gas: add new command line option --scfi=experimental

When the command line option --scfi=experimenta is passed to the GNU
assembler, it will synthesize DWARF call frame information (CFI) for the
input assembly.

The option --scfi=experimental will also ignore most of the existing
.cfi_* directives, if already contained in the provided input file.
Only the following CFI directives will not be ignored:
  - .cfi_sections,
  - .cfi_label,
  - .cfi_signal_frame

To use SCFI, a target will need to:
    - define TARGET_USE_SCFI and TARGET_USE_GINSN, and other necessary
    definitions,
    - provide means to help GAS understand the target specific instruction
    semantics by creating ginsns.

The upcoming support for SCFI is inteded to be experimental, hence the
option --scfi=experimental.  The --scfi= may see more options like
--scfi=[all,none] added in future, once the SCFI support in GAS is
mature and robust.  The offering may also see for example, an
--scfi=inline option for dealing with inline asm may be added in the
future.  In --scfi=inline option, the GNU assembler may consume (and not
ignore) the compiler generated CFI for the code surrounding the inline
asm.

Also document the option.

gas/
        * as.c (show_usage): Add support for --scfi=experimental.
        (parse_args): Likewise.
        * as.h (enum synth_cfi_type): Define new type.
        * doc/as.texi: Document the new option.

1 files changed, 8 insertions, 0 deletions

diff --git a/gas/as.h b/gas/as.h
index 1297e3d..69d7ae2 100644
--- a/gas/as.h
+++ b/gas/as.h
@@ -324,6 +324,14 @@ COMMON int flag_fatal_warnings; /* --fatal-warnings */
    are detected.  */
 COMMON unsigned char flag_always_generate_output; /* -Z */
 
+enum synth_cfi_type
+{
+  SYNTH_CFI_NONE = 0,
+  SYNTH_CFI_EXPERIMENTAL,
+};
+
+COMMON enum synth_cfi_type flag_synth_cfi;
+
 /* This is true if the assembler should output time and space usage.  */
 COMMON unsigned char flag_print_statistics;