[PATCH v2 11/16] xz: Add ARM64 BCJ filter

Lasse Collin
2024-07-21T13:37:16Z

Also omit a duplicated check for XZ_DEC_ARM in xz_private.h.

A later commit updates lib/decompress_unxz.c to enable this filter for
kernel decompression. lib/decompress_unxz.c is already used if
CONFIG_EFI_ZBOOT=y && CONFIG_KERNEL_XZ=y.

This filter can be used by Squashfs without modifications to the Squashfs
kernel code (only needs support in userspace Squashfs-tools).

Reviewed-by: Sam James <sam@gentoo.org>
Signed-off-by: Lasse Collin <lasse.collin@tukaani.org>
---

Notes:
Compared to the first patch I submitted on 2023-11-08
(<https://lore.kernel.org/lkml/20231108194448.674cd0ad@kaneli/>),
this has a minor tweak to make the for-loop condition faster.

lib/xz/Kconfig | 5 +++++
lib/xz/xz_dec_bcj.c | 52 ++++++++++++++++++++++++++++++++++++++++++++-
lib/xz/xz_private.h | 7 ++++--
3 files changed, 61 insertions(+), 3 deletions(-)

diff --git a/lib/xz/Kconfig b/lib/xz/Kconfig
index 6b80453d8f54..1166627a87dc 100644
--- a/lib/xz/Kconfig
+++ b/lib/xz/Kconfig
@@ -30,6 +30,11 @@ config XZ_DEC_ARMTHUMB
default y
select XZ_DEC_BCJ

+config XZ_DEC_ARM64
+ bool "ARM64 BCJ filter decoder" if EXPERT
+ default y
+ select XZ_DEC_BCJ
+
config XZ_DEC_SPARC
bool "SPARC BCJ filter decoder" if EXPERT
default y
diff --git a/lib/xz/xz_dec_bcj.c b/lib/xz/xz_dec_bcj.c
index e0b4bf4999c0..941198a8a55b 100644
--- a/lib/xz/xz_dec_bcj.c
+++ b/lib/xz/xz_dec_bcj.c
@@ -23,7 +23,8 @@ struct xz_dec_bcj {
BCJ_IA64 = 6, /* Big or little endian */
BCJ_ARM = 7, /* Little endian only */
BCJ_ARMTHUMB = 8, /* Little endian only */
- BCJ_SPARC = 9 /* Big or little endian */
+ BCJ_SPARC = 9, /* Big or little endian */
+ BCJ_ARM64 = 10 /* AArch64 */
} type;

/*
@@ -346,6 +347,47 @@ static size_t bcj_sparc(struct xz_dec_bcj *s, uint8_t *buf, size_t size)
}
#endif

+#ifdef XZ_DEC_ARM64
+static size_t bcj_arm64(struct xz_dec_bcj *s, uint8_t *buf, size_t size)
+{
+ size_t i;
+ uint32_t instr;
+ uint32_t addr;
+
+ size &= ~(size_t)3;
+
+ for (i = 0; i < size; i += 4) {
+ instr = get_unaligned_le32(buf + i);
+
+ if ((instr >> 26) == 0x25) {
+ /* BL instruction */
+ addr = instr - ((s->pos + (uint32_t)i) >> 2);
+ instr = 0x94000000 | (addr & 0x03FFFFFF);
+ put_unaligned_le32(instr, buf + i);
+
+ } else if ((instr & 0x9F000000) == 0x90000000) {
+ /* ADRP instruction */
+ addr = ((instr >> 29) & 3) | ((instr >> 3) & 0x1FFFFC);
+
+ /* Only convert values in the range +/-512 MiB. */
+ if ((addr + 0x020000) & 0x1C0000)
+ continue;
+
+ addr -= (s->pos + (uint32_t)i) >> 12;
+
+ instr &= 0x9000001F;
+ instr |= (addr & 3) << 29;
+ instr |= (addr & 0x03FFFC) << 3;
+ instr |= (0U - (addr & 0x020000)) & 0xE00000;
+
+ put_unaligned_le32(instr, buf + i);
+ }
+ }
+
+ return i;
+}
+#endif
+
/*
* Apply the selected BCJ filter. Update *pos and s->pos to match the amount
* of data that got filtered.
@@ -392,6 +434,11 @@ static void bcj_apply(struct xz_dec_bcj *s,
case BCJ_SPARC:
filtered = bcj_sparc(s, buf, size);
break;
+#endif
+#ifdef XZ_DEC_ARM64
+ case BCJ_ARM64:
+ filtered = bcj_arm64(s, buf, size);
+ break;
#endif
default:
/* Never reached but silence compiler warnings. */
@@ -565,6 +612,9 @@ XZ_EXTERN enum xz_ret xz_dec_bcj_reset(struct xz_dec_bcj *s, uint8_t id)
#endif
#ifdef XZ_DEC_SPARC
case BCJ_SPARC:
+#endif
+#ifdef XZ_DEC_ARM64
+ case BCJ_ARM64:
#endif
break;

diff --git a/lib/xz/xz_private.h b/lib/xz/xz_private.h
index 811add814ae4..307e0de8c260 100644
--- a/lib/xz/xz_private.h
+++ b/lib/xz/xz_private.h
@@ -36,6 +36,9 @@
# ifdef CONFIG_XZ_DEC_SPARC
# define XZ_DEC_SPARC
# endif
+# ifdef CONFIG_XZ_DEC_ARM64
+# define XZ_DEC_ARM64
+# endif
# ifdef CONFIG_XZ_DEC_MICROLZMA
# define XZ_DEC_MICROLZMA
# endif
@@ -97,9 +100,9 @@
*/
#ifndef XZ_DEC_BCJ
# if defined(XZ_DEC_X86) || defined(XZ_DEC_POWERPC) \
- || defined(XZ_DEC_IA64) || defined(XZ_DEC_ARM) \
+ || defined(XZ_DEC_IA64) \
|| defined(XZ_DEC_ARM) || defined(XZ_DEC_ARMTHUMB) \
- || defined(XZ_DEC_SPARC)
+ || defined(XZ_DEC_SPARC) || defined(XZ_DEC_ARM64)
# define XZ_DEC_BCJ
# endif
#endif
--
2.45.2