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LoongArch: Add support for relocating the kernel with RELR relocation

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RELR as a relocation packing format for relative relocations for
reducing the size of relative relocation records.  In a position
independent executable there are often many relative relocation
records, and our vmlinux is a PIE.

The LLD linker (since 17.0.0) and the BFD linker (since 2.43) supports
packing the relocations in the RELR format for LoongArch, with the flag
-z pack-relative-relocs.

Commits 5cf896fb6b ("arm64: Add support for relocating the kernel
with RELR relocations") and ccb2d173b9 ("Makefile: use -z
pack-relative-relocs") have already added the framework to use RELR.
We just need to wire it up and process the RELR relocation records in
relocate_relative() in addition to the RELA relocation records.

A ".p2align 3" directive is added to la_abs macro or the BFD linker
cannot pack the relocation records against the .la_abs section (the
". = ALIGN(8);" directive in vmlinux.lds.S is too late in the linking
process).

With defconfig and CONFIG_RELR vmlinux.efi is 2.1 MiB (6%) smaller, and
vmlinuz.efi (using gzip compression) is 384 KiB (2.8%) smaller.

Link: https://groups.google.com/d/topic/generic-abi/bX460iggiKg
Link: https://reviews.llvm.org/D138135#4531389
Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=d89ecf33ab6d
Signed-off-by: Xi Ruoyao <xry111@xry111.site>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
This commit is contained in:
Xi Ruoyao 2024-07-20 22:41:07 +08:00 committed by Huacai Chen
parent 0ad158e4ef
commit e05d4cd9b8
5 changed files with 33 additions and 0 deletions
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1
arch/loongarch/Kconfig
View File

@ -610,6 +610,7 @@ config ARCH_HAS_GENERIC_CRASHKERNEL_RESERVATION
config RELOCATABLE
bool "Relocatable kernel"
select ARCH_HAS_RELR
help
This builds the kernel as a Position Independent Executable (PIE),
which retains all relocation metadata required, so as to relocate

1
arch/loongarch/include/asm/asmmacro.h
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@ -609,6 +609,7 @@
lu32i.d \reg, 0
lu52i.d \reg, \reg, 0
.pushsection ".la_abs", "aw", %progbits
.p2align 3
.dword 766b
.dword \sym
.popsection

5
arch/loongarch/include/asm/setup.h
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@ -34,6 +34,11 @@ extern long __la_abs_end;
extern long __rela_dyn_begin;
extern long __rela_dyn_end;
#ifdef CONFIG_RELR
extern long __relr_dyn_begin;
extern long __relr_dyn_end;
#endif
extern unsigned long __init relocate_kernel(void);
#endif

18
arch/loongarch/kernel/relocate.c
View File

@ -38,6 +38,24 @@ static inline void __init relocate_relative(void)
relocated_addr = (Elf64_Addr)RELOCATED(relocated_addr);
*(Elf64_Addr *)RELOCATED(addr) = relocated_addr;
}
#ifdef CONFIG_RELR
u64 *addr = NULL;
u64 *relr = (u64 *)&__relr_dyn_begin;
u64 *relr_end = (u64 *)&__relr_dyn_end;
for ( ; relr < relr_end; relr++) {
if ((*relr & 1) == 0) {
addr = (u64 *)(*relr + reloc_offset);
*addr++ += reloc_offset;
} else {
for (u64 *p = addr, r = *relr >> 1; r; p++, r >>= 1)
if (r & 1)
*p += reloc_offset;
addr += 63;
}
}
#endif
}
static inline void __init relocate_absolute(long random_offset)

8
arch/loongarch/kernel/vmlinux.lds.S
View File

@ -113,6 +113,14 @@ SECTIONS
__rela_dyn_end = .;
}
#ifdef CONFIG_RELR
.relr.dyn : ALIGN(8) {
__relr_dyn_begin = .;
*(.relr.dyn)
__relr_dyn_end = .;
}
#endif
.data.rel : { *(.data.rel*) }
#ifdef CONFIG_RELOCATABLE