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kbuild: lto: postpone objtool

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With LTO, LLVM bitcode won't be compiled into native code until
modpost_link, or modfinal for modules. This change postpones calls
to objtool until after these steps, and moves objtool_args to
Makefile.lib, so the arguments can be reused in Makefile.modfinal.

As we didn't have objects to process earlier, we use --duplicate
when processing vmlinux.o. This change also disables unreachable
instruction warnings with LTO to avoid warnings about the int3
padding between functions.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
Sami Tolvanen
2020-04-13 16:10:13 -07:00
committed by Kees Cook
parent 41425ebe20
commit b1a1a1a09b
4 changed files with 55 additions and 26 deletions
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28
scripts/link-vmlinux.sh
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@@ -103,14 +103,36 @@ modpost_link()
objtool_link()
{
local objtoolcmd;
local objtoolopt;
if [ "${CONFIG_LTO_CLANG} ${CONFIG_STACK_VALIDATION}" = "y y" ]; then
# Don't perform vmlinux validation unless explicitly requested,
# but run objtool on vmlinux.o now that we have an object file.
if [ -n "${CONFIG_UNWINDER_ORC}" ]; then
objtoolcmd="orc generate"
fi
objtoolopt="${objtoolopt} --duplicate"
if [ -n "${CONFIG_FTRACE_MCOUNT_USE_OBJTOOL}" ]; then
objtoolopt="${objtoolopt} --mcount"
fi
fi
if [ -n "${CONFIG_VMLINUX_VALIDATION}" ]; then
objtoolopt="check --vmlinux --noinstr"
objtoolopt="${objtoolopt} --noinstr"
fi
if [ -n "${objtoolopt}" ]; then
if [ -z "${objtoolcmd}" ]; then
objtoolcmd="check"
fi
objtoolopt="${objtoolopt} --vmlinux"
if [ -z "${CONFIG_FRAME_POINTER}" ]; then
objtoolopt="${objtoolopt} --no-fp"
fi
if [ -n "${CONFIG_GCOV_KERNEL}" ]; then
if [ -n "${CONFIG_GCOV_KERNEL}" ] || [ -n "${CONFIG_LTO_CLANG}" ]; then
objtoolopt="${objtoolopt} --no-unreachable"
fi
if [ -n "${CONFIG_RETPOLINE}" ]; then
@@ -120,7 +142,7 @@ objtool_link()
objtoolopt="${objtoolopt} --uaccess"
fi
info OBJTOOL ${1}
tools/objtool/objtool ${objtoolopt} ${1}
tools/objtool/objtool ${objtoolcmd} ${objtoolopt} ${1}
fi
}