[V2 34/36] [SFrame-V3] include: libsframe: remove SFRAME_F_FRAME_POINTER flag

[Indu Bhagat]

SFrame V3 has 8 precious flag bits, two of which are being used.  More
flag byte (s) can be added to the auxiliary header when it comes to
that.  But for now, it may be worthwhile to use the 8-bits frugally.

SFRAME_F_FRAME_POINTER flag bit was added with the intention of marking
binaries built with frame-pointer preserved.  A stack tracer could then
use this (deterministic) information if necessary.  But such a marking
of binary will ideally be done by the linker, and ATM adding such a
framework is not justified for such small gain.  The outcome of this is
that SFRAME_F_FRAME_POINTER is never set in SFrame V2 binaries.

Remove the definition SFRAME_F_FRAME_POINTER for SFrame V3.  The
relinquished bit can be used when reading/dumping SFrame V2 sections are
no longer supported by consumers.  Changing the values of existing flags
like SFRAME_F_FDE_FUNC_START_PCREL is being done for V3, to avoid
version-specific flag bit reading (albeit doable) in consumers.

Related changes to the specification are done in a subsequent commit.

include/
	* sframe.h (SFRAME_V3_F_ALL_FLAGS): Remove
	SFRAME_F_FRAME_POINTER from the set of V3 flags.

libsframe/
	* sframe-dump.c (dump_sframe_header_flags): Add a comment for
	clarity.

---
[New in V2]
---
 include/sframe.h        | 3 +--
 libsframe/sframe-dump.c | 2 ++
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/sframe.h b/include/sframe.h
index 07565e167d6..aea589e8704 100644
--- a/include/sframe.h
+++ b/include/sframe.h
@@ -100,8 +100,7 @@ extern "C"
 
 /* Set of all defined flags in SFrame V3.  */
 #define SFRAME_V3_F_ALL_FLAGS \
-  (SFRAME_F_FDE_SORTED | SFRAME_F_FRAME_POINTER \
-   | SFRAME_F_FDE_FUNC_START_PCREL)
+  (SFRAME_F_FDE_SORTED | SFRAME_F_FDE_FUNC_START_PCREL)
 
 #define SFRAME_CFA_FIXED_FP_INVALID 0
 #define SFRAME_CFA_FIXED_RA_INVALID 0
diff --git a/libsframe/sframe-dump.c b/libsframe/sframe-dump.c
index afc2394e4ad..3153424b0a1 100644
--- a/libsframe/sframe-dump.c
+++ b/libsframe/sframe-dump.c
@@ -161,6 +161,8 @@ dump_sframe_header_flags (const sframe_decoder_ctx *sfd_ctx)
     }
 
   PRINT_FLAG (SFRAME_F_FDE_SORTED);
+  /* Support dumping of both SFrame V2 and V3.  Include SFRAME_F_FRAME_POINTER,
+     even though this should not appear in SFrame V3.  */
   PRINT_FLAG (SFRAME_F_FRAME_POINTER);
   PRINT_FLAG (SFRAME_F_FDE_FUNC_START_PCREL);
 #undef PRINT_FLAG
-- 
2.43.0