21.4.4 MIPS

Alpha- and MIPS-based computers use an unusual stack frame, which sometimes requires GDB to search backward in the object code to find the beginning of a function.

To improve response time (especially for embedded applications, where GDB may be restricted to a slow serial line for this search) you may want to limit the size of this search, using one of these commands:

set heuristic-fence-post limit

Restrict GDB to examining at most limit bytes in its search for the beginning of a function. A value of 0 (the default) means there is no limit. However, except for 0, the larger the limit the more bytes heuristic-fence-post must search and therefore the longer it takes to run. You should only need to use this command when debugging a stripped executable.

show heuristic-fence-post

Display the current limit.

These commands are available only when GDB is configured for debugging programs on Alpha or MIPS processors.

Several MIPS-specific commands are available when debugging MIPS programs:

set mips abi arg

Tell GDB which MIPS ABI is used by the inferior. Possible values of arg are:

‘auto’

The default ABI associated with the current binary (this is the default).

‘o32’

‘o64’

‘n32’

‘n64’

‘eabi32’

‘eabi64’

show mips abi

Show the MIPS ABI used by GDB to debug the inferior.

set mips compression arg

Tell GDB which MIPS compressed ISA (Instruction Set Architecture) encoding is used by the inferior. GDB uses this for code disassembly and other internal interpretation purposes. This setting is only referred to when no executable has been associated with the debugging session or the executable does not provide information about the encoding it uses. Otherwise this setting is automatically updated from information provided by the executable.

Possible values of arg are ‘mips16’ and ‘micromips’. The default compressed ISA encoding is ‘mips16’, as executables containing MIPS16 code frequently are not identified as such.

This setting is “sticky”; that is, it retains its value across debugging sessions until reset either explicitly with this command or implicitly from an executable.

The compiler and/or assembler typically add symbol table annotations to identify functions compiled for the MIPS16 or microMIPS ISAs. If these function-scope annotations are present, GDB uses them in preference to the global compressed ISA encoding setting.

show mips compression

Show the MIPS compressed ISA encoding used by GDB to debug the inferior.

set mipsfpu

show mipsfpu

See set mipsfpu.

set mips mask-address arg

This command determines whether the most-significant 32 bits of 64-bit MIPS addresses are masked off. The argument arg can be ‘on’, ‘off’, or ‘auto’. The latter is the default setting, which lets GDB determine the correct value.

show mips mask-address

Show whether the upper 32 bits of MIPS addresses are masked off or not.

set remote-mips64-transfers-32bit-regs

This command controls compatibility with 64-bit MIPS targets that transfer data in 32-bit quantities. If you have an old MIPS 64 target that transfers 32 bits for some registers, like SR and FSR, and 64 bits for other registers, set this option to ‘on’.

show remote-mips64-transfers-32bit-regs

Show the current setting of compatibility with older MIPS 64 targets.

set debug mips

This command turns on and off debugging messages for the MIPS-specific target code in GDB.

show debug mips

Show the current setting of MIPS debugging messages.