From: Yonghong Song yhs@fb.com
mainline inclusion from mainline-v6.1-rc1 commit a9c5ad31fbdc4dec6d266fe22e51de1ad6d1bcf2 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I9FGRE
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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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@fb.com Link: https://lore.kernel.org/r/20220831152652.2078600-1-yhs@fb.com Signed-off-by: Alexei Starovoitov ast@kernel.org Conflicts: arch/x86/net/bpf_jit_comp.c Signed-off-by: Pu Lehui pulehui@huawei.com --- arch/x86/net/bpf_jit_comp.c | 60 +++++++++++++++++++++++++++++-------- 1 file changed, 47 insertions(+), 13 deletions(-)
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 8e3c3d8916dd..39265694f507 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -1510,34 +1510,60 @@ xadd: 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]; + } + + while (nr_regs) { + emit_stx(prog, bytes_to_bpf_size(arg_size), + BPF_REG_FP, + j == 5 ? X86_REG_R9 : BPF_REG_1 + j, + -(stack_size - j * 8)); + nr_regs--; + j++; + } + } }
static void restore_regs(const struct btf_func_model *m, u8 **prog, int nr_args, int stack_size) { - int i; + int i, j, arg_size, nr_regs;
/* Restore function arguments from stack. * For a function that accepts two pointers the sequence will be: * EMIT4(0x48, 0x8B, 0x7D, 0xF0); mov rdi,QWORD PTR [rbp-0x10] * EMIT4(0x48, 0x8B, 0x75, 0xF8); mov rsi,QWORD PTR [rbp-0x8] */ - for (i = 0; i < min(nr_args, 6); i++) - emit_ldx(prog, bytes_to_bpf_size(m->arg_size[i]), - i == 5 ? X86_REG_R9 : BPF_REG_1 + i, - BPF_REG_FP, - -(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]; + } + + while (nr_regs) { + emit_ldx(prog, bytes_to_bpf_size(arg_size), + j == 5 ? X86_REG_R9 : BPF_REG_1 + j, + BPF_REG_FP, + -(stack_size - j * 8)); + nr_regs--; + j++; + } + } }
static int invoke_bpf_prog(const struct btf_func_model *m, u8 **pprog, @@ -1776,7 +1802,7 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i struct bpf_tramp_progs *tprogs, void *orig_call) { - int ret, i, cnt = 0, nr_args = m->nr_args; + int ret, i, cnt = 0, nr_args = m->nr_args, extra_nregs = 0; int stack_size = nr_args * 8; struct bpf_tramp_progs *fentry = &tprogs[BPF_TRAMP_FENTRY]; struct bpf_tramp_progs *fexit = &tprogs[BPF_TRAMP_FEXIT]; @@ -1789,6 +1815,14 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i if (nr_args > 6) return -ENOTSUPP;
+ for (i = 0; i < MAX_BPF_FUNC_ARGS; i++) { + if (m->arg_flags[i] & BTF_FMODEL_STRUCT_ARG) + extra_nregs += (m->arg_size[i] + 7) / 8 - 1; + } + if (nr_args + extra_nregs > 6) + return -ENOTSUPP; + stack_size += extra_nregs * 8; + if (!is_valid_bpf_tramp_flags(flags)) return -EINVAL;