linux-kernel - Re: [PATCH] perf bpf: Fix endianness problem when loading parameters in prologue

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Message-ID: <20170811192344.GA6073@kernel.org>
Date:   Fri, 11 Aug 2017 16:23:44 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Thomas-Mich Richter <tmricht@...ux.vnet.ibm.com>,
        "Wangnan (F)" <wangnan0@...wei.com>
Cc:     tmricht@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
        Li Zefan <lizefan@...wei.com>
Subject: Re: [PATCH] perf bpf: Fix endianness problem when loading parameters
 in prologue

Em Fri, Aug 11, 2017 at 06:47:56PM +0800, Wangnan (F) escreveu:
> Hi Thomas,
> 
> Please try this patch on your machine and give me the result.

Right, I'm waiting for test results for the last two patches from Wang:

      (3.0K) [PATCH] perf bpf: Fix endianness problem when loading parameters in prologue
      (1.2K) [PATCH] perf test llvm: Fix f_mode endianness problem

Thanks,

- Arnaldo
 
> Thank you.
> 
> On 2017/8/13 2:49, Wang Nan wrote:
> > Perf BPF prologue generator unconditionally fetches 8 bytes for function
> > parameters, which causes problem on big endian machine. Thomas gives a
> > detail analysis for this problem:
> > 
> >   http://lkml.kernel.org/r/968ebda5-abe4-8830-8d69-49f62529d151@linux.vnet.ibm.com
> > 
> > This patch parses the type of each argument and converts data from
> > memory to expected type.
> > 
> > Signed-off-by: Wang Nan <wangnan0@...wei.com>
> > Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> > Cc: Thomas Richter <tmricht@...ux.vnet.ibm.com>
> > Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>
> > Cc: Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>
> > Cc: Li Zefan <lizefan@...wei.com>
> > ---
> >   tools/perf/tests/bpf-script-test-prologue.c |  4 ++-
> >   tools/perf/util/bpf-prologue.c              | 49 +++++++++++++++++++++++++++--
> >   2 files changed, 50 insertions(+), 3 deletions(-)
> > 
> > diff --git a/tools/perf/tests/bpf-script-test-prologue.c b/tools/perf/tests/bpf-script-test-prologue.c
> > index b4ebc75..43f1e16 100644
> > --- a/tools/perf/tests/bpf-script-test-prologue.c
> > +++ b/tools/perf/tests/bpf-script-test-prologue.c
> > @@ -26,9 +26,11 @@ static void (*bpf_trace_printk)(const char *fmt, int fmt_size, ...) =
> >   	(void *) 6;
> >   SEC("func=null_lseek file->f_mode offset orig")
> > -int bpf_func__null_lseek(void *ctx, int err, unsigned long f_mode,
> > +int bpf_func__null_lseek(void *ctx, int err, unsigned long _f_mode,
> >   			 unsigned long offset, unsigned long orig)
> >   {
> > +	fmode_t f_mode = (fmode_t)_f_mode;
> > +
> >   	if (err)
> >   		return 0;
> >   	if (f_mode & FMODE_WRITE)
> > diff --git a/tools/perf/util/bpf-prologue.c b/tools/perf/util/bpf-prologue.c
> > index 6cdbee1..ce28993 100644
> > --- a/tools/perf/util/bpf-prologue.c
> > +++ b/tools/perf/util/bpf-prologue.c
> > @@ -57,6 +57,46 @@ check_pos(struct bpf_insn_pos *pos)
> >   	return 0;
> >   }
> > +/*
> > + * Convert type string (u8/u16/u32/u64/s8/s16/s32/s64 ..., see
> > + * Documentation/trace/kprobetrace.txt) to size field of BPF_LDX_MEM
> > + * instruction (BPF_{B,H,W,DW}).
> > + */
> > +static int
> > +argtype_to_ldx_size(const char *type)
> > +{
> > +	int arg_size = type ? atoi(&type[1]) : 64;
> > +
> > +	switch (arg_size) {
> > +	case 8:
> > +		return BPF_B;
> > +	case 16:
> > +		return BPF_H;
> > +	case 32:
> > +		return BPF_W;
> > +	case 64:
> > +	default:
> > +		return BPF_DW;
> > +	}
> > +}
> > +
> > +static const char *
> > +insn_sz_to_str(int insn_sz)
> > +{
> > +	switch (insn_sz) {
> > +	case BPF_B:
> > +		return "BPF_B";
> > +	case BPF_H:
> > +		return "BPF_H";
> > +	case BPF_W:
> > +		return "BPF_W";
> > +	case BPF_DW:
> > +		return "BPF_DW";
> > +	default:
> > +		return "UNKNOWN";
> > +	}
> > +}
> > +
> >   /* Give it a shorter name */
> >   #define ins(i, p) append_insn((i), (p))
> > @@ -257,9 +297,14 @@ gen_prologue_slowpath(struct bpf_insn_pos *pos,
> >   	}
> >   	/* Final pass: read to registers */
> > -	for (i = 0; i < nargs; i++)
> > -		ins(BPF_LDX_MEM(BPF_DW, BPF_PROLOGUE_START_ARG_REG + i,
> > +	for (i = 0; i < nargs; i++) {
> > +		int insn_sz = argtype_to_ldx_size(args[i].type);
> > +
> > +		pr_debug("prologue: load arg %d, insn_sz is %s\n",
> > +			 i, insn_sz_to_str(insn_sz));
> > +		ins(BPF_LDX_MEM(insn_sz, BPF_PROLOGUE_START_ARG_REG + i,
> >   				BPF_REG_FP, -BPF_REG_SIZE * (i + 1)), pos);
> > +	}
> >   	ins(BPF_JMP_IMM(BPF_JA, BPF_REG_0, 0, JMP_TO_SUCCESS_CODE), pos);
>