:10, Gustavo Romero wrote:
> This commit adds a new packet, qIsAddressTagged, allowing GDB remote
> targets to use it to query the stub if a given address is tagged.
>
> Currently, the memory tagging address check is done via a read query,
> where the contents of /proc/<PID>/smaps is read and the flags are
> inspected for memory tagging-related flags that indicate the address is
> in a memory tagged region.
>
> This is not ideal, for example, for QEMU stub and other cases, such as
> on bare-metal, where there is no notion of an OS file like 'smaps.'
> Hence, the introduction of qIsAddressTagged packet allows checking
> if an address is tagged in an agnostic way.
>
> The is_address_tagged target hook in remote.c attempts to use the
> qIsAddressTagged packet first for checking if an address is tagged and
> if the stub does not support such a packet (reply is empty) it falls
> back to using the current mechanism that reads the contents of
> /proc/<PID>/smaps via vFile requests.
>
> Signed-off-by: Gustavo Romero <gustavo.romero@linaro.org>
> ---
> gdb/remote.c | 75 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 75 insertions(+)
>
> diff --git a/gdb/remote.c b/gdb/remote.c
> index cd271c4b493..3d034bb1ef8 100644
> --- a/gdb/remote.c
> +++ b/gdb/remote.c
> @@ -337,6 +337,9 @@ enum {
> packets and the tag violation stop replies. */
> PACKET_memory_tagging_feature,
>
> + /* Support for the qIsAddressTagged packet. */
> + PACKET_qIsAddressTagged,
> +
> PACKET_MAX
> };
>
> @@ -15535,6 +15538,50 @@ create_store_memtags_request (gdb::char_vector &packet, CORE_ADDR address,
> strcpy (packet.data (), request.c_str ());
> }
>
> +static void
> +create_is_address_tagged_request (gdbarch *gdbarch, gdb::char_vector &packet,
> + CORE_ADDR address)
> +{
> + int addr_size;
> + std::string request;
> +
> + addr_size = gdbarch_addr_bit (gdbarch) / 8;
> + request = string_printf ("qIsAddressTagged:%s", phex_nz (address, addr_size));
> +
> + if (packet.size () < request.length () + 1)
> + error (_("Contents too big for packet qIsAddressTagged."));
> +
> + strcpy (packet.data (), request.c_str ());
> +}
> +
> +static bool
> +check_is_address_tagged_reply (remote_target *remote, gdb::char_vector &packet,
> + bool &tagged)
> +{
> + gdb_assert (remote != nullptr);
> + /* Check reply and disable qIsAddressTagged usage if it's not supported. */
> + packet_result result = remote->m_features.packet_ok (packet,
> + PACKET_qIsAddressTagged);
> +
> + /* Return false on error (Exx), empty reply (packet not supported), or reply
> + size doesn't match 2 hex digits. */
> + if ((result.status () != PACKET_OK) || (strlen (packet.data ()) != 2))
> + return false;
> +
> + gdb_byte reply;
> + /* Convert only 2 hex digits, i.e. 1 byte in hex format. */
> + hex2bin (packet.data (), &reply, 1);
> +
> + if (reply == 0x00 || reply == 0x01)
> + {
> + tagged = !!reply;
> + return true;
> + }
> +
> + /* Invalid reply. */
> + return false;
> +}
> +
> /* Implement the "fetch_memtags" target_ops method. */
>
> bool
> @@ -15581,6 +15628,31 @@ remote_target::store_memtags (CORE_ADDR address, size_t len,
> bool
> remote_target::is_address_tagged (gdbarch *gdbarch, CORE_ADDR address)
> {
> + /* Firstly, attempt to check the address using the qIsAddressTagged
> + packet. */
> + if (m_features.packet_support (PACKET_qIsAddressTagged) != PACKET_DISABLE)
> + {
> + remote_target *remote = get_current_remote_target ();
> + struct remote_state *rs = get_remote_state ();
> + bool is_addr_tagged;
> +
> + create_is_address_tagged_request (gdbarch, rs->buf, address);
> +
> + putpkt (rs->buf);
> + getpkt (&rs->buf);
> +
> + /* If qIsAddressTagged is not supported PACKET_qIsAddressTagged will be
> + set to PACKET_DISABLE so no further attempt is made to check addresses
> + using this packet and the fallback mechanism below will be used
> + instead. Also, if the check fails due to an error (Exx reply) the
> + fallback is used too. Otherwise, the qIsAddressTagged query succeeded
> + and is_addr_tagged is valid. */
> + if (check_is_address_tagged_reply (remote, rs->buf, is_addr_tagged))
> + return is_addr_tagged;
> + }
> +
> + /* Fallback to arch-specific method of checking whether an address is tagged
> + in case check via qIsAddressTagged fails. */
> return gdbarch_tagged_address_p (gdbarch, address);
> }
>
> @@ -16070,6 +16142,9 @@ Show the maximum size of the address (in bits) in a memory packet."), NULL,
> add_packet_config_cmd (PACKET_memory_tagging_feature,
> "memory-tagging-feature", "memory-tagging-feature", 0);
>
> + add_packet_config_cmd (PACKET_qIsAddressTagged,
> + "qIsAddressTagged", "memory-tagging-address-check", 0);
> +
> /* Assert that we've registered "set remote foo-packet" commands
> for all packet configs. */
> {
Thanks, this is OK.
Approved-By: Luis Machado <luis.machado@arm.com>
Tested-By: Luis Machado <luis.machado@arm.com>
@@ -337,6 +337,9 @@ enum {
packets and the tag violation stop replies. */
PACKET_memory_tagging_feature,
+ /* Support for the qIsAddressTagged packet. */
+ PACKET_qIsAddressTagged,
+
PACKET_MAX
};
@@ -15535,6 +15538,50 @@ create_store_memtags_request (gdb::char_vector &packet, CORE_ADDR address,
strcpy (packet.data (), request.c_str ());
}
+static void
+create_is_address_tagged_request (gdbarch *gdbarch, gdb::char_vector &packet,
+ CORE_ADDR address)
+{
+ int addr_size;
+ std::string request;
+
+ addr_size = gdbarch_addr_bit (gdbarch) / 8;
+ request = string_printf ("qIsAddressTagged:%s", phex_nz (address, addr_size));
+
+ if (packet.size () < request.length () + 1)
+ error (_("Contents too big for packet qIsAddressTagged."));
+
+ strcpy (packet.data (), request.c_str ());
+}
+
+static bool
+check_is_address_tagged_reply (remote_target *remote, gdb::char_vector &packet,
+ bool &tagged)
+{
+ gdb_assert (remote != nullptr);
+ /* Check reply and disable qIsAddressTagged usage if it's not supported. */
+ packet_result result = remote->m_features.packet_ok (packet,
+ PACKET_qIsAddressTagged);
+
+ /* Return false on error (Exx), empty reply (packet not supported), or reply
+ size doesn't match 2 hex digits. */
+ if ((result.status () != PACKET_OK) || (strlen (packet.data ()) != 2))
+ return false;
+
+ gdb_byte reply;
+ /* Convert only 2 hex digits, i.e. 1 byte in hex format. */
+ hex2bin (packet.data (), &reply, 1);
+
+ if (reply == 0x00 || reply == 0x01)
+ {
+ tagged = !!reply;
+ return true;
+ }
+
+ /* Invalid reply. */
+ return false;
+}
+
/* Implement the "fetch_memtags" target_ops method. */
bool
@@ -15581,6 +15628,31 @@ remote_target::store_memtags (CORE_ADDR address, size_t len,
bool
remote_target::is_address_tagged (gdbarch *gdbarch, CORE_ADDR address)
{
+ /* Firstly, attempt to check the address using the qIsAddressTagged
+ packet. */
+ if (m_features.packet_support (PACKET_qIsAddressTagged) != PACKET_DISABLE)
+ {
+ remote_target *remote = get_current_remote_target ();
+ struct remote_state *rs = get_remote_state ();
+ bool is_addr_tagged;
+
+ create_is_address_tagged_request (gdbarch, rs->buf, address);
+
+ putpkt (rs->buf);
+ getpkt (&rs->buf);
+
+ /* If qIsAddressTagged is not supported PACKET_qIsAddressTagged will be
+ set to PACKET_DISABLE so no further attempt is made to check addresses
+ using this packet and the fallback mechanism below will be used
+ instead. Also, if the check fails due to an error (Exx reply) the
+ fallback is used too. Otherwise, the qIsAddressTagged query succeeded
+ and is_addr_tagged is valid. */
+ if (check_is_address_tagged_reply (remote, rs->buf, is_addr_tagged))
+ return is_addr_tagged;
+ }
+
+ /* Fallback to arch-specific method of checking whether an address is tagged
+ in case check via qIsAddressTagged fails. */
return gdbarch_tagged_address_p (gdbarch, address);
}
@@ -16070,6 +16142,9 @@ Show the maximum size of the address (in bits) in a memory packet."), NULL,
add_packet_config_cmd (PACKET_memory_tagging_feature,
"memory-tagging-feature", "memory-tagging-feature", 0);
+ add_packet_config_cmd (PACKET_qIsAddressTagged,
+ "qIsAddressTagged", "memory-tagging-address-check", 0);
+
/* Assert that we've registered "set remote foo-packet" commands
for all packet configs. */
{