[28/48] perf dwarf-aux: Add die_find_variable_by_addr()
Commit Message
The die_find_variable_by_addr() is to find a variables in the given DIE
using given (PC-relative) address. Global variables will have a
location expression with DW_OP_addr which has an address so can simply
compare it with the address.
<1><143a7>: Abbrev Number: 2 (DW_TAG_variable)
<143a8> DW_AT_name : loops_per_jiffy
<143ac> DW_AT_type : <0x1cca>
<143b0> DW_AT_external : 1
<143b0> DW_AT_decl_file : 193
<143b1> DW_AT_decl_line : 213
<143b2> DW_AT_location : 9 byte block: 3 b0 46 41 82 ff ff ff ff
(DW_OP_addr: ffffffff824146b0)
Note that the type-offset should be calculated from the base address of
the global variable.
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
tools/perf/util/dwarf-aux.c | 80 +++++++++++++++++++++++++++++++++++++
tools/perf/util/dwarf-aux.h | 14 +++++++
2 files changed, 94 insertions(+)
Comments
On Wed, 11 Oct 2023 20:50:51 -0700
Namhyung Kim <namhyung@kernel.org> wrote:
> The die_find_variable_by_addr() is to find a variables in the given DIE
> using given (PC-relative) address. Global variables will have a
> location expression with DW_OP_addr which has an address so can simply
> compare it with the address.
>
> <1><143a7>: Abbrev Number: 2 (DW_TAG_variable)
> <143a8> DW_AT_name : loops_per_jiffy
> <143ac> DW_AT_type : <0x1cca>
> <143b0> DW_AT_external : 1
> <143b0> DW_AT_decl_file : 193
> <143b1> DW_AT_decl_line : 213
> <143b2> DW_AT_location : 9 byte block: 3 b0 46 41 82 ff ff ff ff
> (DW_OP_addr: ffffffff824146b0)
>
> Note that the type-offset should be calculated from the base address of
> the global variable.
>
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Looks good to me.
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
BTW, for the global variable, you can also find it via maps. Can't you?
Thanks,
> ---
> tools/perf/util/dwarf-aux.c | 80 +++++++++++++++++++++++++++++++++++++
> tools/perf/util/dwarf-aux.h | 14 +++++++
> 2 files changed, 94 insertions(+)
>
> diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
> index 5bb05c84d249..97d9ae56350e 100644
> --- a/tools/perf/util/dwarf-aux.c
> +++ b/tools/perf/util/dwarf-aux.c
> @@ -1266,8 +1266,12 @@ int die_get_var_range(Dwarf_Die *sp_die, Dwarf_Die *vr_die, struct strbuf *buf)
> struct find_var_data {
> /* Target instruction address */
> Dwarf_Addr pc;
> + /* Target memory address (for global data) */
> + Dwarf_Addr addr;
> /* Target register */
> unsigned reg;
> + /* Access offset, set for global data */
> + int offset;
> };
>
> /* Max number of registers DW_OP_regN supports */
> @@ -1328,6 +1332,82 @@ Dwarf_Die *die_find_variable_by_reg(Dwarf_Die *sc_die, Dwarf_Addr pc, int reg,
> };
> return die_find_child(sc_die, __die_find_var_reg_cb, &data, die_mem);
> }
> +
> +/* Only checks direct child DIEs in the given scope */
> +static int __die_find_var_addr_cb(Dwarf_Die *die_mem, void *arg)
> +{
> + struct find_var_data *data = arg;
> + int tag = dwarf_tag(die_mem);
> + ptrdiff_t off = 0;
> + Dwarf_Attribute attr;
> + Dwarf_Addr base, start, end;
> + Dwarf_Word size;
> + Dwarf_Die type_die;
> + Dwarf_Op *ops;
> + size_t nops;
> +
> + if (tag != DW_TAG_variable)
> + return DIE_FIND_CB_SIBLING;
> +
> + if (dwarf_attr(die_mem, DW_AT_location, &attr) == NULL)
> + return DIE_FIND_CB_SIBLING;
> +
> + while ((off = dwarf_getlocations(&attr, off, &base, &start, &end, &ops, &nops)) > 0) {
> + if (ops->atom != DW_OP_addr)
> + continue;
> +
> + if (data->addr < ops->number)
> + continue;
> +
> + if (data->addr == ops->number) {
> + /* Update offset relative to the start of the variable */
> + data->offset = 0;
> + return DIE_FIND_CB_END;
> + }
> +
> + if (die_get_real_type(die_mem, &type_die) == NULL)
> + continue;
> +
> + if (dwarf_aggregate_size(&type_die, &size) < 0)
> + continue;
> +
> + if (data->addr >= ops->number + size)
> + continue;
> +
> + /* Update offset relative to the start of the variable */
> + data->offset = data->addr - ops->number;
> + return DIE_FIND_CB_END;
> + }
> + return DIE_FIND_CB_SIBLING;
> +}
> +
> +/**
> + * die_find_variable_by_addr - Find variable located at given address
> + * @sc_die: a scope DIE
> + * @pc: the program address to find
> + * @addr: the data address to find
> + * @die_mem: a buffer to save the resulting DIE
> + * @offset: the offset in the resulting type
> + *
> + * Find the variable DIE located at the given address (in PC-relative mode).
> + * This is usually for global variables.
> + */
> +Dwarf_Die *die_find_variable_by_addr(Dwarf_Die *sc_die, Dwarf_Addr pc,
> + Dwarf_Addr addr, Dwarf_Die *die_mem,
> + int *offset)
> +{
> + struct find_var_data data = {
> + .pc = pc,
> + .addr = addr,
> + };
> + Dwarf_Die *result;
> +
> + result = die_find_child(sc_die, __die_find_var_addr_cb, &data, die_mem);
> + if (result)
> + *offset = data.offset;
> + return result;
> +}
> +
> #endif
>
> /*
> diff --git a/tools/perf/util/dwarf-aux.h b/tools/perf/util/dwarf-aux.h
> index 574405c57d3b..742098e3ee7e 100644
> --- a/tools/perf/util/dwarf-aux.h
> +++ b/tools/perf/util/dwarf-aux.h
> @@ -144,6 +144,11 @@ int die_get_var_range(Dwarf_Die *sp_die, Dwarf_Die *vr_die, struct strbuf *buf);
> Dwarf_Die *die_find_variable_by_reg(Dwarf_Die *sc_die, Dwarf_Addr pc, int reg,
> Dwarf_Die *die_mem);
>
> +/* Find a (global) variable located in the 'addr' */
> +Dwarf_Die *die_find_variable_by_addr(Dwarf_Die *sc_die, Dwarf_Addr pc,
> + Dwarf_Addr addr, Dwarf_Die *die_mem,
> + int *offset);
> +
> #else /* HAVE_DWARF_GETLOCATIONS_SUPPORT */
>
> static inline int die_get_var_range(Dwarf_Die *sp_die __maybe_unused,
> @@ -161,6 +166,15 @@ static inline Dwarf_Die *die_find_variable_by_reg(Dwarf_Die *sc_die __maybe_unus
> return NULL;
> }
>
> +static inline Dwarf_Die *die_find_variable_by_addr(Dwarf_Die *sc_die __maybe_unused,
> + Dwarf_Addr pc __maybe_unused,
> + Dwarf_Addr addr __maybe_unused,
> + Dwarf_Die *die_mem __maybe_unused,
> + int *offset __maybe_unused)
> +{
> + return NULL;
> +}
> +
> #endif /* HAVE_DWARF_GETLOCATIONS_SUPPORT */
>
> #endif /* _DWARF_AUX_H */
> --
> 2.42.0.655.g421f12c284-goog
>
>
On Mon, Nov 6, 2023 at 7:25 AM Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> On Wed, 11 Oct 2023 20:50:51 -0700
> Namhyung Kim <namhyung@kernel.org> wrote:
>
> > The die_find_variable_by_addr() is to find a variables in the given DIE
> > using given (PC-relative) address. Global variables will have a
> > location expression with DW_OP_addr which has an address so can simply
> > compare it with the address.
> >
> > <1><143a7>: Abbrev Number: 2 (DW_TAG_variable)
> > <143a8> DW_AT_name : loops_per_jiffy
> > <143ac> DW_AT_type : <0x1cca>
> > <143b0> DW_AT_external : 1
> > <143b0> DW_AT_decl_file : 193
> > <143b1> DW_AT_decl_line : 213
> > <143b2> DW_AT_location : 9 byte block: 3 b0 46 41 82 ff ff ff ff
> > (DW_OP_addr: ffffffff824146b0)
> >
> > Note that the type-offset should be calculated from the base address of
> > the global variable.
> >
> > Signed-off-by: Namhyung Kim <namhyung@kernel.org>
>
> Looks good to me.
>
> Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
>
> BTW, for the global variable, you can also find it via maps. Can't you?
What do you mean by 'via maps'? The map in perf?
Thanks,
Namhyung
@@ -1266,8 +1266,12 @@ int die_get_var_range(Dwarf_Die *sp_die, Dwarf_Die *vr_die, struct strbuf *buf)
struct find_var_data {
/* Target instruction address */
Dwarf_Addr pc;
+ /* Target memory address (for global data) */
+ Dwarf_Addr addr;
/* Target register */
unsigned reg;
+ /* Access offset, set for global data */
+ int offset;
};
/* Max number of registers DW_OP_regN supports */
@@ -1328,6 +1332,82 @@ Dwarf_Die *die_find_variable_by_reg(Dwarf_Die *sc_die, Dwarf_Addr pc, int reg,
};
return die_find_child(sc_die, __die_find_var_reg_cb, &data, die_mem);
}
+
+/* Only checks direct child DIEs in the given scope */
+static int __die_find_var_addr_cb(Dwarf_Die *die_mem, void *arg)
+{
+ struct find_var_data *data = arg;
+ int tag = dwarf_tag(die_mem);
+ ptrdiff_t off = 0;
+ Dwarf_Attribute attr;
+ Dwarf_Addr base, start, end;
+ Dwarf_Word size;
+ Dwarf_Die type_die;
+ Dwarf_Op *ops;
+ size_t nops;
+
+ if (tag != DW_TAG_variable)
+ return DIE_FIND_CB_SIBLING;
+
+ if (dwarf_attr(die_mem, DW_AT_location, &attr) == NULL)
+ return DIE_FIND_CB_SIBLING;
+
+ while ((off = dwarf_getlocations(&attr, off, &base, &start, &end, &ops, &nops)) > 0) {
+ if (ops->atom != DW_OP_addr)
+ continue;
+
+ if (data->addr < ops->number)
+ continue;
+
+ if (data->addr == ops->number) {
+ /* Update offset relative to the start of the variable */
+ data->offset = 0;
+ return DIE_FIND_CB_END;
+ }
+
+ if (die_get_real_type(die_mem, &type_die) == NULL)
+ continue;
+
+ if (dwarf_aggregate_size(&type_die, &size) < 0)
+ continue;
+
+ if (data->addr >= ops->number + size)
+ continue;
+
+ /* Update offset relative to the start of the variable */
+ data->offset = data->addr - ops->number;
+ return DIE_FIND_CB_END;
+ }
+ return DIE_FIND_CB_SIBLING;
+}
+
+/**
+ * die_find_variable_by_addr - Find variable located at given address
+ * @sc_die: a scope DIE
+ * @pc: the program address to find
+ * @addr: the data address to find
+ * @die_mem: a buffer to save the resulting DIE
+ * @offset: the offset in the resulting type
+ *
+ * Find the variable DIE located at the given address (in PC-relative mode).
+ * This is usually for global variables.
+ */
+Dwarf_Die *die_find_variable_by_addr(Dwarf_Die *sc_die, Dwarf_Addr pc,
+ Dwarf_Addr addr, Dwarf_Die *die_mem,
+ int *offset)
+{
+ struct find_var_data data = {
+ .pc = pc,
+ .addr = addr,
+ };
+ Dwarf_Die *result;
+
+ result = die_find_child(sc_die, __die_find_var_addr_cb, &data, die_mem);
+ if (result)
+ *offset = data.offset;
+ return result;
+}
+
#endif
/*
@@ -144,6 +144,11 @@ int die_get_var_range(Dwarf_Die *sp_die, Dwarf_Die *vr_die, struct strbuf *buf);
Dwarf_Die *die_find_variable_by_reg(Dwarf_Die *sc_die, Dwarf_Addr pc, int reg,
Dwarf_Die *die_mem);
+/* Find a (global) variable located in the 'addr' */
+Dwarf_Die *die_find_variable_by_addr(Dwarf_Die *sc_die, Dwarf_Addr pc,
+ Dwarf_Addr addr, Dwarf_Die *die_mem,
+ int *offset);
+
#else /* HAVE_DWARF_GETLOCATIONS_SUPPORT */
static inline int die_get_var_range(Dwarf_Die *sp_die __maybe_unused,
@@ -161,6 +166,15 @@ static inline Dwarf_Die *die_find_variable_by_reg(Dwarf_Die *sc_die __maybe_unus
return NULL;
}
+static inline Dwarf_Die *die_find_variable_by_addr(Dwarf_Die *sc_die __maybe_unused,
+ Dwarf_Addr pc __maybe_unused,
+ Dwarf_Addr addr __maybe_unused,
+ Dwarf_Die *die_mem __maybe_unused,
+ int *offset __maybe_unused)
+{
+ return NULL;
+}
+
#endif /* HAVE_DWARF_GETLOCATIONS_SUPPORT */
#endif /* _DWARF_AUX_H */