[PATCH] livepatch/klp-build: Require Clang assembler >= 20

[Josh Poimboeuf]

Some special sections specify their ELF section entsize, for example:

  .pushsection section, "M", @progbits, 8

The entsize (8 in this example) is needed by objtool klp-diff for
extracting individual entries.

Clang assembler versions older than 20 silently ignore the above
construct and set entsize to 0, resulting in the following error:

  .discard.annotate_data: missing special section entsize or annotations

Add a klp-build check to prevent the use of Clang assembler versions
prior to 20.

Fixes: 24ebfcd65a87 ("livepatch/klp-build: Introduce klp-build script for 
generating livepatch modules")
Reported-by: Song Liu <s...@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoim...@kernel.org>
---
For tip/objtool/urgent.

 scripts/livepatch/klp-build | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/scripts/livepatch/klp-build b/scripts/livepatch/klp-build
index a73515a82272..809e198a561d 100755
--- a/scripts/livepatch/klp-build
+++ b/scripts/livepatch/klp-build
@@ -249,6 +249,10 @@ validate_config() {
        [[ -v CONFIG_GCC_PLUGIN_RANDSTRUCT ]] &&        \
                die "kernel option 'CONFIG_GCC_PLUGIN_RANDSTRUCT' not supported"
 
+       [[ -v CONFIG_AS_IS_LLVM ]] &&                           \
+               [[ "$CONFIG_AS_VERSION" -lt 200000 ]] &&        \
+               die "Clang assembler version < 20 not supported"
+
        return 0
 }
 
-- 
2.52.0