tools/gn: update reference.md doc

tools/gn/docs/reference.md

 # GN Reference
 
 *This page is automatically generated from* `gn help --markdown all`.
 
 ## **\--args**: Specifies build arguments overrides.
 
 ```
   See "gn help buildargs" for an overview of how build arguments work.
 
   Most operations take a build directory. The build arguments are taken
@@ skipping 1413 matching lines @@
       match the value of the "root_gen_dir" variable when inside that
       target's declaration.
 
   "target_out_dir
       The output directory for the target. This will match the
       value of the "target_out_dir" variable when inside that target's
       declaration.
 
   "root_out_dir"
       The root of the output file tree for the target. This will
-      match the value of the "root_gen_dir" variable when inside that
+      match the value of the "root_out_dir" variable when inside that
       target's declaration.
 
   "label_no_toolchain"
       The fully qualified version of this label, not including the
       toolchain. For the input ":bar" it might return
       "//foo:bar".
 
   "label_with_toolchain"
       The fully qualified version of this label, including the
       toolchain. For the input ":bar" it might return
@@ skipping 1854 matching lines @@
 
 ```
   For action and action_foreach targets, args is the list of arguments
   to pass to the script. Typically you would use source expansion (see
   "gn help source_expansion") to insert the source file names.
 
   See also "gn help action" and "gn help action_foreach".
 
 
 ```
+## **asmflags**: Flags passed to the assembler.
+
+```
+  A list of strings.
+
+  "asmflags" are passed to any invocation of a tool that takes an
+  .asm or .S file as input.
+
+```
+
+### **Ordering of flags and values**
+
+```
+  1. Those set on the current target (not in a config).
+  2. Those set on the "configs" on the target in order that the
+     configs appear in the list.
+  3. Those set on the "all_dependent_configs" on the target in order
+     that the configs appear in the list.
+  4. Those set on the "public_configs" on the target in order that
+     those configs appear in the list.
+  5. all_dependent_configs pulled from dependencies, in the order of
+     the "deps" list. This is done recursively. If a config appears
+     more than once, only the first occurance will be used.
+  6. public_configs pulled from dependencies, in the order of the
+     "deps" list. If a dependency is public, they will be applied
+     recursively.
+
+
+```
 ## **cflags***: Flags passed to the C compiler.
 
 ```
   A list of strings.
 
   "cflags" are passed to all invocations of the C, C++, Objective C,
   and Objective C++ compilers.
 
   To target one of these variants individually, use "cflags_c",
   "cflags_cc", "cflags_objc", and "cflags_objcc",
-  respectively.
+  respectively. These variant-specific versions of cflags* will be
+  appended on the compiler command line after "cflags".
 
-  These variant-specific versions of cflags* will be appended to the
-  "cflags".
+  See also "asmflags" for flags for assembly-language files.
 
 ```
 
 ### **Ordering of flags and values**
 
 ```
   1. Those set on the current target (not in a config).
   2. Those set on the "configs" on the target in order that the
      configs appear in the list.
   3. Those set on the "all_dependent_configs" on the target in order
@@ skipping 12 matching lines @@
 ## **cflags***: Flags passed to the C compiler.
 
 ```
   A list of strings.
 
   "cflags" are passed to all invocations of the C, C++, Objective C,
   and Objective C++ compilers.
 
   To target one of these variants individually, use "cflags_c",
   "cflags_cc", "cflags_objc", and "cflags_objcc",
-  respectively.
+  respectively. These variant-specific versions of cflags* will be
+  appended on the compiler command line after "cflags".
 
-  These variant-specific versions of cflags* will be appended to the
-  "cflags".
+  See also "asmflags" for flags for assembly-language files.
 
 ```
 
 ### **Ordering of flags and values**
 
 ```
   1. Those set on the current target (not in a config).
   2. Those set on the "configs" on the target in order that the
      configs appear in the list.
   3. Those set on the "all_dependent_configs" on the target in order
@@ skipping 12 matching lines @@
 ## **cflags***: Flags passed to the C compiler.
 
 ```
   A list of strings.
 
   "cflags" are passed to all invocations of the C, C++, Objective C,
   and Objective C++ compilers.
 
   To target one of these variants individually, use "cflags_c",
   "cflags_cc", "cflags_objc", and "cflags_objcc",
-  respectively.
+  respectively. These variant-specific versions of cflags* will be
+  appended on the compiler command line after "cflags".
 
-  These variant-specific versions of cflags* will be appended to the
-  "cflags".
+  See also "asmflags" for flags for assembly-language files.
 
 ```
 
 ### **Ordering of flags and values**
 
 ```
   1. Those set on the current target (not in a config).
   2. Those set on the "configs" on the target in order that the
      configs appear in the list.
   3. Those set on the "all_dependent_configs" on the target in order
@@ skipping 12 matching lines @@
 ## **cflags***: Flags passed to the C compiler.
 
 ```
   A list of strings.
 
   "cflags" are passed to all invocations of the C, C++, Objective C,
   and Objective C++ compilers.
 
   To target one of these variants individually, use "cflags_c",
   "cflags_cc", "cflags_objc", and "cflags_objcc",
-  respectively.
+  respectively. These variant-specific versions of cflags* will be
+  appended on the compiler command line after "cflags".
 
-  These variant-specific versions of cflags* will be appended to the
-  "cflags".
+  See also "asmflags" for flags for assembly-language files.
 
 ```
 
 ### **Ordering of flags and values**
 
 ```
   1. Those set on the current target (not in a config).
   2. Those set on the "configs" on the target in order that the
      configs appear in the list.
   3. Those set on the "all_dependent_configs" on the target in order
@@ skipping 12 matching lines @@
 ## **cflags***: Flags passed to the C compiler.
 
 ```
   A list of strings.
 
   "cflags" are passed to all invocations of the C, C++, Objective C,
   and Objective C++ compilers.
 
   To target one of these variants individually, use "cflags_c",
   "cflags_cc", "cflags_objc", and "cflags_objcc",
-  respectively.
+  respectively. These variant-specific versions of cflags* will be
+  appended on the compiler command line after "cflags".
 
-  These variant-specific versions of cflags* will be appended to the
-  "cflags".
+  See also "asmflags" for flags for assembly-language files.
 
 ```
 
 ### **Ordering of flags and values**
 
 ```
   1. Those set on the current target (not in a config).
   2. Those set on the "configs" on the target in order that the
      configs appear in the list.
   3. Those set on the "all_dependent_configs" on the target in order
@@ skipping 1699 matching lines @@
 **  -q**: Quiet mode. Don't print output on success.
 **  \--root**: Explicitly specify source root.
 **  \--runtime-deps-list-file**: Save runtime dependencies for targets in file.
 **  \--threads**: Specify number of worker threads.
 **  \--time**: Outputs a summary of how long everything took.
 **  \--tracelog**: Writes a Chrome-compatible trace log to the given file.
 **  -v**: Verbose logging.
 **  \--version**: Prints the GN version number and exits.
 
 ```