path: root/Makefile
diff options
authorLinus Torvalds <>2016-03-20 18:23:21 -0700
committerLinus Torvalds <>2016-03-20 18:23:21 -0700
commit26660a4046b171a752e72a1dd32153230234fe3a (patch)
tree1389db3db2130e1082250fa0ab1e8684f7e31f39 /Makefile
parent46e595a17dcf11404f713845ecb5b06b92a94e43 (diff)
parent1bcb58a099938c33acda78b212ed67b06b3359ef (diff)
Merge branch 'core-objtool-for-linus' of git://
Pull 'objtool' stack frame validation from Ingo Molnar: "This tree adds a new kernel build-time object file validation feature (ONFIG_STACK_VALIDATION=y): kernel stack frame correctness validation. It was written by and is maintained by Josh Poimboeuf. The motivation: there's a category of hard to find kernel bugs, most of them in assembly code (but also occasionally in C code), that degrades the quality of kernel stack dumps/backtraces. These bugs are hard to detect at the source code level. Such bugs result in incorrect/incomplete backtraces most of time - but can also in some rare cases result in crashes or other undefined behavior. The build time correctness checking is done via the new 'objtool' user-space utility that was written for this purpose and which is hosted in the kernel repository in tools/objtool/. The tool's (very simple) UI and source code design is shaped after Git and perf and shares quite a bit of infrastructure with tools/perf (which tooling infrastructure sharing effort got merged via perf and is already upstream). Objtool follows the well-known kernel coding style. Objtool does not try to check .c or .S files, it instead analyzes the resulting .o generated machine code from first principles: it decodes the instruction stream and interprets it. (Right now objtool supports the x86-64 architecture.) From tools/objtool/Documentation/stack-validation.txt: "The kernel CONFIG_STACK_VALIDATION option enables a host tool named objtool which runs at compile time. It has a "check" subcommand which analyzes every .o file and ensures the validity of its stack metadata. It enforces a set of rules on asm code and C inline assembly code so that stack traces can be reliable. Currently it only checks frame pointer usage, but there are plans to add CFI validation for C files and CFI generation for asm files. For each function, it recursively follows all possible code paths and validates the correct frame pointer state at each instruction. It also follows code paths involving special sections, like .altinstructions, __jump_table, and __ex_table, which can add alternative execution paths to a given instruction (or set of instructions). Similarly, it knows how to follow switch statements, for which gcc sometimes uses jump tables." When this new kernel option is enabled (it's disabled by default), the tool, if it finds any suspicious assembly code pattern, outputs warnings in compiler warning format: warning: objtool: rtlwifi_rate_mapping()+0x2e7: frame pointer state mismatch warning: objtool: cik_tiling_mode_table_init()+0x6ce: call without frame pointer save/setup warning: objtool:__schedule()+0x3c0: duplicate frame pointer save warning: objtool:__schedule()+0x3fd: sibling call from callable instruction with changed frame pointer ... so that scripts that pick up compiler warnings will notice them. All known warnings triggered by the tool are fixed by the tree, most of the commits in fact prepare the kernel to be warning-free. Most of them are bugfixes or cleanups that stand on their own, but there are also some annotations of 'special' stack frames for justified cases such entries to JIT-ed code (BPF) or really special boot time code. There are two other long-term motivations behind this tool as well: - To improve the quality and reliability of kernel stack frames, so that they can be used for optimized live patching. - To create independent infrastructure to check the correctness of CFI stack frames at build time. CFI debuginfo is notoriously unreliable and we cannot use it in the kernel as-is without extra checking done both on the kernel side and on the build side. The quality of kernel stack frames matters to debuggability as well, so IMO we can merge this without having to consider the live patching or CFI debuginfo angle" * 'core-objtool-for-linus' of git:// (52 commits) objtool: Only print one warning per function objtool: Add several performance improvements tools: Copy hashtable.h into tools directory objtool: Fix false positive warnings for functions with multiple switch statements objtool: Rename some variables and functions objtool: Remove superflous INIT_LIST_HEAD objtool: Add helper macros for traversing instructions objtool: Fix false positive warnings related to sibling calls objtool: Compile with debugging symbols objtool: Detect infinite recursion objtool: Prevent infinite recursion in noreturn detection objtool: Detect and warn if libelf is missing and don't break the build tools: Support relative directory path for 'O=' objtool: Support CROSS_COMPILE x86/asm/decoder: Use explicitly signed chars objtool: Enable stack metadata validation on 64-bit x86 objtool: Add CONFIG_STACK_VALIDATION option objtool: Add tool to perform compile-time stack metadata validation x86/kprobes: Mark kretprobe_trampoline() stack frame as non-standard sched: Always inline context_switch() ...
Diffstat (limited to 'Makefile')
1 files changed, 17 insertions, 3 deletions
diff --git a/Makefile b/Makefile
index 6798c6b4775d..e055b969c325 100644
--- a/Makefile
+++ b/Makefile
@@ -993,7 +993,21 @@ prepare0: archprepare FORCE
$(Q)$(MAKE) $(build)=.
# All the preparing..
-prepare: prepare0
+prepare: prepare0 prepare-objtool
+ has_libelf := $(shell echo "int main() {}" | $(HOSTCC) -xc -o /dev/null -lelf - &> /dev/null && echo 1 || echo 0)
+ ifeq ($(has_libelf),1)
+ objtool_target := tools/objtool FORCE
+ else
+ $(warning "Cannot use CONFIG_STACK_VALIDATION, please install libelf-dev or elfutils-libelf-devel")
+ endif
+PHONY += prepare-objtool
+prepare-objtool: $(objtool_target)
# Generate some files
# ---------------------------------------------------------------------------
@@ -1516,11 +1530,11 @@ image_name:
# Clear a bunch of variables before executing the submake
tools/: FORCE
$(Q)mkdir -p $(objtree)/tools
- $(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(filter --j% -j,$(MAKEFLAGS))" O=$(O) subdir=tools -C $(src)/tools/
+ $(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(filter --j% -j,$(MAKEFLAGS))" O=$(shell cd $(objtree) && /bin/pwd) subdir=tools -C $(src)/tools/
tools/%: FORCE
$(Q)mkdir -p $(objtree)/tools
- $(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(filter --j% -j,$(MAKEFLAGS))" O=$(O) subdir=tools -C $(src)/tools/ $*
+ $(Q)$(MAKE) LDFLAGS= MAKEFLAGS="$(filter --j% -j,$(MAKEFLAGS))" O=$(shell cd $(objtree) && /bin/pwd) subdir=tools -C $(src)/tools/ $*
# Single targets
# ---------------------------------------------------------------------------