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Subject[PATCH 2/2] vmlinux.lds.h: add HEADERED_SECTION_* macros
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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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