[PATCH] D42002: [docs] Only LLVM IR bitstreams begin with 'BC'

[Brian Gesiak via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rL322520: [docs] Only LLVM IR bitstreams begin with 'BC' (authored by modocache, committed by ).

Repository:
  rL LLVM

https://reviews.llvm.org/D42002

Files:
  llvm/trunk/docs/BitCodeFormat.rst


Index: llvm/trunk/docs/BitCodeFormat.rst
===================================================================
--- llvm/trunk/docs/BitCodeFormat.rst
+++ llvm/trunk/docs/BitCodeFormat.rst
@@ -62,10 +62,12 @@
 Magic Numbers
 -------------
 
-The first two bytes of a bitcode file are 'BC' (``0x42``, ``0x43``).  The second
-two bytes are an application-specific magic number.  Generic bitcode tools can
-look at only the first two bytes to verify the file is bitcode, while
-application-specific programs will want to look at all four.
+The first four bytes of a bitstream are used as an application-specific magic
+number.  Generic bitcode tools may look at the first four bytes to determine
+whether the stream is a known stream type.  However, these tools should *not*
+determine whether a bitstream is valid based on its magic number alone.  New
+application-specific bitstream formats are being developed all the time; tools
+should not reject them just because they have a hitherto unseen magic number.
 
 .. _primitives:
 
@@ -496,12 +498,9 @@
 The magic number for LLVM IR files is:
 
 :raw-html:`<tt><blockquote>`
-[0x0\ :sub:`4`, 0xC\ :sub:`4`, 0xE\ :sub:`4`, 0xD\ :sub:`4`]
+['B'\ :sub:`8`, 'C'\ :sub:`8`, 0x0\ :sub:`4`, 0xC\ :sub:`4`, 0xE\ :sub:`4`, 0xD\ :sub:`4`]
 :raw-html:`</blockquote></tt>`
 
-When combined with the bitcode magic number and viewed as bytes, this is
-``"BC 0xC0DE"``.
-
 .. _Signed VBRs:
 
 Signed VBRs


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