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FROMGIT: export: Add __gendwarfksyms_ptr_ references to exported symbols

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With gendwarfksyms, we need each TU where the EXPORT_SYMBOL() macro
is used to also contain DWARF type information for the symbols it
exports.  However, as a TU can also export external symbols and
compilers may choose not to emit debugging information for symbols not
defined in the current TU, the missing types will result in missing
symbol versions. Stand-alone assembly code also doesn't contain type
information for exported symbols, so we need to compile a temporary
object file with asm-prototypes.h instead, and similarly need to
ensure the DWARF in the temporary object file contains the necessary
types.

To always emit type information for external exports, add explicit
__gendwarfksyms_ptr_<symbol> references to them in EXPORT_SYMBOL().
gendwarfksyms will use the type information for __gendwarfksyms_ptr_*
if needed. Discard the pointers from the final binary to avoid further
bloat.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
(cherry picked from commit d7476f24c9aa93d02ef3fd8d587a6114387b7667
 https://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git kbuild)
Bug: 347787665
Signed-off-by: Matthew Maurer <mmaurer@google.com>

Change-Id: Iee2f513ee109b7a1d55104b6a6bc47ed260cf26f
Signed-off-by: Matthew Maurer <mmaurer@google.com>
This commit is contained in:
Sami Tolvanen
2025-01-03 20:45:38 +00:00
committed by Giuliano Procida
parent 4a156f73d5
commit bbbb64a40f
1 changed files with 15 additions and 0 deletions
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include/linux/export.h
+15
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@@ -52,9 +52,24 @@
#else
#ifdef CONFIG_GENDWARFKSYMS
/*
* With CONFIG_GENDWARFKSYMS, ensure the compiler emits debugging
* information for all exported symbols, including those defined in
* different TUs, by adding a __gendwarfksyms_ptr_<symbol> pointer
* that's discarded during the final link.
*/
#define __GENDWARFKSYMS_EXPORT(sym) \
static typeof(sym) *__gendwarfksyms_ptr_##sym __used \
__section(".discard.gendwarfksyms") = &sym;
#else
#define __GENDWARFKSYMS_EXPORT(sym)
#endif
#define __EXPORT_SYMBOL(sym, license, ns) \
extern typeof(sym) sym; \
__ADDRESSABLE(sym) \
__GENDWARFKSYMS_EXPORT(sym) \
asm(__stringify(___EXPORT_SYMBOL(sym, license, ns)))
#endif