kbuild: lto: Merge module sections if and only if CONFIG_LTO_CLANG is enabled

stable inclusion
from stable-v5.10.102
commit 44b81136e86849117f34a083c359e4860662b3be
bugzilla: https://gitee.com/openeuler/kernel/issues/I567K6

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=44b81136e86849117f34a083c359e4860662b3be

--------------------------------

commit 6a3193cd upstream.

Merge module sections only when using Clang LTO. With ld.bfd, merging
sections does not appear to update the symbol tables for the module,
e.g. 'readelf -s' shows the value that a symbol would have had, if
sections were not merged. ld.lld does not show this problem.

The stale symbol table breaks gdb's function disassembler, and presumably
other things, e.g.

  gdb -batch -ex "file arch/x86/kvm/kvm.ko" -ex "disassemble kvm_init"

reads the wrong bytes and dumps garbage.

Fixes: dd277622 ("kbuild: lto: merge module sections")
Cc: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: NSean Christopherson <seanjc@google.com>
Reviewed-by: NSami Tolvanen <samitolvanen@google.com>
Tested-by: NSami Tolvanen <samitolvanen@google.com>
Signed-off-by: NKees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210322234438.502582-1-seanjc@google.com
Cc: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NYu Liao <liaoyu15@huawei.com>
Reviewed-by: NWei Li <liwei391@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

scripts/module.lds.S

@@ -27,6 +27,7 @@ SECTIONS {
 
 	__patchable_function_entries : { *(__patchable_function_entries) }
 
+#ifdef CONFIG_LTO_CLANG
 	/*
 	 * With CONFIG_LTO_CLANG, LLD always enables -fdata-sections and
 	 * -ffunction-sections, which increases the size of the final module.
@@ -48,6 +49,7 @@ SECTIONS {
 	}
 
 	.text : { *(.text .text.[0-9a-zA-Z_]*) }
+#endif
 }
 
 /* bring in arch-specific sections */