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On 27/9/24 07:45, Yonghong Song wrote: > Add jit support for private stack. For a particular subtree, e.g., > subtree_root <== stack depth 120 > subprog1 <== stack depth 80 > subprog2 <== stack depth 40 > subprog3 <== stack depth 160 > > Let us say that private_stack_ptr is the memory address allocated for > private stack. The frame pointer for each above is calculated like below: > subtree_root <== subtree_root_fp = private_stack_ptr + 120 > subprog1 <== subtree_subprog1_fp = subtree_root_fp + 80 > subprog2 <== subtree_subprog2_fp = subtree_subprog1_fp + 40 > subprog3 <== subtree_subprog1_fp = subtree_root_fp + 160 > > For any function call to helper/kfunc, push/pop prog frame pointer > is needed in order to preserve frame pointer value. > > To deal with exception handling, push/pop frame pointer is also used > surrounding call to subsequent subprog. For example, > subtree_root > subprog1 > ... > insn: call bpf_throw > ... > > After jit, we will have > subtree_root > insn: push r9 > subprog1 > ... > insn: push r9 > insn: call bpf_throw > insn: pop r9 > ... > insn: pop r9 > > exception_handler > pop r9 > ... > where r9 represents the fp for each subprog. > > Signed-off-by: Yonghong Song > --- > arch/x86/net/bpf_jit_comp.c | 87 ++++++++++++++++++++++++++++++++++--- > 1 file changed, 81 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c > index 06b080b61aa5..c264822c926b 100644 > --- a/arch/x86/net/bpf_jit_comp.c > +++ b/arch/x86/net/bpf_jit_comp.c > @@ -325,6 +325,22 @@ struct jit_context { > /* Number of bytes that will be skipped on tailcall */ > #define X86_TAIL_CALL_OFFSET (12 + ENDBR_INSN_SIZE) > > +static void push_r9(u8 **pprog) > +{ > + u8 *prog = *pprog; > + > + EMIT2(0x41, 0x51); /* push r9 */ > + *pprog = prog; > +} > + > +static void pop_r9(u8 **pprog) > +{ > + u8 *prog = *pprog; > + > + EMIT2(0x41, 0x59); /* pop r9 */ > + *pprog = prog; > +} > + > static void push_r12(u8 **pprog) > { > u8 *prog = *pprog; > @@ -491,7 +507,7 @@ static void emit_prologue_tail_call(u8 **pprog, bool is_subprog) > */ > static void emit_prologue(u8 **pprog, u32 stack_depth, bool ebpf_from_cbpf, > bool tail_call_reachable, bool is_subprog, > - bool is_exception_cb) > + bool is_exception_cb, enum bpf_pstack_state pstack) > { > u8 *prog = *pprog; > > @@ -518,6 +534,8 @@ static void emit_prologue(u8 **pprog, u32 stack_depth, bool ebpf_from_cbpf, > * first restore those callee-saved regs from stack, before > * reusing the stack frame. > */ > + if (pstack) > + pop_r9(&prog); > pop_callee_regs(&prog, all_callee_regs_used); > pop_r12(&prog); > /* Reset the stack frame. */ > @@ -1404,6 +1422,22 @@ static void emit_shiftx(u8 **pprog, u32 dst_reg, u8 src_reg, bool is64, u8 op) > *pprog = prog; > } > > +static void emit_private_frame_ptr(u8 **pprog, void *private_frame_ptr) > +{ > + u8 *prog = *pprog; > + > + /* movabs r9, private_frame_ptr */ > + emit_mov_imm64(&prog, X86_REG_R9, (long) private_frame_ptr >> 32, > + (u32) (long) private_frame_ptr); > + > + /* add , gs:[] */ > + EMIT2(0x65, 0x4c); > + EMIT3(0x03, 0x0c, 0x25); > + EMIT((u32)(unsigned long)&this_cpu_off, 4); It should check CONFIG_SMP here like this commit: 1e9e0b85255e ("bpf: handle CONFIG_SMP=n configuration in x86 BPF JIT"). So, it seems better to reuse the code snippet of the commit. Thanks, Leon