Messages in this thread Patch in this message | | | Date | Thu, 15 Oct 2015 19:56:55 +0800 | From | "Wangnan (F)" <> | Subject | Re: [PATCH 16/31] perf tools: Add prologue for BPF programs for fetching arguments |
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On 2015/10/15 13:26, Namhyung Kim wrote: > On Wed, Oct 14, 2015 at 12:41:27PM +0000, Wang Nan wrote: >> From: He Kuang <hekuang@huawei.com> >> >> This patch generates prologue for a BPF program which fetch arguments >> for it. With this patch, the program can have arguments as follow: >> >> SEC("lock_page=__lock_page page->flags") >> int lock_page(struct pt_regs *ctx, int err, unsigned long flags) >> { >> return 1; >> } >> >> This patch passes at most 3 arguments from r3, r4 and r5. r1 is still >> the ctx pointer. r2 is used to indicate the successfulness of >> dereferencing. >> >> This patch uses r6 to hold ctx (struct pt_regs) and r7 to hold stack >> pointer for result. Result of each arguments first store on stack: >> >> low address >> BPF_REG_FP - 24 ARG3 >> BPF_REG_FP - 16 ARG2 >> BPF_REG_FP - 8 ARG1 >> BPF_REG_FP >> high address >> >> Then loaded into r3, r4 and r5. >> >> The output prologue for offn(...off2(off1(reg)))) should be: >> >> r6 <- r1 // save ctx into a callee saved register >> r7 <- fp >> r7 <- r7 - stack_offset // pointer to result slot >> /* load r3 with the offset in pt_regs of 'reg' */ >> (r7) <- r3 // make slot valid >> r3 <- r3 + off1 // prepare to read unsafe pointer >> r2 <- 8 >> r1 <- r7 // result put onto stack >> call probe_read // read unsafe pointer >> jnei r0, 0, err // error checking >> r3 <- (r7) // read result >> r3 <- r3 + off2 // prepare to read unsafe pointer >> r2 <- 8 >> r1 <- r7 >> call probe_read >> jnei r0, 0, err >> ... >> /* load r2, r3, r4 from stack */ >> goto success >> err: >> r2 <- 1 >> /* load r3, r4, r5 with 0 */ >> goto usercode >> success: >> r2 <- 0 >> usercode: >> r1 <- r6 // restore ctx >> // original user code >> >> If all of arguments reside in register (dereferencing is not >> required), gen_prologue_fastpath() will be used to create >> fast prologue: >> >> r3 <- (r1 + offset of reg1) >> r4 <- (r1 + offset of reg2) >> r5 <- (r1 + offset of reg3) >> r2 <- 0 >> >> P.S. >> >> eBPF calling convention is defined as: >> >> * r0 - return value from in-kernel function, and exit value >> for eBPF program >> * r1 - r5 - arguments from eBPF program to in-kernel function >> * r6 - r9 - callee saved registers that in-kernel function will >> preserve >> * r10 - read-only frame pointer to access stack >> >> Signed-off-by: He Kuang <hekuang@huawei.com> >> Signed-off-by: Wang Nan <wangnan0@huawei.com> >> Cc: Alexei Starovoitov <ast@plumgrid.com> >> Cc: Brendan Gregg <brendan.d.gregg@gmail.com> >> Cc: Daniel Borkmann <daniel@iogearbox.net> >> Cc: David Ahern <dsahern@gmail.com> >> Cc: He Kuang <hekuang@huawei.com> >> Cc: Jiri Olsa <jolsa@kernel.org> >> Cc: Kaixu Xia <xiakaixu@huawei.com> >> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> >> Cc: Namhyung Kim <namhyung@kernel.org> >> Cc: Paul Mackerras <paulus@samba.org> >> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> >> Cc: Zefan Li <lizefan@huawei.com> >> Cc: pi3orama@163.com >> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> >> Link: http://lkml.kernel.org/n/ebpf-6yw9eg0ej3l4jnqhinngkw86@git.kernel.org >> --- > [SNIP] >> +int bpf__gen_prologue(struct probe_trace_arg *args, int nargs, >> + struct bpf_insn *new_prog, size_t *new_cnt, >> + size_t cnt_space) >> +{ >> + struct bpf_insn *success_code = NULL; >> + struct bpf_insn *error_code = NULL; >> + struct bpf_insn *user_code = NULL; >> + struct bpf_insn_pos pos; >> + bool fastpath = true; >> + int i; >> + >> + if (!new_prog || !new_cnt) >> + return -EINVAL; >> + >> + pos.begin = new_prog; >> + pos.end = new_prog + cnt_space; >> + pos.pos = new_prog; >> + >> + if (!nargs) { >> + ins(BPF_ALU64_IMM(BPF_MOV, BPF_PROLOGUE_FETCH_RESULT_REG, 0), >> + &pos); >> + >> + if (check_pos(&pos)) >> + goto errout; >> + >> + *new_cnt = pos_get_cnt(&pos); >> + return 0; >> + } >> + >> + if (nargs > BPF_PROLOGUE_MAX_ARGS) >> + nargs = BPF_PROLOGUE_MAX_ARGS; > Wouldn't it be better to inform user if it ignored some arguments?
Correct. I'd like to add a notification in next version:
diff --git a/tools/perf/util/bpf-prologue.c b/tools/perf/util/bpf-prologue.c index e4adb18..36093d9 100644 --- a/tools/perf/util/bpf-prologue.c +++ b/tools/perf/util/bpf-prologue.c @@ -337,8 +337,10 @@ int bpf__gen_prologue(struct probe_trace_arg *args, int nargs, return 0; }
- if (nargs > BPF_PROLOGUE_MAX_ARGS) + if (nargs > BPF_PROLOGUE_MAX_ARGS) { + pr_warning("bpf: prologue: too many arguments\n"); nargs = BPF_PROLOGUE_MAX_ARGS; + } if (cnt_space > BPF_MAXINSNS) cnt_space = BPF_MAXINSNS;
Thank you.
> Thanks, > Namhyung
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