[PATCH v2 4/6] RISC-V: Align the .init.text section

Atish Patra
2020-10-26T23:03:49Z

In order to improve kernel text protection, we need separate .init.text/
.init.data/.text in separate sections. However, RISC-V linker relaxation
code is not aware of any alignment between sections. As a result, it may
relax any RISCV_CALL relocations between sections to JAL without realizing
that an inter section alignment may move the address farther. That may
lead to a relocation truncated fit error. However, linker relaxation code
is aware of the individual section alignments.

The detailed discussion on this issue can be found here.
https://github.com/riscv/riscv-gnu-toolchain/issues/738

Keep the .init.text section aligned so that linker relaxation will take
that as a hint while relaxing inter section calls.
Here are the code size changes for each section because of this change.

section change in size (in bytes)
.head.text +4
.text +40
.init.text +6530
.exit.text +84

The only significant increase in size happened for .init.text because
all intra relocations also use 2MB alignment.

Suggested-by: Jim Wilson <jimw@sifive.com>
Signed-off-by: Atish Patra <atish.patra@wdc.com>
---
arch/riscv/kernel/vmlinux.lds.S | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
index 3ffbd6cbdb86..cacd7898ba7f 100644
--- a/arch/riscv/kernel/vmlinux.lds.S
+++ b/arch/riscv/kernel/vmlinux.lds.S
@@ -30,7 +30,13 @@ SECTIONS
. = ALIGN(PAGE_SIZE);

__init_begin = .;
- INIT_TEXT_SECTION(PAGE_SIZE)
+ __init_text_begin = .;
+ .init.text : AT(ADDR(.init.text) - LOAD_OFFSET) ALIGN(SECTION_ALIGN) { \
+ _sinittext = .; \
+ INIT_TEXT \
+ _einittext = .; \
+ }
+
. = ALIGN(8);
__soc_early_init_table : {
__soc_early_init_table_start = .;
--
2.25.1