CONFIG_MATH_EMULATION: Math emulation

General informations

The Linux kernel configuration item CONFIG_MATH_EMULATION has multiple definitions:

Math emulation found in arch/x86/Kconfig

The configuration item CONFIG_MATH_EMULATION:

• prompt: Math emulation
• type: bool
• depends on: ( CONFIG_MODIFY_LDT_SYSCALL ) && ( CONFIG_X86_32 && ( CONFIG_M486SX || CONFIG_MELAN ))
• defined in arch/x86/Kconfig
• found in Linux kernels: 2.6.24–2.6.39, 3.0–3.19, 4.0–4.20, 5.0–5.19, 6.0–6.8, 6.9-rc+HEAD

Help text

Linux can emulate a math coprocessor (used for floating point operations) if you don't have one. 486DX and Pentium processors have a math coprocessor built in, 486SX and 386 do not, unless you added a 487DX or 387, respectively. (The messages during boot time can give you some hints here ["man dmesg"].) Everyone needs either a coprocessor or this emulation.

If you don't have a math coprocessor, you need to say Y here; if you say Y here even though you have a coprocessor, the coprocessor will be used nevertheless. (This behavior can be changed with the kernel command line option "no387", which comes handy if your coprocessor is broken. Try "man bootparam" or see the documentation of your boot loader (lilo or loadlin) about how to pass options to the kernel at boot time.) This means that it is a good idea to say Y here if you intend to use this kernel on different machines.

More information about the internals of the Linux math coprocessor emulation can be found in arch/x86/math-emu/README.

If you are not sure, say Y; apart from resulting in a 66 KB bigger kernel, it won't hurt.

Math emulation found in arch/powerpc/Kconfig

The configuration item CONFIG_MATH_EMULATION:

• prompt: Math emulation
• type: bool
• depends on: CONFIG_4xx || CONFIG_PPC_8xx || CONFIG_PPC_MPC832x || CONFIG_BOOKE || CONFIG_PPC_MICROWATT
• defined in arch/powerpc/Kconfig
• found in Linux kernels: 2.6.15–2.6.39, 3.0–3.19, 4.0–4.20, 5.0–5.19, 6.0–6.8, 6.9-rc+HEAD

Help text

Some PowerPC chips designed for embedded applications do not have a floating-point unit and therefore do not implement the floating-point instructions in the PowerPC instruction set. If you say Y here, the kernel will include code to emulate a floating-point unit, which will allow programs that use floating-point instructions to run.

This is also useful to emulate missing (optional) instructions such as fsqrt on cores that do have an FPU but do not implement them (such as Freescale BookE).

Math emulation found in arch/xtensa/Kconfig

The configuration item CONFIG_MATH_EMULATION:

• prompt: Math emulation
• type: bool
• depends on: (none)
• defined in arch/xtensa/Kconfig
• found in Linux kernels: 2.6.13–2.6.39, 3.0–3.16

Help text

Can we use information of configuration file?

Math emulation found in arch/ppc/Kconfig

The configuration item CONFIG_MATH_EMULATION:

• prompt: Math emulation
• type: bool
• depends on: CONFIG_4xx || CONFIG_8xx
• defined in arch/ppc/Kconfig
• found in Linux kernels: 2.5.45–2.5.75, 2.6.0–2.6.26

Help text

Some PowerPC chips designed for embedded applications do not have a floating-point unit and therefore do not implement the floating-point instructions in the PowerPC instruction set. If you say Y here, the kernel will include code to emulate a floating-point unit, which will allow programs that use floating-point instructions to run.

If you have an Apple machine or an IBM RS/6000 or pSeries machine, or any machine with a 6xx, 7xx or 7xxx series processor, say N here. Saying Y here will not hurt performance (on any machine) but will increase the size of the kernel.

Math emulation found in arch/i386/Kconfig

The configuration item CONFIG_MATH_EMULATION:

• prompt: Math emulation
• type: bool
• depends on: (none)
• defined in arch/i386/Kconfig
• found in Linux kernels: 2.5.45–2.5.75, 2.6.0–2.6.23

Help text

Linux can emulate a math coprocessor (used for floating point operations) if you don't have one. 486DX and Pentium processors have a math coprocessor built in, 486SX and 386 do not, unless you added a 487DX or 387, respectively. (The messages during boot time can give you some hints here ["man dmesg"].) Everyone needs either a coprocessor or this emulation.

If you don't have a math coprocessor, you need to say Y here; if you say Y here even though you have a coprocessor, the coprocessor will be used nevertheless. (This behavior can be changed with the kernel command line option "no387", which comes handy if your coprocessor is broken. Try "man bootparam" or see the documentation of your boot loader (lilo or loadlin) about how to pass options to the kernel at boot time.) This means that it is a good idea to say Y here if you intend to use this kernel on different machines.

More information about the internals of the Linux math coprocessor emulation can be found in arch/i386/math-emu/README.

If you are not sure, say Y; apart from resulting in a 66 KB bigger kernel, it won't hurt.

found in arch/x86_64/Kconfig

The configuration item CONFIG_MATH_EMULATION:

• prompt:
• type: bool
• depends on: (none)
• defined in arch/x86_64/Kconfig
• found in Linux kernels: 2.5.45–2.5.75, 2.6.0–2.6.23

Help text

(none)

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The data is retrived from:

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