Commit 0005e55a authored by Russell King's avatar Russell King
Browse files

ARM: net: bpf: correct stack layout documentation 



The stack layout documentation incorrectly suggests that the BPF JIT
scratch space starts immediately below BPF_FP. This is not correct,
so let's fix the documentation to reflect reality.

Signed-off-by: default avatarRussell King <rmk+kernel@armlinux.org.uk>
parent 70ec3a6c

arch/arm/net/bpf_jit_32.c

+27 −8
Original line number Diff line number Diff line
@@ -28,24 +28,43 @@ 
int bpf_jit_enable __read_mostly;



/*

 * eBPF prog stack layout

 * eBPF prog stack layout:

 *

 *                         high

 * original ARM_SP =>     +-----+ eBPF prologue

 *                        |FP/LR|

 * current ARM_FP =>      +-----+

 *                        | ... | callee saved registers

 * eBPF fp register =>    +-----+ <= (BPF_FP)

 * original ARM_SP =>     +-----+

 *                        |     | callee saved registers

 *                        +-----+ <= (BPF_FP + SCRATCH_SIZE)

 *                        | ... | eBPF JIT scratch space

 *                        |     | eBPF prog stack

 * eBPF fp register =>    +-----+

 *   (BPF_FP)             | ... | eBPF prog stack

 *                        +-----+

 *                        |RSVD | JIT scratchpad

 * current ARM_SP =>      +-----+ <= (BPF_FP - STACK_SIZE)

 * current ARM_SP =>      +-----+ <= (BPF_FP - STACK_SIZE + SCRATCH_SIZE)

 *                        |     |

 *                        | ... | Function call stack

 *                        |     |

 *                        +-----+

 *                          low

 *

 * The callee saved registers depends on whether frame pointers are enabled.

 * With frame pointers (to be compliant with the ABI):

 *

 *                                high

 * original ARM_SP =>     +------------------+ \

 *                        |        pc        | |

 * current ARM_FP =>      +------------------+ } callee saved registers

 *                        |r4-r8,r10,fp,ip,lr| |

 *                        +------------------+ /

 *                                low

 *

 * Without frame pointers:

 *

 *                                high

 * original ARM_SP =>     +------------------+

 *                        |        lr        | (optional)

 *                        |     r4-r8,r10    | callee saved registers

 *                        +------------------+

 *                                low

 */



#define STACK_OFFSET(k)	(k)