On Wed, Aug 31, 2022 at 8:26 AM Yonghong Song <yhs@xxxxxx> wrote: > > In C, struct value can be passed as a function argument. > For small structs, struct value may be passed in > one or more registers. For trampoline based bpf programs, > this would cause complication since one-to-one mapping between > function argument and arch argument register is not valid > any more. > > The latest llvm16 added bpf support to pass by values > for struct up to 16 bytes ([1]). This is also true for > x86_64 architecture where two registers will hold > the struct value if the struct size is >8 and <= 16. > This may not be true if one of struct member is 'double' > type but in current linux source code we don't have > such instance yet, so we assume all >8 && <= 16 struct > holds two general purpose argument registers. > > Also change on-stack nr_args value to the number > of registers holding the arguments. This will > permit bpf_get_func_arg() helper to get all > argument values. > > [1] https://reviews.llvm.org/D132144 > > Signed-off-by: Yonghong Song <yhs@xxxxxx> > --- > arch/x86/net/bpf_jit_comp.c | 68 +++++++++++++++++++++++++++---------- > 1 file changed, 51 insertions(+), 17 deletions(-) > > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c > index c1f6c1c51d99..ae89f4143eb4 100644 > --- a/arch/x86/net/bpf_jit_comp.c > +++ b/arch/x86/net/bpf_jit_comp.c > @@ -1751,34 +1751,60 @@ st: if (is_imm8(insn->off)) > static void save_regs(const struct btf_func_model *m, u8 **prog, int nr_args, > int stack_size) > { > - int i; > + int i, j, arg_size, nr_regs; > /* Store function arguments to stack. > * For a function that accepts two pointers the sequence will be: > * mov QWORD PTR [rbp-0x10],rdi > * mov QWORD PTR [rbp-0x8],rsi > */ > - for (i = 0; i < min(nr_args, 6); i++) > - emit_stx(prog, bytes_to_bpf_size(m->arg_size[i]), > - BPF_REG_FP, > - i == 5 ? X86_REG_R9 : BPF_REG_1 + i, > - -(stack_size - i * 8)); > + for (i = 0, j = 0; i < min(nr_args, 6); i++) { > + if (m->arg_flags[i] & BTF_FMODEL_STRUCT_ARG) { > + nr_regs = (m->arg_size[i] + 7) / 8; > + arg_size = 8; > + } else { > + nr_regs = 1; > + arg_size = m->arg_size[i]; > + } This bit begs for a common helper, but I'm not sure whether it will look better, so applied as-is. BPF_PROG2 also feels unusual as an API macro name. We probably should bikeshed a bit and follow up if a better name is found.
