RISC-V: Align the .init.text section

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>
Tested-by: Greentime Hu <greentime.hu@sifive.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
index 3ffbd6cbdb8663a8a00650f063c1c15db13e9afb..cacd7898ba7f97562a29c5cd3912d549f0d06e55 100644 (file)
--- 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 = .;