[RFC PATCH v4 4/6] objtool/powerpc: Skip jump destination analysis and unnanotated intra-function call warnings for --ftr-fixup

[Sathvika Vasireddy <sv@linux.ibm.com>]

Objtool is throwing unannotated intra-function call warnings
when run on vmlinux with --ftr-fixup option.

One such example:

vmlinux: warning: objtool: .text+0x3d94:
                        unannotated intra-function call

.text + 0x3d94 = c000000000008000 + 3d94 = c0000000000081d4

c0000000000081d4: 45 24 02 48  bl c00000000002a618
<system_reset_exception+0x8>

c00000000002a610 <system_reset_exception>:
c00000000002a610:       0e 01 4c 3c     addis   r2,r12,270
                        c00000000002a610: R_PPC64_REL16_HA    .TOC.
c00000000002a614:       f0 6c 42 38     addi    r2,r2,27888
                        c00000000002a614: R_PPC64_REL16_LO    .TOC.+0x4
c00000000002a618:       a6 02 08 7c     mflr    r0

This is happening because we should be looking for destination
symbols that are at absolute offsets instead of relative offsets.
After fixing dest_off to point to absolute offset, there are still
a lot of these warnings shown.

In the above example, objtool is computing the destination
offset to be c00000000002a618, which points to a completely
different instruction. find_call_destination() is looking for this
offset and failing. Instead, we should be looking for destination
offset c00000000002a610 which points to system_reset_exception
function.

Even after fixing the way destination offset is computed, and
after looking for dest_off - 0x8 in cases where the original offset
is not found, there are still a lot of unannotated intra-function
call warnings generated. This is due to symbols that are not
properly annotated.

So, for now, as a hack to curb these warnings, do not emit
unannotated intra-function call warnings when objtool is run
with --ftr-fixup option.

Skip add_jump_destinations() and suppress intra-function call
errors in --ftr-fixup mode. The feature fixup pass only needs fixup
entry tables, relocation entries from .__ftr_alternates.text, and
elf_write_insn() to patch branch offsets.

Signed-off-by: Sathvika Vasireddy <sv@linux.ibm.com>
---
 tools/objtool/check.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 7b95ddb0460d..ba194446df0a 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1599,7 +1599,6 @@ static int add_jump_destinations(struct objtool_file *file)
 			    dest_off == func->offset + func->len)
 				continue;
 
-
 			ERROR_INSN(insn, "can't find jump dest instruction at %s",
 				offstr(dest_sec, dest_off));
 			return -1;
@@ -1681,7 +1680,7 @@ static int add_call_destinations(struct objtool_file *file)
 			if (func && func->ignore)
 				continue;
 
-			if (!insn_call_dest(insn)) {
+			if (!insn_call_dest(insn) && !opts.ftr_fixup) {
 				ERROR_INSN(insn, "unannotated intra-function call");
 				return -1;
 			}
@@ -2637,8 +2636,10 @@ static int decode_sections(struct objtool_file *file)
 			return -1;
 	}
 
-	if (add_jump_destinations(file))
-		return -1;
+	if (!opts.ftr_fixup) {
+		if (add_jump_destinations(file))
+			return -1;
+	}
 
 	/*
 	 * Must be before add_call_destination(); it changes INSN_CALL to
-- 
2.43.0