[DTrace-devel] [PATCH v3 02/19] cg: add dt_cg_trace

[Kris Van Hees]

I am going to leave review of this patch for after the alloca series itself is
completed because it is not a necessary patch in that series.  Eugene expressed
the same notion, and I also agree that the interface may benefit from some
tweaking.

On Thu, Mar 24, 2022 at 06:24:28PM +0000, Nick Alcock via DTrace-devel wrote:
> A call to
> 
>    dt_cg_trace(dlp, drp, 1, 666, foo);
> 
> will trace the value of reg FOO into
> /sys/kernel/debug/tracing/trace_pipe when dtrace is compiled with
> debugging=yes.  '666' above is a counter value which is also logged in
> the resulting trace output, to distinguish trace calls from each other.
> 
> A call to
> 
>   dt_cg_trace(dlp, drp, 0, 666, foo);
> 
> will trace the immediate value of FOO at codegen time.
> 
> Under debugging=no this call has no effect and is compiled out.
> 
> Signed-off-by: Nick Alcock <nick.alcock at oracle.com>
> ---
>  Makeoptions       |  3 ++-
>  bpf/Build         |  3 ++-
>  bpf/trace_ptr.c   | 23 +++++++++++++++++++++++
>  libdtrace/dt_cg.c | 30 ++++++++++++++++++++++++++++++
>  4 files changed, 57 insertions(+), 2 deletions(-)
>  create mode 100644 bpf/trace_ptr.c
> 
> diff --git a/Makeoptions b/Makeoptions
> index 011440a31d83..dba38641154f 100644
> --- a/Makeoptions
> +++ b/Makeoptions
> @@ -17,7 +17,8 @@ help::
>  	@printf "\n" >&2
>  
>  ifneq ($(debugging),no)
> -override CFLAGS += -O0 -g
> +override CFLAGS += -O0 -g -DDEBUGGING
> +override BPFCFLAGS += -DDEBUGGING
>  endif
>  
>  ifneq ($(coverage),no)
> diff --git a/bpf/Build b/bpf/Build
> index d986fd7e089b..1540382bc322 100644
> --- a/bpf/Build
> +++ b/bpf/Build
> @@ -38,7 +38,8 @@ bpf_dlib_SOURCES = \
>  	strlen.c \
>  	strrchr.S \
>  	strtok.S \
> -	substr.S
> +	substr.S \
> +	trace_ptr.c
>  
>  bpf-check: $(objdir)/include/.dir.stamp
>  	$(BPFC) $(BPFCPPFLAGS) $(bpf_dlib_CPPFLAGS) $(BPFCFLAGS) -S \
> diff --git a/bpf/trace_ptr.c b/bpf/trace_ptr.c
> new file mode 100644
> index 000000000000..9dcbc720a115
> --- /dev/null
> +++ b/bpf/trace_ptr.c
> @@ -0,0 +1,23 @@
> +#ifdef DEBUGGING
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2021, Oracle and/or its affiliates. All rights reserved.
> + */
> +#include <linux/bpf.h>
> +#include <stdint.h>
> +#include <bpf-helpers.h>
> +
> +#ifndef noinline
> +# define noinline	__attribute__((noinline))
> +#endif
> +
> +noinline void dt_trace_ptr(uint64_t counter, uint64_t ptr)
> +{
> +	/*
> +	 * Can't use a straight string constant: DTrace cannot yet process
> +	 * rodata relocs.
> +	 */
> +	char fmt[] = "debug: %d: %lx\n";
> +	bpf_trace_printk(fmt, 16, counter, ptr);
> +}
> +#endif
> diff --git a/libdtrace/dt_cg.c b/libdtrace/dt_cg.c
> index a149c57529f1..5f86c34d7be4 100644
> --- a/libdtrace/dt_cg.c
> +++ b/libdtrace/dt_cg.c
> @@ -25,6 +25,9 @@
>  #include <bpf_asm.h>
>  
>  static void dt_cg_node(dt_node_t *, dt_irlist_t *, dt_regset_t *);
> +static void _dt_unused_
> +dt_cg_trace(dt_irlist_t *dlp _dt_unused_, dt_regset_t *drp _dt_unused_,
> +	    int isreg _dt_unused_, int counter _dt_unused_, uint64_t val _dt_unused_);
>  
>  /*
>   * Generate the generic prologue of the trampoline BPF program.
> @@ -744,6 +747,33 @@ dt_cg_fill_gap(dt_pcb_t *pcb, int gap)
>  		emit(dlp, BPF_STORE_IMM(BPF_W, BPF_REG_9, off, 0));
>  }
>  
> +/*
> + * Trace an immediate counter and a value to the log at
> + * /sys/kernel/debug/tracing/trace_pipe.  If ISREG, VAL is a register number:
> + * otherwise, it's an immediate value.
> + */
> +static void _dt_unused_
> +dt_cg_trace(dt_irlist_t *dlp _dt_unused_, dt_regset_t *drp _dt_unused_,
> +	    int isreg _dt_unused_, int counter _dt_unused_, uint64_t val _dt_unused_)
> +{
> +#ifdef DEBUGGING
> +	dt_ident_t	*idp = dt_dlib_get_func(yypcb->pcb_hdl, "dt_trace_ptr");
> +
> +	if (dt_regset_xalloc_args(drp) == -1)
> +		longjmp(yypcb->pcb_jmpbuf, EDT_NOREG);
> +	dt_regset_xalloc(drp, BPF_REG_0);
> +	emit(dlp,  BPF_MOV_IMM(BPF_REG_1, counter));
> +	if (isreg)
> +		emit(dlp,  BPF_MOV_REG(BPF_REG_2, val));
> +	else
> +		emit(dlp,  BPF_MOV_IMM(BPF_REG_2, val));
> +
> +	emite(dlp, BPF_CALL_FUNC(idp->di_id), idp);
> +	dt_regset_free(drp, BPF_REG_0);
> +	dt_regset_free_args(drp);
> +#endif
> +}
> +
>  static void
>  dt_cg_memcpy(dt_irlist_t *dlp, dt_regset_t *drp, int dst, int src, size_t size)
>  {
> -- 
> 2.35.1.261.g8402f930ba.dirty
> 
> 
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