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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> |
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| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.