libbacktrace: support window size in zstd decompression

Reportedly this occurs on AerynOS.

Patch from Ivan Molodetskikh.

	* elf.c (elf_zstd_decompress_frame): Support a compressed block
	that does not set the single segment flag.
	* zstdtest.c (tests): Add tests without single segment.

elf.c

@@ -4364,6 +4364,7 @@ elf_zstd_decompress_frame (const unsigned char **ppin,
   uint32_t repeated_offset3;
   uint16_t *scratch;
   unsigned char hdr;
+  int single_segment;
   int has_checksum;
   uint64_t content_size;
   int last_block;
@@ -4422,12 +4423,18 @@ elf_zstd_decompress_frame (const unsigned char **ppin,
 
   hdr = *pin++;
 
-  /* We expect a single frame.  */
+  single_segment = (hdr & (1 << 5)) != 0;
-  if (unlikely ((hdr & (1 << 5)) == 0))
+  if (!single_segment)
+    {
+      if (unlikely (pin >= pinend))
 	{
 	  elf_uncompress_failed ();
 	  return 0;
 	}
+      /* We have all the data in memory, so we can ignore the window
+	 size.  */
+      pin++;
+    }
   /* Reserved bit must be zero.  */
   if (unlikely ((hdr & (1 << 3)) != 0))
     {
@@ -4444,12 +4451,21 @@ elf_zstd_decompress_frame (const unsigned char **ppin,
   switch (hdr >> 6)
     {
     case 0:
+      if (!single_segment)
+	{
+	  /* The content_size is not specified, but we know it from the
+	     section header.  */
+	  content_size = (uint64_t) sout;
+	}
+      else
+	{
 	  if (unlikely (pin >= pinend))
 	    {
 	      elf_uncompress_failed ();
 	      return 0;
 	    }
 	  content_size = (uint64_t) *pin++;
+	}
       break;
     case 1:
       if (unlikely (pin + 1 >= pinend))

zstdtest.c

@@ -182,7 +182,32 @@ static const struct zstd_test tests[] =
      "\xb4\x21\x45\x3b\x10\xe4\x7b\x99\x4d\x8a\x36\x64\x5c\x77\x08\x02"
      "\xcb\xe0\xce"),
     179,
-  }
+  },
+  {
+    "window-descriptor",
+    "hello, world\n",
+    0,
+    ("\x28\xb5\x2f\xfd"
+     "\x04" /* no Single_Segment_flag; Frame_Content_Size_flag = 0 */
+     "\x00" /* Window_Descriptor */
+     "\x69\x00\x00"
+     "\x68\x65\x6c\x6c\x6f\x2c\x20\x77\x6f\x72\x6c\x64\x0a"
+     "\x4c\x1f\xf9\xf1"),
+    26,
+  },
+  {
+    "window-descriptor-and-content-size",
+    "hello, world\n",
+    0,
+    ("\x28\xb5\x2f\xfd"
+     "\x84" /* no Single_Segment_flag; Frame_Content_Size_flag = 2 */
+     "\x00" /* Window_Descriptor */
+     "\x0d\x00\x00\x00" /* Frame_Content_Size */
+     "\x69\x00\x00"
+     "\x68\x65\x6c\x6c\x6f\x2c\x20\x77\x6f\x72\x6c\x64\x0a"
+     "\x4c\x1f\xf9\xf1"),
+    30,
+  },
 };
 
 /* Test the hand coded samples.  */
@@ -217,7 +242,7 @@ test_samples (struct backtrace_state *state)
 				      error_callback_compress, NULL,
 				      uncompressed, uncompressed_len))
 	{
-	  fprintf (stderr, "test %s: uncompress failed\n", tests[i].name);
+	  fprintf (stderr, "FAIL: test %s: uncompress failed\n", tests[i].name);
 	  ++failures;
 	}
       else
@@ -227,7 +252,7 @@ test_samples (struct backtrace_state *state)
 	    {
 	      size_t j;
 
-	      fprintf (stderr, "test %s: uncompressed data mismatch\n",
+	      fprintf (stderr, "FAIL: test %s: uncompressed data mismatch\n",
 		       tests[i].name);
 	      for (j = 0; j < uncompressed_len; ++j)
 		if (tests[i].uncompressed[j] != uncompressed[j])