[PATCH 2/4] export.h: make __ksymtab_strings per-symbol section

Masahiro Yamada
2021-02-25T16:06:25Z

The export symbol tables are placed on own sections (__ksymtab*+<sym>)
and sorted by SORT (an alias of SORT_BY_NAME) because the module
subsystem uses the binary search for symbol resolution.

We did not have a good reason to do so for __ksymtab_strings, but
now I have.

To make CONFIG_TRIM_UNUSED_KSYMS work in one-pass, the linker needs
to trim unused strings of symbols and namespaces. To allow per-symbol
keep/drop choice, __ksymtab_strings must be placed on own sections.
Of course, SORT is unneeded here, though.

This keeps the string unification introduced by commit ce2b617ce8cb
("export.h: reduce __ksymtab_strings string duplication by using "MS"
section flags").

For example, the empty namespaces share the same address.

$ nm -n
[ snip ]
ffffffff8233b53a r __kstrtabns_IO_APIC_get_PCI_irq_vector
ffffffff8233b53a r __kstrtabns_I_BDEV
ffffffff8233b53a r __kstrtabns_LZ4_decompress_fast
ffffffff8233b53a r __kstrtabns_LZ4_decompress_fast_continue
ffffffff8233b53a r __kstrtabns_LZ4_decompress_fast_usingDict
ffffffff8233b53a r __kstrtabns_LZ4_decompress_safe
ffffffff8233b53a r __kstrtabns_LZ4_decompress_safe_continue
...

I confirmed no size change in vmlinux.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

include/asm-generic/export.h | 2 +-
include/asm-generic/vmlinux.lds.h | 2 +-
include/linux/export.h | 2 +-
3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/asm-generic/export.h b/include/asm-generic/export.h
index 07a36a874dca..e847f1fde367 100644
--- a/include/asm-generic/export.h
+++ b/include/asm-generic/export.h
@@ -39,7 +39,7 @@
__ksymtab_\name:
__put \val, __kstrtab_\name
.previous
- .section __ksymtab_strings,"aMS",%progbits,1
+ .section __ksymtab_strings+\name,"aMS",%progbits,1
__kstrtab_\name:
.asciz "\name"
.previous
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index c54adce8f6f6..5a2b31890bb8 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -513,7 +513,7 @@
\
/* Kernel symbol table: strings */ \
__ksymtab_strings : AT(ADDR(__ksymtab_strings) - LOAD_OFFSET) { \
- *(__ksymtab_strings) \
+ *(__ksymtab_strings+*) \
} \
\
/* __*init sections */ \
diff --git a/include/linux/export.h b/include/linux/export.h
index 6271a5d9c988..01e6ab19b226 100644
--- a/include/linux/export.h
+++ b/include/linux/export.h
@@ -99,7 +99,7 @@ struct kernel_symbol {
extern const char __kstrtab_##sym[]; \
extern const char __kstrtabns_##sym[]; \
__CRC_SYMBOL(sym, sec); \
- asm(" .section \"__ksymtab_strings\",\"aMS\",%progbits,1 \n" \
+ asm(" .section \"__ksymtab_strings+" #sym "\",\"aMS\",%progbits,1\n" \
"__kstrtab_" #sym ": \n" \
" .asciz \"" #sym "\" \n" \
"__kstrtabns_" #sym ": \n" \
--
2.27.0