From d6bc6b1d8abc5af86ececa9d490a1a1da03dbf02 Mon Sep 17 00:00:00 2001
From: Rob Landley <rob@landley.net>
Date: Sun, 22 Jun 2025 20:50:24 -0500
Subject: [PATCH] Add ARM64 BCJ decoder, from Lassee Collin's xz-embedded
 commit 89094f05f02b

---
 toys/pending/xzcat.c | 44 +++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 43 insertions(+), 1 deletion(-)

diff --git a/toys/pending/xzcat.c b/toys/pending/xzcat.c
index f3417bd7..e1dbfc6e 100644
--- a/toys/pending/xzcat.c
+++ b/toys/pending/xzcat.c
@@ -162,7 +162,8 @@ 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;
 
   /* Return value of the next filter in the chain. We need to preserve
@@ -453,6 +454,43 @@ static size_t bcj_sparc(struct xz_dec_bcj *s, char *buf, size_t size)
   return i;
 }
 
+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;
+
+  for (i = 0; i + 4 <= 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;
+}
+
 /*
  * Apply the selected BCJ filter. Update *pos and s->pos to match the amount
  * of data that got filtered.
@@ -488,6 +526,9 @@ static void bcj_apply(struct xz_dec_bcj *s,
   case BCJ_SPARC:
     filtered = bcj_sparc(s, buf, size);
     break;
+  case BCJ_ARM64:
+    filtered = bcj_arm64(s, buf, size);
+    break;
   default:
     /* Never reached but silence compiler warnings. */
     filtered = 0;
@@ -639,6 +680,7 @@ enum xz_ret xz_dec_bcj_run(struct xz_dec_bcj *s, struct xz_dec_lzma2 *lzma2,
  */
 enum xz_ret xz_dec_bcj_reset(struct xz_dec_bcj *s, char id)
 {
+  if (id<BCJ_X86 || id>BCJ_ARM64) return XZ_OPTIONS_ERROR;
   s->type = id;
   s->ret = XZ_OK;
   s->pos = 0;
-- 
2.39.5