[PATCH 06/10] perf jevents: Add --compress=lzma block compression backend

[Ian Rogers <irogers@google.com>]

Add an 'lzma' block-indexed string compression backend to jevents.py
using Python's standard-library lzma module (imported lazily) to
compress each ~8 KiB string block independently as a raw LZMA2 stream
(FORMAT_RAW + FILTER_LZMA2, dict_size=64 KiB) decoded on demand via
liblzma's lzma_raw_buffer_decode() in pmu-events-string.c.

This provides random-access per-block string decompression indexed by
(block_id << 16) | sub_offset on builds where liblzma is enabled without
libzstd or zlib. On x86, --compress=lzma shrinks pmu-events-string.o
from ~6.90 MB to ~819 KB.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/pmu-events/jevents.py | 44 ++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/tools/perf/pmu-events/jevents.py b/tools/perf/pmu-events/jevents.py
index ec7d460a32b6..a7fad9bbf7b4 100755
--- a/tools/perf/pmu-events/jevents.py
+++ b/tools/perf/pmu-events/jevents.py
@@ -238,10 +238,54 @@ def _compress_blocks_zlib(blocks: Sequence[bytes]) -> Optional[CompressedStringO
   )
 
 
+def _compress_blocks_lzma(blocks: Sequence[bytes]) -> Optional[CompressedStringOutput]:
+  """Compress blocks using stdlib lzma raw LZMA2 streams."""
+  try:
+    lzma_mod = importlib.import_module('lzma')
+  except ImportError:
+    return None
+
+  dict_size = 1 << _BIG_C_STRING_BLOCK_SHIFT
+  filters = [{'id': lzma_mod.FILTER_LZMA2, 'preset': 6, 'dict_size': dict_size}]
+  compressed_blocks = [
+      lzma_mod.compress(block, format=lzma_mod.FORMAT_RAW, filters=filters)
+      for block in blocks
+  ]
+
+  decompress_fn = f"""static bool decompress_block(const unsigned char *src, uint32_t src_len,
+\t\t\t     char *dst, uint32_t dst_len)
+{{
+\tlzma_options_lzma opt = {{
+\t\t.dict_size = {dict_size}U,
+\t\t.preset_dict = NULL,
+\t\t.preset_dict_size = 0,
+\t}};
+\tconst lzma_filter filters[] = {{
+\t\t{{ .id = LZMA_FILTER_LZMA2, .options = &opt }},
+\t\t{{ .id = LZMA_VLI_UNKNOWN, .options = NULL }},
+\t}};
+\tsize_t in_pos = 0, out_pos = 0;
+\tlzma_ret ret;
+
+\tret = lzma_raw_buffer_decode(filters, NULL, src, &in_pos, src_len,
+\t\t\t\t     (uint8_t *)dst, &out_pos, dst_len);
+\treturn ret == LZMA_OK && in_pos == src_len && out_pos == dst_len;
+}}
+"""
+  return CompressedStringOutput(
+      name='lzma',
+      c_headers=['<lzma.h>'],
+      compressed_blocks=compressed_blocks,
+      extra_c_decls='',
+      decompress_c_fn=decompress_fn,
+  )
+
+
 _COMPRESS_BACKENDS: Dict[
     str, Optional[Callable[[Sequence[bytes]], Optional[CompressedStringOutput]]]
 ] = {
     'none': None,
+    'lzma': _compress_blocks_lzma,
     'zlib': _compress_blocks_zlib,
 }
 
-- 
2.56.1.703.gf848ed807c-goog