diff options
| author | Russell King <rmk+kernel@armlinux.org.uk> | 2018-01-13 22:51:27 +0000 |
|---|---|---|
| committer | Russell King <rmk+kernel@armlinux.org.uk> | 2018-01-17 19:36:43 +0000 |
| commit | 0005e55a79cfda88199e41a406a829c88d708c67 (patch) | |
| tree | 7b7c6773a85dce1f352ad2a12232d781ac1bcc38 /arch/arm/net | |
| parent | 70ec3a6c2c11e4b0e107a65de943a082f9aff351 (diff) | |
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: Russell King <rmk+kernel@armlinux.org.uk>
Diffstat (limited to 'arch/arm/net')
| -rw-r--r-- | arch/arm/net/bpf_jit_32.c | 35 |
1 files changed, 27 insertions, 8 deletions
diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c index e90229d58c77..dcb3181e85f3 100644 --- a/arch/arm/net/bpf_jit_32.c +++ b/arch/arm/net/bpf_jit_32.c @@ -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) |