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Add LoongArch support for kpatch v2 #1427

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2e0551d
kpatch/LoongArch: Add LoongArch specific features
georgejguo Aug 8, 2024
4835b29
kpatch/LoongArch: Add initial support for kpatch
georgejguo Aug 17, 2024
daf9377
kpatch/LoongArch: process section __patchable_function_entries
georgejguo Dec 5, 2024
a33aec9
kpatch/LoongArch: change local labels with sections symbols
georgejguo Dec 5, 2024
018676a
kpatch/LoongArch: skip section .rela.orc_unwind_ip
georgejguo Dec 11, 2024
c568de1
kpatch/LoongArch: enable kpatch build
georgejguo Nov 7, 2024
850331f
kpatch/LoongArch: fix build error on non-LoongArch architectures
georgejguo Nov 8, 2024
eab48a0
kpatch/LoongArch: ignore arch/loongarch/vdso
georgejguo Jan 22, 2025
57d1458
kpatch/LoongArch: disable direct-extern-access for livepatches to fix…
georgejguo Sep 22, 2025
3d44f1b
kpatch/LoongArch: fix kernel panic with -fPIC for same-compilation-un…
Nov 17, 2025
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2 changes: 1 addition & 1 deletion kpatch-build/Makefile
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Expand Up @@ -21,7 +21,7 @@ PLUGIN_CFLAGS := $(filter-out -std=gnu11 -Wconversion, $(CFLAGS))
PLUGIN_CFLAGS += -shared -I$(GCC_PLUGINS_DIR)/include \
-Igcc-plugins -fPIC -fno-rtti -O2 -Wall
endif
ifeq ($(filter $(ARCH),s390x x86_64 ppc64le aarch64),)
ifeq ($(filter $(ARCH),s390x x86_64 ppc64le aarch64 loongarch64),)
$(error Unsupported architecture ${ARCH}, check https://github.com/dynup/kpatch/#supported-architectures)
endif

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44 changes: 39 additions & 5 deletions kpatch-build/create-diff-object.c
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Expand Up @@ -182,6 +182,8 @@ static bool is_gcc6_localentry_bundled_sym(struct kpatch_elf *kelf,
return false;
case S390:
return false;
case LOONGARCH64:
return false;
default:
ERROR("unsupported arch");
}
Expand Down Expand Up @@ -247,6 +249,7 @@ static bool kpatch_is_mapping_symbol(struct kpatch_elf *kelf, struct symbol *sym
case X86_64:
case PPC64:
case S390:
case LOONGARCH64:
return false;
default:
ERROR("unsupported arch");
Expand Down Expand Up @@ -762,6 +765,11 @@ static bool insn_is_load_immediate(struct kpatch_elf *kelf, void *addr)

break;

case LOONGARCH64:
/* to be done */
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@joe-lawrence joe-lawrence Dec 5, 2024

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TODO?

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@georgejguo georgejguo Dec 6, 2024

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I m not sure here, so just commit "to be done". Actually it can pass my simple test case.

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@joe-lawrence joe-lawrence Dec 23, 2025

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This function is used to detect when a section has changed only due to __LINE__ macro changes (e.g., in WARN() or might_sleep() calls). The current implementation will return false for LoongArch64, which means it won't detect __LINE__-only changes. This is acceptable as a temporary measure (the function will still work, just won't optimize away false positives), but shouldn't be hard to implement.

I don't have a loongarch64 kernel handy, but with clang I see something like:

$ diff -upr a.asm b.asm
--- a.asm       2025-12-23 12:28:07.114272945 -0500
+++ b.asm       2025-12-23 12:27:27.656155418 -0500
@@ -9,7 +9,7 @@ Disassembly of section .text:
    4:  29c06061        st.d            $ra, $sp, 24
    8:  29c04076        st.d            $fp, $sp, 16
    c:  02c08076        addi.d          $fp, $sp, 32
-  10:  03800804        li.w            $a0, 0x2
+  10:  03801804        li.w            $a0, 0x6
   14:  29bfb2c4        st.w            $a0, $fp, -20
   18:  28bfb2c4        ld.w            $a0, $fp, -20
   1c:  28c04076        ld.d            $fp, $sp, 16

when I shift around the source lines of:

int fun(void) {
    int a = __LINE__;
    return a;
}

I would try editing a file like kernel/fork.c and add something like pr_info("%d", __LINE__); to nr_processes() and a simple pr_info("kpatch"); to copy_signal(). Then create a kpatch that moves the first change down a few lines in the source file and update the "kpatch" string. Ideally kpatch-build will only pull out the changes to copy_signal() and ignore the trivial debugging line number update in nr_processes().

To handle this on loongarch64, hopefully it's as simple as adding the li.w opcodes here (like the other arches). I'd be willing to merge w/o if you want to do this as a follow up, but thought I'd at least explain it here, let me know.


break;

case S390:
/* arg2: lghi %r3, imm */
if (insn[0] == 0xa7 && insn[1] == 0x39)
Expand Down Expand Up @@ -2589,22 +2597,22 @@ static bool static_call_sites_group_filter(struct lookup_table *lookup,
static struct special_section special_sections[] = {
{
.name = "__bug_table",
.arch = AARCH64 | X86_64 | PPC64 | S390,
.arch = AARCH64 | X86_64 | PPC64 | S390 | LOONGARCH64,
.group_size = bug_table_group_size,
},
{
.name = ".fixup",
.arch = AARCH64 | X86_64 | PPC64 | S390,
.arch = AARCH64 | X86_64 | PPC64 | S390 | LOONGARCH64,
.group_size = fixup_group_size,
},
{
.name = "__ex_table", /* must come after .fixup */
.arch = AARCH64 | X86_64 | PPC64 | S390,
.arch = AARCH64 | X86_64 | PPC64 | S390 | LOONGARCH64,
.group_size = ex_table_group_size,
},
{
.name = "__jump_table",
.arch = AARCH64 | X86_64 | PPC64 | S390,
.arch = AARCH64 | X86_64 | PPC64 | S390 | LOONGARCH64,
.group_size = jump_table_group_size,
.group_filter = jump_table_group_filter,
},
Expand All @@ -2625,7 +2633,7 @@ static struct special_section special_sections[] = {
},
{
.name = ".altinstructions",
.arch = AARCH64 | X86_64 | S390,
.arch = AARCH64 | X86_64 | S390 | LOONGARCH64,
.group_size = altinstructions_group_size,
},
{
Expand Down Expand Up @@ -3048,6 +3056,11 @@ static void kpatch_mark_ignored_sections(struct kpatch_elf *kelf)
!strcmp(sec->name, "__patchable_function_entries"))
sec->ignore = 1;
}

if (kelf->arch == LOONGARCH64) {
if(!strncmp(sec->name,".rela.orc_unwind_ip",19))
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@joe-lawrence joe-lawrence Dec 23, 2025

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nit: spacing, should be; if (!strncmp(sec->name,".rela.orc_unwind_ip", 19))

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@joe-lawrence joe-lawrence Dec 23, 2025

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Also, any idea why .rela.orc_unwind_ip is needed only on LoongArch64? What about .rela.orc_unwind ?

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@georgejguo georgejguo Dec 25, 2025

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done

sec->ignore = 1;
}
}

sec = find_section_by_name(&kelf->sections, ".kpatch.ignore.sections");
Expand Down Expand Up @@ -4050,6 +4063,21 @@ static void kpatch_create_ftrace_callsite_sections(struct kpatch_elf *kelf)
insn_offset = sym->sym.st_value;
break;
}
case LOONGARCH64: {
bool found = false;
unsigned char *insn = sym->sec->data->d_buf + sym->sym.st_value;

/* 0x03400000 is NOP instruction for LoongArch. */
if(insn[0] == 0x00 && insn[1] == 0x00 && insn[2] == 0x40 && insn[3] == 0x03 &&
insn[4] == 0x00 && insn[5] == 0x00 && insn[6] == 0x40 && insn[7] == 0x03)
found = true;

if (!found)
ERROR("%s: unexpected instruction at the start of the function", sym->name);

insn_offset = 0;
break;
}
default:
ERROR("unsupported arch");
}
Expand Down Expand Up @@ -4311,6 +4339,12 @@ static void kpatch_find_func_profiling_calls(struct kpatch_elf *kelf)
if (kpatch_symbol_has_pfe_entry(kelf, sym))
sym->has_func_profiling = 1;
break;
case LOONGARCH64:

if (kpatch_symbol_has_pfe_entry(kelf, sym))
sym->has_func_profiling = 1;
break;

default:
ERROR("unsupported arch");
}
Expand Down
31 changes: 31 additions & 0 deletions kpatch-build/kpatch-build
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Expand Up @@ -61,6 +61,7 @@ KLP_REPLACE=1

GCC="${CROSS_COMPILE:-}gcc"
CLANG="${CROSS_COMPILE:-}clang"
CC_OPTION=""
LD="${CROSS_COMPILE:-}ld"
LLD="${CROSS_COMPILE:-}ld.lld"
READELF="${CROSS_COMPILE:-}readelf"
Expand Down Expand Up @@ -382,6 +383,21 @@ clang_version_check() {
return
}

cc_option_check() {
local option="$1"
local compiler=""

if [[ -n "$CONFIG_CC_IS_CLANG" ]]; then
compiler="$CLANG"
else
compiler="$GCC"
fi

if $compiler -Werror "$option" -c -x c /dev/null -o /dev/null 2>/dev/null; then
CC_OPTION+=" $option";
fi
}

find_special_section_data() {
local -A check

Expand All @@ -405,6 +421,9 @@ find_special_section_data() {
"aarch64")
check[a]=true # alt_instr
;;
"loongarch64")
check[a]=true # alt_instr
;;
esac

# Kernel CONFIG_ features
Expand Down Expand Up @@ -1269,6 +1288,10 @@ if [[ "$ARCH" = "s390x" ]]; then
! kernel_version_gte 6.10.0 && ARCH_KCFLAGS+=" -fPIE"
fi

if [[ "$ARCH" = "loongarch64" ]]; then
ARCH_KCFLAGS="-fPIC"
fi

export KCFLAGS="-I$DATADIR/patch -ffunction-sections -fdata-sections \
$ARCH_KCFLAGS $DEBUG_KCFLAGS"

Expand All @@ -1288,7 +1311,15 @@ declare -a MAKEVARS
if [[ -n "$CONFIG_CC_IS_CLANG" ]]; then
MAKEVARS+=("CC=${KPATCH_CC_PREFIX}${CLANG}")
MAKEVARS+=("HOSTCC=clang")
if [[ "$ARCH" = "loongarch64" ]]; then
cc_option_check "-fno-direct-access-external-data"
MAKEVARS+=("KBUILD_CFLAGS_KERNEL+=${CC_OPTION}")
fi
else
if [[ "$ARCH" = "loongarch64" ]]; then
cc_option_check "-mno-direct-extern-access"
MAKEVARS+=("KBUILD_CFLAGS_KERNEL+=${CC_OPTION}")
fi
MAKEVARS+=("CC=${KPATCH_CC_PREFIX}${GCC}")
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@joe-lawrence joe-lawrence Dec 23, 2025

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Nit: just a consistency nit here, can we set the arch MAKEVARS after the existing (non-arch) ones in both clang/gcc cases?

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@georgejguo georgejguo Dec 25, 2025 •
edited
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Nit: just a consistency nit here, can we set the arch MAKEVARS after the existing (non-arch) ones in both clang/gcc cases?

It sounds like this:

if [[ -n "$CONFIG_CC_IS_CLANG" ]]; then
        MAKEVARS+=("CC=${KPATCH_CC_PREFIX}${CLANG}")
        MAKEVARS+=("HOSTCC=clang")
+       if [[ "$ARCH" = "loongarch64" ]]; then
+               cc_option_check "-fno-direct-access-external-data"
+               MAKEVARS+=("KBUILD_CFLAGS_KERNEL+=${CC_OPTION}")
+       fi
 else
        MAKEVARS+=("CC=${KPATCH_CC_PREFIX}${GCC}")
+       if [[ "$ARCH" = "loongarch64" ]]; then
+               cc_option_check "-mno-direct-extern-access"
+               MAKEVARS+=("KBUILD_CFLAGS_KERNEL+=${CC_OPTION}")
+       fi
 fi

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@georgejguo georgejguo Dec 25, 2025

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done

fi

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1 change: 1 addition & 0 deletions kpatch-build/kpatch-cc
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Expand Up @@ -43,6 +43,7 @@ if [[ "$TOOLCHAINCMD" =~ ^(.*-)?gcc$ || "$TOOLCHAINCMD" =~ ^(.*-)?clang$ ]] ; th
arch/s390/boot/*|\
arch/s390/purgatory/*|\
arch/s390/kernel/vdso64/*|\
arch/loongarch/vdso/*|\
drivers/firmware/efi/libstub/*|\
init/version.o|\
init/version-timestamp.o|\
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35 changes: 35 additions & 0 deletions kpatch-build/kpatch-elf.c
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Expand Up @@ -156,6 +156,8 @@ unsigned int absolute_rela_type(struct kpatch_elf *kelf)
return R_390_64;
case AARCH64:
return R_AARCH64_ABS64;
case LOONGARCH64:
return R_LARCH_64;
default:
ERROR("unsupported arch");
}
Expand Down Expand Up @@ -221,6 +223,7 @@ long rela_target_offset(struct kpatch_elf *kelf, struct section *relasec,
switch(kelf->arch) {
case PPC64:
case AARCH64:
case LOONGARCH64:
add_off = 0;
break;
case X86_64:
Expand Down Expand Up @@ -278,6 +281,7 @@ unsigned int insn_length(struct kpatch_elf *kelf, void *addr)
return decoded_insn.length;

case PPC64:
case LOONGARCH64:
return 4;

case S390:
Expand Down Expand Up @@ -349,6 +353,22 @@ static void kpatch_create_rela_list(struct kpatch_elf *kelf,
rela->sym->name, rela->addend);
}

if (kelf->arch == LOONGARCH64) {
/*
* LoongArch GCC creates local labels such as .LBB7266,
* replace them with section symbols.
*/
if (rela->sym->sec && (rela->sym->type == STT_NOTYPE) &&
(rela->sym->bind == STB_LOCAL)) {
log_debug("local label: %s -> ", rela->sym->name);

rela->addend += rela->sym->sym.st_value;
rela->sym = rela->sym->sec->secsym;
log_debug("section symbol: %s\n", rela->sym->name);
}
}
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@joe-lawrence joe-lawrence Dec 5, 2024

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Just curious, which kernel source files are generating these symbols?

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@georgejguo georgejguo Dec 6, 2024

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Okey, I will try to find it.

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@joe-lawrence joe-lawrence Dec 23, 2025

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Nit: extra blank line here



if (skip)
continue;
log_debug("offset %d, type %d, %s %s %ld", rela->offset,
Expand Down Expand Up @@ -614,6 +634,9 @@ struct kpatch_elf *kpatch_elf_open(const char *name)
case EM_AARCH64:
kelf->arch = AARCH64;
break;
case EM_LOONGARCH:
kelf->arch = LOONGARCH64;
break;
default:
ERROR("Unsupported target architecture");
}
Expand Down Expand Up @@ -647,6 +670,18 @@ struct kpatch_elf *kpatch_elf_open(const char *name)
}
}

if (kelf->arch == LOONGARCH64) {
struct symbol *sym, *tmp;

/* Delete local labels created by LoongArch GCC */
list_for_each_entry_safe(sym, tmp, &kelf->symbols, list) {
if (sym->sec && !is_rela_section(sym->sec) &&
(sym->type == STT_NOTYPE) &&
(sym->bind == STB_LOCAL))
list_del(&sym->list);
}
}

return kelf;
}

Expand Down
6 changes: 6 additions & 0 deletions kpatch-build/kpatch-elf.h
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Expand Up @@ -31,6 +31,11 @@
#define SHF_RELA_LIVEPATCH 0x00100000
#define SHN_LIVEPATCH 0xff20

#ifndef __loongarch__
#define EM_LOONGARCH 258 /* LoongArch */
#define R_LARCH_64 2
#endif

/*******************
* Data structures
* ****************/
Expand Down Expand Up @@ -117,6 +122,7 @@ enum architecture {
X86_64 = 0x1 << 1,
S390 = 0x1 << 2,
AARCH64 = 0x1 << 3,
LOONGARCH64 = 0x1 << 4,
};

struct kpatch_elf {
Expand Down