How to print register values in GDB?

Question

info registers shows all the registers; info registers eax shows just the register eax. The command can be abbreviated as i r

If you're trying to print a specific register in GDB, you have to omit the % sign. For example,

info registers eip

If your executable is 64 bit, the registers start with r. Starting them with e is not valid.

info registers rip

Those can be abbreviated to:

i r rip

There is also:

info all-registers

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.
• If want watch all registers, layout regs continue show registers, with TUI mode.

Gdb commands:

• i r <register_name>: print a single register, e.g i r rax, i r eax
• i r <register_name_1> <register_name_2> ...: print multiple registers, e.g i r rdi rsi,
• i r: print all register except floating point & vector register (xmm, ymm, zmm).
• i r a: print all register, include floating point & vector register (xmm, ymm, zmm).
• i r f: print all FPU floating registers (st0-7 and a few other f*)

Other register groups besides a (all) and f (float) can be found with:

maint print reggroups

as documented at: https://sourceware.org/gdb/current/onlinedocs/gdb/Registers.html#Registers

Tips:

• xmm0 ~ xmm15, are 128 bits, almost every modern machine has it, they are released in 1999.
• ymm0 ~ ymm15, are 256 bits, new machine usually have it, they are released in 2011.
• zmm0 ~ zmm31, are 512 bits, normal pc probably don't have it (as the year 2016), they are released in 2013, and mainly used in servers so far.
• Only one serial of xmm / ymm / zmm will be shown, because they are the same registers in different mode. On my machine ymm is shown.