Messages in this thread Patch in this message | | | From | Jim Cromie <> | Subject | [PATCH 2/2] vmlinux.lds.h: add HEADERED_SECTION_* macros | Date | Wed, 16 Nov 2022 17:20:22 -0700 |
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These macros elaborate on BOUNDED_SECTION_(PRE|POST)_LABEL macros, prepending an optional KEEP(.gnu.linkonce##_sec_) reservation, and a linker-symbol to address it.
This allows a developer to define a header struct (which must fit with the section's base struct-type), and could contain:
1- fields whose value is common to the entire set of data-records. This allows the header & data structs to specialize, complement each other, and shrink.
2- an uplink pointer to an organizing struct which refs other related/sub data-tables header record is addressable via the extern'd header linker-symbol
Once the linker-symbols created by the macro are ref'd extern in code, that code can compute a record's index (ptr - start) in the "primary" table, then use it to index into the related/sub tables. Adding a primary.map_* field foreach sub-table would then allow deduplication and remapping of that sub-table.
This is aimed at dyndbg's struct _ddebug __dyndbg[] section, whose 3 columns: function, file, module are 50%, 90%, 100% redundant. The module column is fully recoverable after dynamic_debug_init() saves it to each ddebug_table.module as the builtin __dyndbg[] table is parsed.
Given that those 3 columns use 24/56 of a prdbg record, a dyndbg=y kernel with ~5k callsites could save substantially.
Signed-off-by: Jim Cromie <jim.cromie@gmail.com> --- --- include/asm-generic/vmlinux.lds.h | 15 +++++++++++++++ 1 file changed, 15 insertions(+)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 85d5d5b203dc..a3b6aa30a525 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -214,6 +214,21 @@ #define BOUNDED_SECTION(_sec) BOUNDED_SECTION_BY(_sec, _sec) +#define HEADERED_SECTION_PRE_LABEL(_sec_, _label_, _BEGIN_, _END_, _HDR_) \ + _HDR_##_label_ = .; \ + KEEP(*(.gnu.linkonce.##_sec_)) \ + BOUNDED_SECTION_PRE_LABEL(_sec_, _label_, _BEGIN_, _END_) + +#define HEADERED_SECTION_POST_LABEL(_sec_, _label_, _BEGIN_, _END_, _HDR_) \ + _label_##_HDR_ = .; \ + KEEP(*(.gnu.linkonce.##_sec_)) \ + BOUNDED_SECTION_POST_LABEL(_sec_, _label_, _BEGIN_, _END_) + +#define HEADERED_SECTION_BY(_sec_, _label_) \ + HEADERED_SECTION_PRE_LABEL(_sec_, _label_, __start, __stop) + +#define HEADERED_SECTION(_sec) HEADERED_SECTION_BY(_sec, _sec) + #ifdef CONFIG_TRACE_BRANCH_PROFILING #define LIKELY_PROFILE() \ BOUNDED_SECTION_BY(_ftrace_annotated_branch, _annotated_branch_profile) -- 2.38.1
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