[Devel] [PATCH RHEL8 COMMIT] ms/objtool: Don't fail on missing symbol table

[Konstantin Khorenko]

The commit is pushed to "branch-rh8-4.18.0-305.3.1.vz8.7.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh8-4.18.0-305.3.1.vz8.7.11
------>
commit 1e4ad734b7b1a677ce6aad618916f9de37649304
Author: Josh Poimboeuf <jpoimboe at redhat.com>
Date:   Fri Sep 10 20:13:21 2021 +0300

    ms/objtool: Don't fail on missing symbol table
    
    ms commit 1d489151e9f9
    
    Thanks to a recent binutils change which doesn't generate unused
    symbols, it's now possible for thunk_64.o be completely empty without
    CONFIG_PREEMPTION: no text, no data, no symbols.
    
    We could edit the Makefile to only build that file when
    CONFIG_PREEMPTION is enabled, but that will likely create confusion
    if/when the thunks end up getting used by some other code again.
    
    Just ignore it and move on.
    
    Reported-by: Nathan Chancellor <natechancellor at gmail.com>
    Reviewed-by: Nathan Chancellor <natechancellor at gmail.com>
    Reviewed-by: Miroslav Benes <mbenes at suse.cz>
    Tested-by: Nathan Chancellor <natechancellor at gmail.com>
    Link: https://github.com/ClangBuiltLinux/linux/issues/1254
    Signed-off-by: Josh Poimboeuf <jpoimboe at redhat.com>
    Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
---
 tools/objtool/elf.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 5074163adf63..6a621c33e017 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -224,8 +224,11 @@ static int read_symbols(struct elf *elf)
 
 	symtab = find_section_by_name(elf, ".symtab");
 	if (!symtab) {
-		WARN("missing symbol table");
-		return -1;
+		/*
+		 * A missing symbol table is actually possible if it's an empty
+		 * .o file.  This can happen for thunk_64.o.
+		 */
+		return 0;
 	}
 
 	symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;