perf dwarf-aux: More accurate variable type match for breg

Introduces the function is_breg_access_indirect to determine whether a
memory access involving a DW_OP_breg* operation refers to the variable's
value directly or requires dereferencing the variable's type as a
pointer based on the DWARF expression.

Previously, all breg based accesses were assumed to directly access the
variable's value (is_pointer = false).

The is_breg_access_indirect function handles three cases:

1. Base register + offset only: (e.g., DW_OP_breg7 RSP+88) The
   calculated address is the location of the variable. The access is
   direct, so no type dereference is needed. Returns false.

2. Base register + offset, followed by other operations ending in
   DW_OP_stack_value, including DW_OP_deref: (e.g., DW_OP_breg*,
   DW_OP_deref, DW_OP_stack_value) The DWARF expression computes the
   variable's value, but that value requires a dereference. The memory
   access is fetching that value, so no type dereference is needed.
   Returns false.

3. Base register + offset, followed only by DW_OP_stack_value: (e.g.,
   DW_OP_breg13 R13+256, DW_OP_stack_value) This indicates the value at
   the base + offset is the variable's value. Since this value is being
   used as an address in the memory access, the variable's type is
   treated as a pointer and requires a type dereference. Returns true.

The is_pointer argument passed to match_var_offset is now set by
is_breg_access_indirect for breg accesses.

There are more complex expressions that includes multiple operations and
may require additional handling, such as DW_OP_deref without a
DW_OP_stack_value, or including multiple base registers. They are less
common in the Linux kernel dwarf and are skipped in check_allowed_ops.

Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Zecheng Li <zecheng@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Xu Liu <xliuprof@google.com>
Link: https://lore.kernel.org/r/CAJUgMyK2wTiEZB__dtgCELmaNGFWhG1j0g9rv_C=cLD6Zq4_5w@mail.gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

0 files changed, 0 insertions, 0 deletions