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Support Segger J-Link #1206

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c42ea86
Always send checksum
hsorbo Nov 6, 2025
da446fc
Load props based on supported not attached
hsorbo Nov 6, 2025
8509d76
Allow qRcmd to return empty (unsupported)
hsorbo Nov 7, 2025
092758a
Detect vCont with fallback
hsorbo Jan 16, 2026
554b6c4
Support switching threads before reading registers
hsorbo Jan 16, 2026
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139 changes: 90 additions & 49 deletions src/gdb.vala
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Original file line number Diff line number Diff line change
Expand Up @@ -88,11 +88,6 @@ namespace Frida.GDB {
SKIP_ACKS
}

public enum ChecksumType {
PROPER,
ZEROED
}

protected const char NOTIFICATION_TYPE_EXIT_STATUS = 'W';
protected const char NOTIFICATION_TYPE_EXIT_SIGNAL = 'X';
protected const char NOTIFICATION_TYPE_STOP = 'S';
Expand Down Expand Up @@ -156,13 +151,16 @@ namespace Frida.GDB {
ack_mode = SKIP_ACKS;
}

if ("qXfer:features:read+" in supported_features) {
yield load_target_properties (cancellable);
}

yield detect_vendor_features (cancellable);

yield enable_extensions (cancellable);

string attached_response = yield query_property ("Attached", cancellable);
if (attached_response == "1") {
yield load_target_properties (cancellable);
if (_exception == null) {
request_stop_info ();
yield wait_until_stopped (cancellable);
Expand All @@ -187,6 +185,17 @@ namespace Frida.GDB {
throw (IOError) e;
}

try {
var response = yield query_simple ("vCont?", cancellable);
unowned string payload = response.payload;
if (payload.length > 0 && payload[0] != 'E' && payload != "") {
supported_features.add ("vcont");
}
} catch (GLib.Error e) {
if (e is IOError.CANCELLED)
throw (IOError) e;
}

try {
string response = yield query_property ("qemu.PhyMemMode", cancellable);
if (response.length == 1)
Expand Down Expand Up @@ -270,6 +279,8 @@ namespace Frida.GDB {

change_state (RUNNING);

//todo error if no vcont?

var command = make_packet_builder_sized (1)
.append ("vCont");
foreach (var thread in threads) {
Expand Down Expand Up @@ -398,12 +409,21 @@ namespace Frida.GDB {
check_stopped ();

change_state (RUNNING);
if ("vcont" in features) {
var command = make_packet_builder_sized (16)
.append ("vCont;s:")
.append (thread.id)
.build ();
write_bytes (command);
} else {
// Expensive roundtrip
yield execute_simple ("Hg" + thread.id, cancellable);
var command = make_packet_builder_sized (16)
.append ("s")
.build ();
write_bytes (command);
}

var command = make_packet_builder_sized (16)
.append ("vCont;s:")
.append (thread.id)
.build ();
write_bytes (command);

yield wait_until_stopped (cancellable);
}
Expand All @@ -413,12 +433,20 @@ namespace Frida.GDB {

change_state (RUNNING);

var command = make_packet_builder_sized (16)
.append ("vCont;s:")
.append (thread.id)
.append (";c")
.build ();
write_bytes (command);
if ("vcont" in features) {
var command = make_packet_builder_sized (16)
.append ("vCont;s:")
.append (thread.id)
.append (";c")
.build ();
write_bytes (command);
} else {
//todo: maybe throw, needs vCont
var command = make_packet_builder_sized (16)
.append ("s")
.build ();
write_bytes (command);
}
}

public virtual async Bytes read_byte_array (uint64 address, size_t size, Cancellable? cancellable = null)
Expand Down Expand Up @@ -552,7 +580,7 @@ namespace Frida.GDB {
var output = new Gee.ArrayList<Packet> ();
Packet response = yield query_with_predicate (builder.build (), packet => {
unowned string payload = packet.payload;
if (payload.has_prefix ("OK") || payload[0] == 'E')
if (payload.has_prefix ("OK") || payload[0] == 'E' || payload == "")
return COMPLETE;
if (payload[0] == NOTIFICATION_TYPE_OUTPUT) {
output.add (packet);
Expand Down Expand Up @@ -996,8 +1024,7 @@ namespace Frida.GDB {
}

public PacketBuilder make_packet_builder_sized (size_t capacity) {
var checksum_type = (ack_mode == SEND_ACKS) ? ChecksumType.PROPER : ChecksumType.ZEROED;
return new PacketBuilder (capacity, checksum_type);
return new PacketBuilder (capacity);
}

private async Packet read_packet () throws Error, IOError {
Expand Down Expand Up @@ -1118,11 +1145,9 @@ namespace Frida.GDB {
public sealed class PacketBuilder {
private StringBuilder? buffer;
private size_t initial_capacity;
private ChecksumType checksum_type;

public PacketBuilder (size_t capacity, ChecksumType checksum_type) {
public PacketBuilder (size_t capacity) {
this.initial_capacity = capacity + Packet.OVERHEAD;
this.checksum_type = checksum_type;

reset ();
}
Expand Down Expand Up @@ -1206,13 +1231,7 @@ namespace Frida.GDB {

public Bytes build () {
buffer.append_c (CHECKSUM_CHARACTER);

if (checksum_type == PROPER) {
buffer.append_printf ("%02x", compute_checksum (buffer.str, 1, buffer.len - 2));
} else {
buffer.append ("00");
}

buffer.append_printf ("%02x", compute_checksum (buffer.str, 1, buffer.len - 2));
return StringBuilder.free_to_bytes ((owned) buffer);
}
}
Expand Down Expand Up @@ -1676,34 +1695,56 @@ namespace Frida.GDB {

public async uint64 read_register (string name, Cancellable? cancellable = null) throws Error, IOError {
var reg = client.get_register_by_name (name);
Bytes request = null;
if ("vcont" in client.features) {
request = client.make_packet_builder_sized (32)
.append_c ('p')
.append_register_id (reg.id)
.append (";thread:")
.append (id)
.append_c (';')
.build ();
} else {
//todo: Expensive roundtrip, how can we avoid this?
yield client.execute_simple ("Hg" + id, cancellable);

var request = client.make_packet_builder_sized (32)
.append_c ('p')
.append_register_id (reg.id)
.append (";thread:")
.append (id)
.append_c (';')
.build ();

request = client.make_packet_builder_sized (32)
.append_c ('p')
.append_register_id (reg.id)
.build ();
}
var response = yield client.query (request, cancellable);

return Protocol.parse_integer_value (response.payload, client.byte_order);
}

public async void write_register (string name, uint64 val, Cancellable? cancellable = null) throws Error, IOError {
var reg = client.get_register_by_name (name);

var command = client.make_packet_builder_sized (48)
.append_c ('P')
.append_register_id (reg.id)
.append_c ('=')
.append (Protocol.unparse_integer_value (val, client.pointer_size, client.byte_order))
.append (";thread:")
.append (id)
.append_c (';')
.build ();
if ("vcont" in client.features) {
var command = client.make_packet_builder_sized (48)
.append_c ('P')
.append_register_id (reg.id)
.append_c ('=')
.append (Protocol.unparse_integer_value (val, client.pointer_size, client.byte_order))
.append (";thread:")
.append (id)
.append_c (';')
.build ();

yield client.execute (command, cancellable);
yield client.execute (command, cancellable);
} else {
//todo: Expensive roundtrip, how can we avoid this?
yield client.execute_simple ("Hg" + id, cancellable);

var command = client.make_packet_builder_sized (48)
.append_c ('P')
.append_register_id (reg.id)
.append_c ('=')
.append (Protocol.unparse_integer_value (val, client.pointer_size, client.byte_order))
.build ();

yield client.execute (command, cancellable);
}
}
}

Expand Down
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