1 files changed, 137 insertions, 0 deletions
diff --git a/src/liblzma/simple/arm64.c b/src/liblzma/simple/arm64.c
new file mode 100644
index 0000000..0fe0824
--- /dev/null
+++ b/src/liblzma/simple/arm64.c
@@ -0,0 +1,137 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+/// \file       arm64.c
+/// \brief      Filter for ARM64 binaries
+///
+/// This converts ARM64 relative addresses in the BL and ADRP immediates
+/// to absolute values to increase redundancy of ARM64 code.
+///
+/// Converting B or ADR instructions was also tested but it's not useful.
+/// A majority of the jumps for the B instruction are very small (+/- 0xFF).
+/// These are typical for loops and if-statements. Encoding them to their
+/// absolute address reduces redundancy since many of the small relative
+/// jump values are repeated, but very few of the absolute addresses are.
+//
+//  Authors:    Lasse Collin
+//              Jia Tan
+//              Igor Pavlov
+//
+//  This file has been put into the public domain.
+//  You can do whatever you want with this file.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#include "simple_private.h"
+
+
+static size_t
+arm64_code(void *simple lzma_attribute((__unused__)),
+		uint32_t now_pos, bool is_encoder,
+		uint8_t *buffer, size_t size)
+{
+	size_t i;
+
+	// Clang 14.0.6 on x86-64 makes this four times bigger and 40 % slower
+	// with auto-vectorization that is enabled by default with -O2.
+	// Such vectorization bloat happens with -O2 when targeting ARM64 too
+	// but performance hasn't been tested.
+#ifdef __clang__
+#	pragma clang loop vectorize(disable)
+#endif
+	for (i = 0; i + 4 <= size; i += 4) {
+		uint32_t pc = (uint32_t)(now_pos + i);
+		uint32_t instr = read32le(buffer + i);
+
+		if ((instr >> 26) == 0x25) {
+			// BL instruction:
+			// The full 26-bit immediate is converted.
+			// The range is +/-128 MiB.
+			//
+			// Using the full range is helps quite a lot with
+			// big executables. Smaller range would reduce false
+			// positives in non-code sections of the input though
+			// so this is a compromise that slightly favors big
+			// files. With the full range only six bits of the 32
+			// need to match to trigger a conversion.
+			const uint32_t src = instr;
+			instr = 0x94000000;
+
+			pc >>= 2;
+			if (!is_encoder)
+				pc = 0U - pc;
+
+			instr |= (src + pc) & 0x03FFFFFF;
+			write32le(buffer + i, instr);
+
+		} else if ((instr & 0x9F000000) == 0x90000000) {
+			// ADRP instruction:
+			// Only values in the range +/-512 MiB are converted.
+			//
+			// Using less than the full +/-4 GiB range reduces
+			// false positives on non-code sections of the input
+			// while being excellent for executables up to 512 MiB.
+			// The positive effect of ADRP conversion is smaller
+			// than that of BL but it also doesn't hurt so much in
+			// non-code sections of input because, with +/-512 MiB
+			// range, nine bits of 32 need to match to trigger a
+			// conversion (two 10-bit match choices = 9 bits).
+			const uint32_t src = ((instr >> 29) & 3)
+					| ((instr >> 3) & 0x001FFFFC);
+
+			// With the addition only one branch is needed to
+			// check the +/- range. This is usually false when
+			// processing ARM64 code so branch prediction will
+			// handle it well in terms of performance.
+			//
+			//if ((src & 0x001E0000) != 0
+			// && (src & 0x001E0000) != 0x001E0000)
+			if ((src + 0x00020000) & 0x001C0000)
+				continue;
+
+			instr &= 0x9000001F;
+
+			pc >>= 12;
+			if (!is_encoder)
+				pc = 0U - pc;
+
+			const uint32_t dest = src + pc;
+			instr |= (dest & 3) << 29;
+			instr |= (dest & 0x0003FFFC) << 3;
+			instr |= (0U - (dest & 0x00020000)) & 0x00E00000;
+			write32le(buffer + i, instr);
+		}
+	}
+
+	return i;
+}
+
+
+static lzma_ret
+arm64_coder_init(lzma_next_coder *next, const lzma_allocator *allocator,
+		const lzma_filter_info *filters, bool is_encoder)
+{
+	return lzma_simple_coder_init(next, allocator, filters,
+			&arm64_code, 0, 4, 4, is_encoder);
+}
+
+
+#ifdef HAVE_ENCODER_ARM64
+extern lzma_ret
+lzma_simple_arm64_encoder_init(lzma_next_coder *next,
+		const lzma_allocator *allocator,
+		const lzma_filter_info *filters)
+{
+	return arm64_coder_init(next, allocator, filters, true);
+}
+#endif
+
+
+#ifdef HAVE_DECODER_ARM64
+extern lzma_ret
+lzma_simple_arm64_decoder_init(lzma_next_coder *next,
+		const lzma_allocator *allocator,
+		const lzma_filter_info *filters)
+{
+	return arm64_coder_init(next, allocator, filters, false);
+}
+#endif