command g

Format: ‘g’

Meaning: Read general registers.

Reply: ‘XX…’

Each byte of register data is described by two hex digits. The bytes with the register are transmitted in target byte order. The size of each register and their position within the ‘g’ packet are determined by the target description (see Target Descriptions); in the absence of a target description, this is done using code internal to GDB; typically this is some customary register layout for the architecture in question.

When reading registers, the stub may also return a string of literal ‘x’’s in place of the register data digits, to indicate that the corresponding register’s value is unavailable. For example, when reading registers from a trace frame (see Using the Collected Data), this means that the register has not been collected in the trace frame. When reading registers from a live program, this indicates that the stub has no means to access the register contents, even though the corresponding register is known to exist. Note that if a register truly does not exist on the target, then it is better to not include it in the target description in the first place.

Example: for an architecture with 4 registers of 4 bytes each, the following reply indicates to GDB that registers 0 and 2 are unavailable, while registers 1 and 3 are available, and both have zero value: gdb to gdb-server:

$g#00

gdb-server to gdb:

xxxxxxxx00000000xxxxxxxx00000000