linux/tools/objtool, branch v4.11

objtool: Fix another GCC jump table detection issue

2017-03-07T07:42:55Z

Arnd Bergmann reported a (false positive) objtool warning: drivers/infiniband/sw/rxe/rxe_resp.o: warning: objtool: rxe_responder()+0xfe: sibling call from callable instruction with changed frame pointer The issue is in find_switch_table(). It tries to find a switch statement's jump table by walking backwards from an indirect jump instruction, looking for a relocation to the .rodata section. In this case it stopped walking prematurely: the first .rodata relocation it encountered was for a variable (resp_state_name) instead of a jump table, so it just assumed there wasn't a jump table. The fix is to ignore any .rodata relocation which refers to an ELF object symbol. This works because the jump tables are anonymous and have no symbols associated with them. Reported-by: Arnd Bergmann Tested-by: Arnd Bergmann Signed-off-by: Josh Poimboeuf Cc: Denys Vlasenko Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: 3732710ff6f2 ("objtool: Improve rare switch jump table pattern detection") Link: http://lkml.kernel.org/r/20170302225723.3ndbsnl4hkqbne7a@treble Signed-off-by: Ingo Molnar

objtool, modules: Discard objtool annotation sections for modules

2017-03-01T19:32:25Z

The '__unreachable' and '__func_stack_frame_non_standard' sections are only used at compile time. They're discarded for vmlinux but they should also be discarded for modules. Since this is a recurring pattern, prefix the section names with ".discard.". It's a nice convention and vmlinux.lds.h already discards such sections. Also remove the 'a' (allocatable) flag from the __unreachable section since it doesn't make sense for a discarded section. Suggested-by: Linus Torvalds Signed-off-by: Josh Poimboeuf Cc: Jessica Yu Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: d1091c7fa3d5 ("objtool: Improve detection of BUG() and other dead ends") Link: http://lkml.kernel.org/r/20170301180444.lhd53c5tibc4ns77@treble Signed-off-by: Ingo Molnar

objtool: Improve detection of BUG() and other dead ends

2017-02-24T08:10:52Z

The BUG() macro's use of __builtin_unreachable() via the unreachable() macro tells gcc that the instruction is a dead end, and that it's safe to assume the current code path will not execute past the previous instruction. On x86, the BUG() macro is implemented with the 'ud2' instruction. When objtool's branch analysis sees that instruction, it knows the current code path has come to a dead end. Peter Zijlstra has been working on a patch to change the WARN macros to use 'ud2'. That patch will break objtool's assumption that 'ud2' is always a dead end. Generally it's best for objtool to avoid making those kinds of assumptions anyway. The more ignorant it is of kernel code internals, the better. So create a more generic way for objtool to detect dead ends by adding an annotation to the unreachable() macro. The annotation stores a pointer to the end of the unreachable code path in an '__unreachable' section. Objtool can read that section to find the dead ends. Tested-by: Peter Zijlstra (Intel) Signed-off-by: Josh Poimboeuf Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/41a6d33971462ebd944a1c60ad4bf5be86c17b77.1487712920.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar

objtool: Fix IRET's opcode

2017-01-19T07:39:44Z

The IRET opcode is 0xcf according to the Intel manual and also to objdump of my vmlinux: 1ea8: 48 cf iretq Fix the opcode in arch_decode_instruction(). The previous value (0xc5) seems to correspond to LDS. Signed-off-by: Jiri Slaby Acked-by: Josh Poimboeuf Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20170118132921.19319-1-jslaby@suse.cz Signed-off-by: Ingo Molnar

Merge branch 'kbuild' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild

2016-12-18T00:24:13Z

Pull kbuild updates from Michal Marek: - prototypes for x86 asm-exported symbols (Adam Borowski) and a warning about missing CRCs (Nick Piggin) - asm-exports fix for LTO (Nicolas Pitre) - thin archives improvements (Nick Piggin) - linker script fix for CONFIG_LD_DEAD_CODE_DATA_ELIMINATION (Nick Piggin) - genksyms support for __builtin_va_list keyword - misc minor fixes * 'kbuild' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild: x86/kbuild: enable modversions for symbols exported from asm kbuild: fix scripts/adjust_autoksyms.sh* for the no modules case scripts/kallsyms: remove last remnants of --page-offset option make use of make variable CURDIR instead of calling pwd kbuild: cmd_export_list: tighten the sed script kbuild: minor improvement for thin archives build kbuild: modpost warn if export version crc is missing kbuild: keep data tables through dead code elimination kbuild: improve linker compatibility with lib-ksyms.o build genksyms: Regenerate parser kbuild/genksyms: handle va_list type kbuild: thin archives for multi-y targets kbuild: kallsyms allow 3-pass generation if symbols size has changed

make use of make variable CURDIR instead of calling pwd

2016-12-11T11:12:56Z

make already provides the current working directory in a variable, so make use of it instead of forking a shell. Also replace usage of PWD by CURDIR. PWD is provided by most shells, but not all, so this makes the build system more robust. Signed-off-by: Uwe Kleine-König Signed-off-by: Michal Marek

objtool: Fix bytes check of lea's rex_prefix

2016-12-06T08:20:59Z

For the "lea %(rsp), %rbp" case, we check if there is a rex_prefix. But we check 'bytes' which is insn_byte_t[4] in rex_prefix (insn_field structure). Therefore, the check is always true. Instead, check 'nbytes' which is the right one. Signed-off-by: Jiri Slaby Acked-by: Josh Poimboeuf Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20161205105551.25917-1-jslaby@suse.cz Signed-off-by: Ingo Molnar

objtool: Fix rare switch jump table pattern detection

2016-10-27T06:20:27Z

The following commit: 3732710ff6f2 ("objtool: Improve rare switch jump table pattern detection") ... improved objtool's ability to detect GCC switch statement jump tables for GCC 6. However the check to allow short jumps with the scanned range of instructions wasn't quite right. The pattern detection should allow jumps to the indirect jump instruction itself. This fixes the following warning: drivers/infiniband/sw/rxe/rxe_comp.o: warning: objtool: rxe_completer()+0x315: sibling call from callable instruction with changed frame pointer Reported-by: Arnd Bergmann Signed-off-by: Josh Poimboeuf Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: 3732710ff6f2 ("objtool: Improve rare switch jump table pattern detection") Link: http://lkml.kernel.org/r/20161026153408.2rifnw7bvoc5sex7@treble Signed-off-by: Ingo Molnar

objtool: Skip all "unreachable instruction" warnings for gcov kernels

2016-10-16T07:12:36Z

Recently objtool has started reporting a few "unreachable instruction" warnings when CONFIG_GCOV is enabled for newer versions of GCC. Usually this warning means there's some new control flow that objtool doesn't understand. But in this case, objtool is correct and the instructions really are inaccessible. It's an annoying quirk of gcov, but it's harmless, so it's ok to just silence the warnings. With older versions of GCC, it was relatively easy to detect gcov-specific instructions and to skip any unreachable warnings produced by them. But GCC 6 has gotten craftier. Instead of continuing to play whack-a-mole with gcov, just use a bigger, more permanent hammer and disable unreachable warnings for the whole file when gcov is enabled. This is fine to do because a) unreachable warnings are usually of questionable value; and b) gcov isn't used for production kernels and we can relax the checks a bit there. Reported-by: kbuild test robot Signed-off-by: Josh Poimboeuf Cc: Andy Lutomirski Cc: Arnd Bergmann Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/38d5c87d61d9cd46486dd2c86f46603dff0df86f.1476393584.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar

objtool: Improve rare switch jump table pattern detection

2016-10-16T07:12:35Z

GCC 6 added a new switch statement jump table optimization which makes objtool's life harder. It looks like: mov [rodata addr],%reg1 ... some instructions ... jmpq *(%reg1,%reg2,8) The optimization is quite rare, but objtool still needs to be able to identify the pattern so that it can follow all possible control flow paths related to the switch statement. In order to detect the pattern, objtool starts from the indirect jump and scans backwards through the function until it finds the first instruction in the pattern. If it encounters an unconditional jump along the way, it stops and considers the pattern to be not found. As it turns out, unconditional jumps can happen, as long as they are small forward jumps within the range being scanned. This fixes the following warnings: drivers/infiniband/sw/rxe/rxe_comp.o: warning: objtool: rxe_completer()+0x2f4: sibling call from callable instruction with changed frame pointer drivers/infiniband/sw/rxe/rxe_resp.o: warning: objtool: rxe_responder()+0x10f: sibling call from callable instruction with changed frame pointer Reported-by: Arnd Bergmann Signed-off-by: Josh Poimboeuf Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/8a9ed68ae1780e8d3963e4ee13f2f257fe3a3c33.1476393584.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar