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[PATCH,RFC 5/9] gas: add new command line option --scfi[=all,none]

Indu Bhagat indu.bhagat@oracle.com
Wed Sep 20 23:03:57 GMT 2023 
When the command line option --scfi (default is --scfi=all) is passed to
the GNU assembler, it will synthesize DWARF call frame information (CFI)
for the assembly.

The option --scfi=all ignores any existing .cfi_* directives already
contained in the provided assembler file.

To use SCFI, a target will need to:
    - define TARGET_USE_SCFI and TARGET_USE_GINSN, and other necessary
    definitions,
    - provide implementation of some APIs to help GAS understand the
    target specific semantics.

The --scfi=[all,none] may see more options added in future.  For
example, --scfi=inline, for dealing with inline asm may be added in the
future.  In this option, the GNU assembler will consume (and not ignore)
the compiler generated CFI for the code surrounding the inline asm.

Also document the option.

gas/
        * as.c (parse_args): Add support for --scfi.
        * as.h (enum synth_cfi_type): Define new type.
        * doc/as.texi: Document the new option.
---
 gas/as.c        | 20 +++++++++++++++++++-
 gas/as.h        |  8 ++++++++
 gas/doc/as.texi |  5 +++++
 3 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/gas/as.c b/gas/as.c
index 6839c841588..523169e66e3 100644
--- a/gas/as.c
+++ b/gas/as.c
@@ -372,6 +372,11 @@ Options:\n\
   -R                      fold data section into text section\n"));
   fprintf (stream, _("\
   --reduce-memory-overheads ignored\n"));
+# ifdef TARGET_USE_SCFI
+  fprintf (stream, _("\
+  --scfi=[all,none]	  synthesize DWARF CFI for hand-written asm (not inline)\n\
+			  (default --scfi=all)\n"));
+# endif
   fprintf (stream, _("\
   --statistics            print various measured statistics from execution\n"));
   fprintf (stream, _("\
@@ -511,7 +516,8 @@ parse_args (int * pargc, char *** pargv)
       OPTION_NOCOMPRESS_DEBUG,
       OPTION_NO_PAD_SECTIONS,
       OPTION_MULTIBYTE_HANDLING,  /* = STD_BASE + 40 */
-      OPTION_SFRAME
+      OPTION_SFRAME,
+      OPTION_SCFI
     /* When you add options here, check that they do
        not collide with OPTION_MD_BASE.  See as.h.  */
     };
@@ -586,6 +592,9 @@ parse_args (int * pargc, char *** pargv)
     ,{"no-pad-sections", no_argument, NULL, OPTION_NO_PAD_SECTIONS}
     ,{"no-warn", no_argument, NULL, 'W'}
     ,{"reduce-memory-overheads", no_argument, NULL, OPTION_REDUCE_MEMORY_OVERHEADS}
+#ifdef TARGET_USE_SCFI
+    ,{"scfi", no_argument, NULL, OPTION_SCFI}
+#endif
     ,{"statistics", no_argument, NULL, OPTION_STATISTICS}
     ,{"strip-local-absolute", no_argument, NULL, OPTION_STRIP_LOCAL_ABSOLUTE}
     ,{"version", no_argument, NULL, OPTION_VERSION}
@@ -982,6 +991,15 @@ This program has absolutely no warranty.\n"));
 	  flag_execstack = 0;
 	  break;
 
+	case OPTION_SCFI:
+	  if (!optarg || strcasecmp (optarg, "all") == 0)
+	    flag_synth_cfi = SYNTH_CFI_ALL;
+	  else if (strcasecmp (optarg, "none") == 0)
+	    flag_synth_cfi = SYNTH_CFI_NONE;
+	  else
+	    as_fatal (_("Invalid --scfi= option: `%s'"), optarg);
+	  break;
+
 	case OPTION_SIZE_CHECK:
 	  if (strcasecmp (optarg, "error") == 0)
 	    flag_allow_nonconst_size = false;
diff --git a/gas/as.h b/gas/as.h
index 99ffe77afd2..42fc44bd494 100644
--- a/gas/as.h
+++ b/gas/as.h
@@ -322,6 +322,14 @@ 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_ALL,
+};
+
+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;
 
diff --git a/gas/doc/as.texi b/gas/doc/as.texi
index 6a3e5eed39f..c4755721407 100644
--- a/gas/doc/as.texi
+++ b/gas/doc/as.texi
@@ -255,6 +255,7 @@ gcc(1), ld(1), and the Info entries for @file{binutils} and @file{ld}.
  [@b{--multibyte-handling=[allow|warn|warn-sym-only]}]
  [@b{--no-pad-sections}]
  [@b{-o} @var{objfile}] [@b{-R}]
+ [@b{--scfi=[all,none]}]
  [@b{--sectname-subst}]
  [@b{--size-check=[error|warning]}]
  [@b{--statistics}]
@@ -932,6 +933,10 @@ Ignored.  Supported for compatibility with tools that apss the same option to
 both the assembler and the linker.
 
 @ifset ELF
+@item --scfi=all
+@itemx --scfi=none
+Synthesize CFI for hand-written asm.
+
 @item --sectname-subst
 Honor substitution sequences in section names.
 @ifclear man
-- 
2.41.0
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