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Re: [PATCH 3/3] Convert DTrace probe interface to C++ (and perform some cleanups)
On Tuesday, November 14 2017, Simon Marchi wrote:
> Hi Sergio,
Hey Simon,
Thanks for the review.
> On 2017-11-13 12:59 PM, Sergio Durigan Junior wrote:
>> This patch converts the DTrace probe
>> interface (gdb/dtrace-probe.[ch]) to C++, and also performs some
>> cleanups that were on my TODO list for a while.
>>
>> The main changes were the conversion of 'struct dtrace_probe' to 'class
>> dtrace_probe', and a new 'class dtrace_static_probe_ops' to replace the
>> use of 'dtrace_probe_ops'. Both classes implement the virtual methods
>> exported by their parents, 'class probe' and 'class static_probe_ops',
>> respectively. I believe it's now a bit simpler to understand the
>> logic behind the dtrace-probe interface.
>>
>> There are several helper functions used to parse parts of a dtrace
>> probe, and since they are generic and don't need to know about the
>> probe they're working on, I decided to leave them as simple static
>> functions (instead of e.g. converting them to class methods).
>>
>> I've also converted a few uses of "VEC" to "std::vector", which makes
>> the code simpler and easier to maintain. And, as usual, some cleanups
>> here and there.
>>
>> Even though I'm sending a series of patches, they need to be tested
>> and committed as a single unit, because of inter-dependencies. But it
>> should be easier to review in separate logical units.
>>
>> I've regtested this patch on BuildBot, no regressions found.
>>
>> gdb/ChangeLog:
>> 2017-11-13 Sergio Durigan Junior <sergiodj@redhat.com>
>>
>> * dtrace-probe.c (struct probe_ops dtrace_probe_ops): Delete.
>> (dtrace_probe_arg_s): Delete type and VEC.
>> (dtrace_probe_enabler_s): Likewise.
>> (struct dtrace_probe): Replace by...
>> (class dtrace_static_probe_ops): ...this and...
>> (class dtrace_probe): ...this.
>> (dtrace_probe_is_linespec): Rename to...
>> (dtrace_static_probe_ops::is_linespec): ...this. Adjust code
>> to reflect change.
>> (dtrace_process_dof_probe): Use 'std::vector' instead of VEC.
>> Adjust code. Create new instance of 'dtrace_probe'.
>> (dtrace_build_arg_exprs): Rename to...
>> (dtrace_probe::build_arg_exprs): ...this. Adjust code to
>> reflect change.
>> (dtrace_get_probes): Rename to...
>> (dtrace_static_probe_ops::get_probes): ...this. Adjust code
>> to reflect change.
>> (dtrace_get_arg): Rename to...
>> (dtrace_probe::get_arg_by_number): ...this. Adjust code to
>> reflect change.
>> (dtrace_probe_is_enabled): Rename to...
>> (dtrace_probe::is_enabled): ...this. Adjust code to reflect
>> change.
>> (dtrace_get_probe_address): Rename to...
>> (dtrace_probe::get_relocated_address): ...this. Adjust code
>> to reflect change.
>> (dtrace_get_probe_argument_count): Rename to...
>> (dtrace_probe::get_argument_count): ...this. Adjust code to
>> reflect change.
>> (dtrace_can_evaluate_probe_arguments): Rename to...
>> (dtrace_probe::can_evaluate_arguments): ...this. Adjust code
>> to reflect change.
>> (dtrace_evaluate_probe_argument): Rename to...
>> (dtrace_probe::evaluate_argument): ...this. Adjust code to
>> reflect change.
>> (dtrace_compile_to_ax): Rename to...
>> (dtrace_probe::compile_to_ax): ...this. Adjust code to
>> reflect change.
>> (dtrace_probe_destroy): Delete.
>> (dtrace_type_name): Rename to...
>> (dtrace_static_probe_ops::type_name): ...this. Adjust code to
>> reflect change.
>> (dtrace_probe::get_static_ops): New method.
>> (dtrace_gen_info_probes_table_header): Rename to...
>> (dtrace_static_probe_ops::gen_info_probes_table_header):
>> ...this. Adjust code to reflect change.
>> (dtrace_gen_info_probes_table_values): Rename to...
>> (dtrace_probe::gen_info_probes_table_values): ...this. Adjust
>> code to reflect change.
>> (dtrace_enable_probe): Rename to...
>> (dtrace_probe::enable_probe): ...this. Adjust code to reflect
>> change.
>> (dtrace_disable_probe): Rename to...
>> (dtrace_probe::disable_probe): ...this. Adjust code to reflect
>> change.
>> (struct probe_ops dtrace_probe_ops): Delete.
>> (dtrace_static_probe_ops::emit_info_probes_extra_fields): New
>> method.
>> (info_probes_dtrace_command): Call 'info_probes_for_spops'
>> instead of 'info_probes_for_ops'.
>> (_initialize_dtrace_probe): Use 'all_static_probe_ops' instead
>> of 'all_probe_ops'.
>> ---
>> gdb/dtrace-probe.c | 528 +++++++++++++++++++++++++++--------------------------
>> 1 file changed, 268 insertions(+), 260 deletions(-)
>>
>> diff --git a/gdb/dtrace-probe.c b/gdb/dtrace-probe.c
>> index 2bbe03e4b3..b53ff7ac6c 100644
>> --- a/gdb/dtrace-probe.c
>> +++ b/gdb/dtrace-probe.c
>> @@ -41,10 +41,6 @@
>> # define SHT_SUNW_dof 0x6ffffff4
>> #endif
>>
>> -/* Forward declaration. */
>> -
>> -extern const struct probe_ops dtrace_probe_ops;
>> -
>> /* The following structure represents a single argument for the
>> probe. */
>>
>> @@ -60,9 +56,6 @@ struct dtrace_probe_arg
>> struct expression *expr;
>> };
>>
>> -typedef struct dtrace_probe_arg dtrace_probe_arg_s;
>> -DEF_VEC_O (dtrace_probe_arg_s);
>> -
>> /* The following structure represents an enabler for a probe. */
>>
>> struct dtrace_probe_enabler
>> @@ -73,39 +66,121 @@ struct dtrace_probe_enabler
>> CORE_ADDR address;
>> };
>>
>> -typedef struct dtrace_probe_enabler dtrace_probe_enabler_s;
>> -DEF_VEC_O (dtrace_probe_enabler_s);
>> +/* Class that implements the static probe methods for "stap" probes. */
>> +
>> +class dtrace_static_probe_ops : public static_probe_ops
>> +{
>> +public:
>> + /* See probe.h. */
>> + bool is_linespec (const char **linespecp) const override;
>> +
>> + /* See probe.h. */
>> + void get_probes (std::vector<probe *> *probesp,
>> + struct objfile *objfile) const override;
>> +
>> + /* See probe.h. */
>> + const char *type_name () const override;
>> +
>> + /* See probe.h. */
>> + bool emit_info_probes_extra_fields () const override;
>> +
>> + /* See probe.h. */
>> + void gen_info_probes_table_header
>> + (std::vector<struct info_probe_column> *heads) const override;
>> +};
>> +
>> +/* DTrace static_probe_ops. */
>> +
>> +const dtrace_static_probe_ops dtrace_static_probe_ops;
>>
>> /* The following structure represents a dtrace probe. */
>>
>> -struct dtrace_probe
>> +class dtrace_probe : public probe
>> {
>> - /* Generic information about the probe. This must be the first
>> - element of this struct, in order to maintain binary compatibility
>> - with the `struct probe' and be able to fully abstract it. */
>> - struct probe p;
>> +public:
>> + /* Constructor for dtrace_probe. */
>> + dtrace_probe (std::string &&name_, std::string &&provider_, CORE_ADDR address_,
>> + struct gdbarch *arch_,
>> + std::vector<struct dtrace_probe_arg> &args_,
>> + std::vector<struct dtrace_probe_enabler> &enablers_)
>
> I am wondering why you don't use && for the vectors, as you do with the strings.
> If the constructor is "stealing" from the vectors passed as parameter, I think it
> would make sense if the parameters were &&, to indicate to the caller that they'll
> be moved from (and force it to use std::move).
That's true. I think I was misunderstanding the relationship between
rvalues, lvalues and &&. Fixed.
>> + : probe (std::move (name_), std::move (provider_), address_, arch_),
>> + m_args (std::move (args_)),
>> + m_enablers (std::move (enablers_)),
>> + m_args_expr_built (false)
>> + {}
>> +
>> + /* Destructor for dtrace_probe. */
>> + ~dtrace_probe ()
>> + {
>> + for (struct dtrace_probe_arg arg : m_args)
>> + {
>> + xfree (arg.type_str);
>> + xfree (arg.expr);
>> + }
>
> As for stap_probe, I think defining a destructor in dtrace_probe_arg would
> be clearer.
I used the same approach as in stap-probe.c: expression_up,
emplace_back, a constructor that takes care of std::move'ing things, and
no destructor. I also converted 'type_str' to std::string.
>> + }
>> +
>> + /* See probe.h. */
>> + CORE_ADDR get_relocated_address (struct objfile *objfile) override;
>> +
>> + /* See probe.h. */
>> + unsigned get_argument_count (struct frame_info *frame) override;
>> +
>> + /* See probe.h. */
>> + int can_evaluate_arguments () const override;
>> +
>> + /* See probe.h. */
>> + struct value *evaluate_argument (unsigned n,
>> + struct frame_info *frame) override;
>> +
>> + /* See probe.h. */
>> + void compile_to_ax (struct agent_expr *aexpr,
>> + struct axs_value *axs_value,
>> + unsigned n) override;
>> +
>> + /* See probe.h. */
>> + const static_probe_ops *get_static_ops () const override;
>> +
>> + /* See probe.h. */
>> + void gen_info_probes_table_values
>> + (std::vector<const char *> *values) const override;
>> +
>> + /* See probe.h. */
>> + bool can_enable () const override
>> + {
>> + return true;
>> + }
>> +
>> + /* See probe.h. */
>> + void enable () override;
>>
>> + /* See probe.h. */
>> + void disable () override;
>> +
>> + /* Return the Nth argument of the probe. */
>> + struct dtrace_probe_arg *get_arg_by_number (unsigned n,
>> + struct gdbarch *gdbarch);
>> +
>> + /* Build the GDB internal expressiosn that, once evaluated, will
>> + calculate the values of the arguments of the probe. */
>> + void build_arg_exprs (struct gdbarch *gdbarch);
>> +
>> + /* Determine whether the probe is "enabled" or "disabled". A
>> + disabled probe is a probe in which one or more enablers are
>> + disabled. */
>> + bool is_enabled () const;
>> +
>> +private:
>> /* A probe can have zero or more arguments. */
>> - int probe_argc;
>> - VEC (dtrace_probe_arg_s) *args;
>> + int m_argc;
>
> It seems like this field is never set, but used at least once. Should we use args->size() instead?
OK, no problem. Done.
>> + std::vector<struct dtrace_probe_arg> m_args;
>>
>> /* A probe can have zero or more "enablers" associated with it. */
>> - VEC (dtrace_probe_enabler_s) *enablers;
>> + std::vector<struct dtrace_probe_enabler> m_enablers;
>>
>> /* Whether the expressions for the arguments have been built. */
>> - unsigned int args_expr_built : 1;
>> + bool m_args_expr_built;
>> };
>>
>> -/* Implementation of the probe_is_linespec method. */
>> -
>> -static int
>> -dtrace_probe_is_linespec (const char **linespecp)
>> -{
>> - static const char *const keywords[] = { "-pdtrace", "-probe-dtrace", NULL };
>> -
>> - return probe_is_linespec_by_keyword (linespecp, keywords);
>> -}
>> -
>> /* DOF programs can contain an arbitrary number of sections of 26
>> different types. In order to support DTrace USDT probes we only
>> need to handle a subset of these section types, fortunately. These
>> @@ -322,8 +397,6 @@ dtrace_process_dof_probe (struct objfile *objfile,
>> char *argtab, uint64_t strtab_size)
>> {
>> int i, j, num_probes, num_enablers;
>> - struct cleanup *cleanup;
>> - VEC (dtrace_probe_enabler_s) *enablers;
>> char *p;
>>
>> /* Each probe section can define zero or more probes of two
>> @@ -368,9 +441,7 @@ dtrace_process_dof_probe (struct objfile *objfile,
>>
>> /* Build the list of enablers for the probes defined in this Probe
>> DOF section. */
>> - enablers = NULL;
>> - cleanup
>> - = make_cleanup (VEC_cleanup (dtrace_probe_enabler_s), &enablers);
>> + std::vector<struct dtrace_probe_enabler> enablers;
>> num_enablers = DOF_UINT (dof, probe->dofpr_nenoffs);
>> for (i = 0; i < num_enablers; i++)
>> {
>> @@ -380,38 +451,32 @@ dtrace_process_dof_probe (struct objfile *objfile,
>>
>> enabler.address = DOF_UINT (dof, probe->dofpr_addr)
>> + DOF_UINT (dof, enabler_offset);
>> - VEC_safe_push (dtrace_probe_enabler_s, enablers, &enabler);
>> + enablers.push_back (enabler);
>> }
>>
>> for (i = 0; i < num_probes; i++)
>> {
>> uint32_t probe_offset
>> = ((uint32_t *) offtab)[DOF_UINT (dof, probe->dofpr_offidx) + i];
>> - struct dtrace_probe *ret =
>> - XOBNEW (&objfile->per_bfd->storage_obstack, struct dtrace_probe);
>> -
>> - ret->p.pops = &dtrace_probe_ops;
>> - ret->p.arch = gdbarch;
>> - ret->args_expr_built = 0;
>>
>> /* Set the provider and the name of the probe. */
>> - ret->p.provider
>> - = xstrdup (strtab + DOF_UINT (dof, provider->dofpv_name));
>> - ret->p.name = xstrdup (strtab + DOF_UINT (dof, probe->dofpr_name));
>> + const char *probe_provider
>> + = strtab + DOF_UINT (dof, provider->dofpv_name);
>> + const char *name = strtab + DOF_UINT (dof, probe->dofpr_name);
>>
>> /* The probe address. */
>> - ret->p.address
>> + CORE_ADDR address
>> = DOF_UINT (dof, probe->dofpr_addr) + DOF_UINT (dof, probe_offset);
>>
>> /* Number of arguments in the probe. */
>> - ret->probe_argc = DOF_UINT (dof, probe->dofpr_nargc);
>> + int probe_argc = DOF_UINT (dof, probe->dofpr_nargc);
>>
>> /* Store argument type descriptions. A description of the type
>> of the argument is in the (J+1)th null-terminated string
>> starting at 'strtab' + 'probe->dofpr_nargv'. */
>> - ret->args = NULL;
>> + std::vector<struct dtrace_probe_arg> args;
>> p = strtab + DOF_UINT (dof, probe->dofpr_nargv);
>> - for (j = 0; j < ret->probe_argc; j++)
>> + for (j = 0; j < probe_argc; j++)
>> {
>> struct dtrace_probe_arg arg;
>> expression_up expr;
>> @@ -442,17 +507,18 @@ dtrace_process_dof_probe (struct objfile *objfile,
>> if (expr != NULL && expr->elts[0].opcode == OP_TYPE)
>> arg.type = expr->elts[1].type;
>>
>> - VEC_safe_push (dtrace_probe_arg_s, ret->args, &arg);
>> + args.push_back (arg);
>> }
>>
>> - /* Add the vector of enablers to this probe, if any. */
>> - ret->enablers = VEC_copy (dtrace_probe_enabler_s, enablers);
>> + std::vector<struct dtrace_probe_enabler> enablers_copy = enablers;
>
> Why is this copy necessary? What happens with the original vector?
This copy is necessary because the original vector should be intact on
every iteration, but dtrace_probe's constructor performs a 'std::move'
on it. I could have passed the original vector as an argument (by
value), and not perform the std::move in the constructor, if you prefer.
>> + dtrace_probe *ret = new dtrace_probe (std::string (name),
>> + std::string (probe_provider),
>> + address, gdbarch,
>> + args, enablers_copy);
>>
>> /* Successfully created probe. */
>> - probesp->push_back ((struct probe *) ret);
>> + probesp->push_back (ret);
>> }
>> -
>> - do_cleanups (cleanup);
>> }
>>
>> /* Helper function to collect the probes described in the DOF program
>> @@ -555,28 +621,23 @@ dtrace_process_dof (asection *sect, struct objfile *objfile,
>> sect->name);
>> }
>>
>> -/* Helper function to build the GDB internal expressiosn that, once
>> - evaluated, will calculate the values of the arguments of a given
>> - PROBE. */
>> +/* Implementation of 'build_arg_exprs' method. */
>>
>> -static void
>> -dtrace_build_arg_exprs (struct dtrace_probe *probe,
>> - struct gdbarch *gdbarch)
>> +void
>> +dtrace_probe::build_arg_exprs (struct gdbarch *gdbarch)
>> {
>> - struct parser_state pstate;
>> - struct dtrace_probe_arg *arg;
>> - int i;
>> -
>> - probe->args_expr_built = 1;
>> + m_args_expr_built = true;
>>
>> /* Iterate over the arguments in the probe and build the
>> corresponding GDB internal expression that will generate the
>> value of the argument when executed at the PC of the probe. */
>> - for (i = 0; i < probe->probe_argc; i++)
>> + for (int i = 0; i < m_argc; i++)
>> {
>> + struct dtrace_probe_arg *arg;
>> struct cleanup *back_to;
>> + struct parser_state pstate;
>>
>> - arg = VEC_index (dtrace_probe_arg_s, probe->args, i);
>> + arg = &m_args[i];
>>
>> /* Initialize the expression buffer in the parser state. The
>> language does not matter, since we are using our own
>> @@ -606,138 +667,82 @@ dtrace_build_arg_exprs (struct dtrace_probe *probe,
>> }
>> }
>>
>> -/* Helper function to return the Nth argument of a given PROBE. */
>> -
>> -static struct dtrace_probe_arg *
>> -dtrace_get_arg (struct dtrace_probe *probe, unsigned n,
>> - struct gdbarch *gdbarch)
>> -{
>> - if (!probe->args_expr_built)
>> - dtrace_build_arg_exprs (probe, gdbarch);
>> -
>> - return VEC_index (dtrace_probe_arg_s, probe->args, n);
>> -}
>> -
>> -/* Implementation of the get_probes method. */
>> +/* Implementation of 'get_arg_by_number' method. */
>>
>> -static void
>> -dtrace_get_probes (std::vector<probe *> *probesp, struct objfile *objfile)
>> +struct dtrace_probe_arg *
>> +dtrace_probe::get_arg_by_number (unsigned n, struct gdbarch *gdbarch)
>> {
>> - bfd *abfd = objfile->obfd;
>> - asection *sect = NULL;
>> -
>> - /* Do nothing in case this is a .debug file, instead of the objfile
>> - itself. */
>> - if (objfile->separate_debug_objfile_backlink != NULL)
>> - return;
>> + if (!m_args_expr_built)
>> + this->build_arg_exprs (gdbarch);
>>
>> - /* Iterate over the sections in OBJFILE looking for DTrace
>> - information. */
>> - for (sect = abfd->sections; sect != NULL; sect = sect->next)
>> - {
>> - if (elf_section_data (sect)->this_hdr.sh_type == SHT_SUNW_dof)
>> - {
>> - bfd_byte *dof;
>> -
>> - /* Read the contents of the DOF section and then process it to
>> - extract the information of any probe defined into it. */
>> - if (!bfd_malloc_and_get_section (abfd, sect, &dof))
>> - complaint (&symfile_complaints,
>> - _("could not obtain the contents of"
>> - "section '%s' in objfile `%s'."),
>> - sect->name, abfd->filename);
>> -
>> - dtrace_process_dof (sect, objfile, probesp,
>> - (struct dtrace_dof_hdr *) dof);
>> - xfree (dof);
>> - }
>> - }
>> + return &m_args[n];
>
> It would be nice to add a gdb_assert (n < m_args.size ()) here.
I've added a bound check and an internal_error, just like I did for
stap-probe.
Thanks,
--
Sergio
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