[PATCH v2 5/8] kconfig: add CONFIG_PUSHSECTION_WITH_RELOC for relocation support

[Yuan Tan]

If the assembler supports the '.reloc' directive with 'BFD_RELOC_NONE', we
can establish a reference between a section created by '.pushsection' and
its caller function by emitting a relocation in the caller.

Known toolchain minimums:
- GNU binutils (gas) >= 2.26
- LLVM integrated assembler (IAS) >= 13.0.0

All assemblers meeting the kernel's minimum toolchain requirements already
support it.

Signed-off-by: Yuan Tan <tanyuan at tinylab.org>
Signed-off-by: Zhangjin Wu <falcon at tinylab.org>
Signed-off-by: Peihan Liu <ronbogo at outlook.com>
---
 init/Kconfig | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/init/Kconfig b/init/Kconfig
index 2c6f86c44d96..3d1cf32d5407 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1631,6 +1631,10 @@ config HAVE_PCSPKR_PLATFORM
 config HAVE_TRIM_UNUSED_SYSCALLS
 	bool
 
+config AS_HAS_BFD_RELOC_NONE
+	bool
+	def_bool $(as-instr,.reloc .$(comma) BFD_RELOC_NONE$(comma))
+
 menuconfig EXPERT
 	bool "Configure standard kernel features (expert users)"
 	# Unhide debug options, to make the on-by-default options visible
@@ -1965,6 +1969,18 @@ config USED_SYSCALLS
 
 	  If unsure, please disable TRIM_UNUSED_SYSCALLS.
 
+config PUSHSECTION_WITH_RELOC
+	bool "Trim more syscalls"
+	depends on TRIM_UNUSED_SYSCALLS && AS_HAS_BFD_RELOC_NONE
+	default y
+	help
+	  Enable building relocation-based references between sections created
+	  by '.pushsection' and their caller functions when the assembler
+	  supports the '.reloc' directive.
+
+	  This allows the linker to establish proper dependencies, remove the
+	  need for KEEP().
+
 config KALLSYMS
 	bool "Load all symbols for debugging/ksymoops" if EXPERT
 	default y
-- 
2.43.0