What does GDB say when a register is not saved?
If some register is not saved, and GDB knows the register is “caller-saved” (via its own knowledge of the ABI, or because the debug/unwind info explicitly says the register’s value is undefined), GDB displays ‘ ’ as the register’s value.
When to use GDB to analyze memory and registers?
This is going to be a small demonstration or ‘tip’ to analyze registers and memory via gdb when debugging a program. These commands are pretty much useful when debugging a program. It has its own use cases.
Which is the command to see current registers in gdb?
$info registers is the command which can be used to see current register values at the moment from gdb prompt. Below command can be used as a short cut to view registers: Register information can be fetched individually .
Why is GDB not able to see volatile registers?
Usually ABIs reserve some registers as not needed to be saved by the callee (a.k.a.: “caller-saved”, “call-clobbered” or “volatile” registers). It may therefore not be possible for GDB to know the value a register had before the call (in other words, in the outer frame), if the register value has since been changed by the callee.
How to print register values in gdb command line?
Then you can get the register name you are interested in — very useful for finding platform-specific registers (like NEON Q… on ARM). If only want check it once, info registers show registers. If only want watch one register, for example, display $esp continue display esp registers in gdb command line.
Which is an alias for the EFLAGS register in gdb?
For example, on the SPARC, info registers displays the processor status register as $psr but you can also refer to it as $ps; and on x86-based machines $ps is an alias for the EFLAGS register. GDB always considers the contents of an ordinary register as an integer when the register is examined in this way.