From 1e3071d629b2e2cd7faeb8de2f88ba31cfd7231a Mon Sep 17 00:00:00 2001 From: Nathan Chancellor Date: Wed, 16 Oct 2024 14:12:38 -0700 Subject: [PATCH] um: Disable auto variable initialization for stub_exe.c When automatic variable initialization is enabled via CONFIG_INIT_STACK_ALL_{PATTERN,ZERO}, clang will insert a call to memset() to initialize an object created with __builtin_alloca(). This ultimately breaks the build when linking stub_exe because it is a standalone executable that does not include or link against memset(). ld: arch/um/kernel/skas/stub_exe.o: in function `_start': arch/um/kernel/skas/stub_exe.c:83:(.ltext+0x15): undefined reference to `memset' Disable automatic variable initialization for stub_exe.c by passing the default value of 'uninitialized' to '-ftrivial-auto-var-init', which avoids generating the call to memset(). This code is small and runs quickly as it is just designed to set up an environment, so stack variable initialization is unnecessary overhead for little gain. Fixes: 32e8eaf263d9 ("um: use execveat to create userspace MMs") Signed-off-by: Nathan Chancellor Link: https://patch.msgid.link/20241016-uml-fix-stub_exe-clang-v1-2-3d6381dc5a78@kernel.org Signed-off-by: Johannes Berg --- arch/um/kernel/skas/Makefile | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/arch/um/kernel/skas/Makefile b/arch/um/kernel/skas/Makefile index f93db893b823..f6a219074772 100644 --- a/arch/um/kernel/skas/Makefile +++ b/arch/um/kernel/skas/Makefile @@ -39,6 +39,11 @@ targets += stub_exe.dbg stub_exe $(stub_exe_objs-y) CFLAGS_stub.o := $(CFLAGS_NO_HARDENING) CFLAGS_stub_exe.o := $(CFLAGS_NO_HARDENING) + +# Clang will call memset() from __builtin_alloca() when stack variable +# initialization is enabled, which is used in stub_exe.c. +CFLAGS_stub_exe.o += $(call cc-option, -ftrivial-auto-var-init=uninitialized) + UNPROFILE_OBJS := stub.o stub_exe.o KCOV_INSTRUMENT := n -- 2.50.1