kernel/linux.git/include/linux/compiler-gcc.h, branch v6.12.80

unreachable: Unify

2025-03-07T17:25:35+00:00

[ Upstream commit c837de3810982cd41cd70e5170da1931439f025c ] Since barrier_before_unreachable() is empty for !GCC it is trivial to unify the two definitions. Less is more. Signed-off-by: Peter Zijlstra (Intel) Acked-by: Josh Poimboeuf Link: https://lore.kernel.org/r/20241128094311.924381359@infradead.org Stable-dep-of: 73cfc53cc3b6 ("objtool: Fix C jump table annotations for Clang") Signed-off-by: Sasha Levin

kasan: Fix Software Tag-Based KASAN with GCC

2024-10-23T15:04:30+00:00

Per [1], -fsanitize=kernel-hwaddress with GCC currently does not disable instrumentation in functions with __attribute__((no_sanitize_address)). However, __attribute__((no_sanitize("hwaddress"))) does correctly disable instrumentation. Use it instead. Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117196 [1] Link: https://lore.kernel.org/r/000000000000f362e80620e27859@google.com Link: https://lore.kernel.org/r/ZvFGwKfoC4yVjN_X@J2N7QTR9R3 Link: https://bugzilla.kernel.org/show_bug.cgi?id=218854 Reported-by: syzbot+908886656a02769af987@syzkaller.appspotmail.com Tested-by: Andrey Konovalov Cc: Andrew Pinski Cc: Mark Rutland Cc: Will Deacon Signed-off-by: Marco Elver Reviewed-by: Andrey Konovalov Fixes: 7b861a53e46b ("kasan: Bump required compiler version") Link: https://lore.kernel.org/r/20241021120013.3209481-1-elver@google.com Signed-off-by: Will Deacon

init/Kconfig: remove CONFIG_GCC_ASM_GOTO_OUTPUT_WORKAROUND

2024-07-18T17:33:14+00:00

Several versions of GCC mis-compile asm goto with outputs. We try to workaround this, but our workaround is demonstrably incomplete and liable to result in subtle bugs, especially on arm64 where get_user() has recently been moved over to using asm goto with outputs. From discussion(s) with Linus at: https://lore.kernel.org/linux-arm-kernel/Zpfv2tnlQ-gOLGac@J2N7QTR9R3.cambridge.arm.com/ https://lore.kernel.org/linux-arm-kernel/ZpfxLrJAOF2YNqCk@J2N7QTR9R3.cambridge.arm.com/ ... it sounds like the best thing to do for now is to remove the workaround and make CC_HAS_ASM_GOTO_OUTPUT depend on working compiler versions. The issue was originally reported to GCC by Sean Christopherson: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113921 ... and Jakub Jelinek fixed this for GCC 14, with the fix backported to 13.3.0, 12.4.0, and 11.5.0. In the kernel, we tried to workaround broken compilers in commits: 4356e9f841f7 ("work around gcc bugs with 'asm goto' with outputs") 68fb3ca0e408 ("update workarounds for gcc "asm goto" issue") ... but the workaround of adding an empty asm("") after the asm volatile goto(...) demonstrably does not always avoid the problem, as can be seen in the following test case: | #define asm_goto_output(x...) \ | do { asm volatile goto(x); asm (""); } while (0) | | #define __good_or_bad(__val, __key) \ | do { \ | __label__ __failed; \ | unsigned long __tmp; \ | asm_goto_output( \ | " cbnz %[key], %l[__failed]\n" \ | " mov %[val], #0x900d\n" \ | : [val] "=r" (__tmp) \ | : [key] "r" (__key) \ | : \ | : __failed); \ | (__val) = __tmp; \ | break; \ | __failed: \ | (__val) = 0xbad; \ | } while (0) | | unsigned long get_val(unsigned long key); | unsigned long get_val(unsigned long key) | { | unsigned long val = 0xbad; | | __good_or_bad(val, key); | | return val; | } GCC 13.2.0 (at -O2) compiles this to: | cbnz x0, .Lfailed | mov x0, #0x900d | .Lfailed: | ret GCC 14.1.0 (at -O2) compiles this to: | cbnz x0, .Lfailed | mov x0, #0x900d | ret | .Lfailed: | mov x0, #0xbad | ret Note that GCC 13.2.0 erroneously omits the assignment to 'val' in the error path (even though this does not depend on an output of the asm goto). GCC 14.1.0 correctly retains the assignment. This problem can be seen within the kernel with the following test case: | #include | #include | | noinline unsigned long test_unsafe_get_user(unsigned long __user *ptr); | noinline unsigned long test_unsafe_get_user(unsigned long __user *ptr) | { | unsigned long val; | | unsafe_get_user(val, ptr, Efault); | return val; | | Efault: | val = 0x900d; | return val; | } GCC 13.2.0 (arm64 defconfig) compiles this to: | and x0, x0, #0xff7fffffffffffff | ldtr x0, [x0] | .Lextable_fixup: | ret GCC 13.2.0 (x86_64 defconfig + MITIGATION_RETPOLINE=n) compiles this to: | endbr64 | mov (%rdi),%rax | .Lextable_fixup: | ret ... omitting the assignment to 'val' in the error path, and leaving garbage in the result register returned by the function (which happens to contain the faulting address in the generated code). GCC 14.1.0 (arm64 defconfig) compiles this to: | and x0, x0, #0xff7fffffffffffff | ldtr x0, [x0] | ret | .Lextable_fixup: | mov x0, #0x900d // #36877 | ret GCC 14.1.0 (x86_64 defconfig + MITIGATION_RETPOLINE=n) compiles this to: | endbr64 | mov (%rdi),%rax | ret | .Lextable_fixup: | mov $0x900d,%eax | ret ... retaining the expected assignment to 'val' in the error path. We don't have a complete and reasonable workaround. While placing empty asm("") blocks after each goto label *might* be sufficient, we don't know for certain, this is tedious and error-prone, and there doesn't seem to be a neat way to wrap this up (which is especially painful for cases with multiple goto labels). Avoid this issue by disabling CONFIG_CC_HAS_ASM_GOTO_OUTPUT for known-broken compiler versions and removing the workaround (along with the CONFIG_GCC_ASM_GOTO_OUTPUT_WORKAROUND config option). For the moment I've left the default implementation of asm_goto_output() unchanged. This should now be redundant since any compiler with the fix for the clobbering issue whould also have a fix for the (earlier) volatile issue, but it's far less churny to leave it around, which makes it easier to backport this patch if necessary. Signed-off-by: Mark Rutland Cc: Alex Coplan Cc: Catalin Marinas Cc: Jakub Jelinek Cc: Peter Zijlstra Cc: Sean Christopherson Cc: Szabolcs Nagy Cc: Will Deacon Cc: linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Linus Torvalds

Merge tag 'x86-core-2024-03-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2024-03-12T02:53:15+00:00

Pull core x86 updates from Ingo Molnar: - The biggest change is the rework of the percpu code, to support the 'Named Address Spaces' GCC feature, by Uros Bizjak: - This allows C code to access GS and FS segment relative memory via variables declared with such attributes, which allows the compiler to better optimize those accesses than the previous inline assembly code. - The series also includes a number of micro-optimizations for various percpu access methods, plus a number of cleanups of %gs accesses in assembly code. - These changes have been exposed to linux-next testing for the last ~5 months, with no known regressions in this area. - Fix/clean up __switch_to()'s broken but accidentally working handling of FPU switching - which also generates better code - Propagate more RIP-relative addressing in assembly code, to generate slightly better code - Rework the CPU mitigations Kconfig space to be less idiosyncratic, to make it easier for distros to follow & maintain these options - Rework the x86 idle code to cure RCU violations and to clean up the logic - Clean up the vDSO Makefile logic - Misc cleanups and fixes * tag 'x86-core-2024-03-11' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (52 commits) x86/idle: Select idle routine only once x86/idle: Let prefer_mwait_c1_over_halt() return bool x86/idle: Cleanup idle_setup() x86/idle: Clean up idle selection x86/idle: Sanitize X86_BUG_AMD_E400 handling sched/idle: Conditionally handle tick broadcast in default_idle_call() x86: Increase brk randomness entropy for 64-bit systems x86/vdso: Move vDSO to mmap region x86/vdso/kbuild: Group non-standard build attributes and primary object file rules together x86/vdso: Fix rethunk patching for vdso-image-{32,64}.o x86/retpoline: Ensure default return thunk isn't used at runtime x86/vdso: Use CONFIG_COMPAT_32 to specify vdso32 x86/vdso: Use $(addprefix ) instead of $(foreach ) x86/vdso: Simplify obj-y addition x86/vdso: Consolidate targets and clean-files x86/bugs: Rename CONFIG_RETHUNK => CONFIG_MITIGATION_RETHUNK x86/bugs: Rename CONFIG_CPU_SRSO => CONFIG_MITIGATION_SRSO x86/bugs: Rename CONFIG_CPU_IBRS_ENTRY => CONFIG_MITIGATION_IBRS_ENTRY x86/bugs: Rename CONFIG_CPU_UNRET_ENTRY => CONFIG_MITIGATION_UNRET_ENTRY x86/bugs: Rename CONFIG_SLS => CONFIG_MITIGATION_SLS ...

update workarounds for gcc "asm goto" issue

2024-02-15T19:14:33+00:00

In commit 4356e9f841f7 ("work around gcc bugs with 'asm goto' with outputs") I did the gcc workaround unconditionally, because the cause of the bad code generation wasn't entirely clear. In the meantime, Jakub Jelinek debugged the issue, and has come up with a fix in gcc [2], which also got backported to the still maintained branches of gcc-11, gcc-12 and gcc-13. Note that while the fix technically wasn't in the original gcc-14 branch, Jakub says: "while it is true that no GCC 14 snapshots until today (or whenever the fix will be committed) have the fix, for GCC trunk it is up to the distros to use the latest snapshot if they use it at all and would allow better testing of the kernel code without the workaround, so that if there are other issues they won't be discovered years later. Most userland code doesn't actually use asm goto with outputs..." so we will consider gcc-14 to be fixed - if somebody is using gcc snapshots of the gcc-14 before the fix, they should upgrade. Note that while the bug goes back to gcc-11, in practice other gcc changes seem to have effectively hidden it since gcc-12.1 as per a bisect by Jakub. So even a gcc-14 snapshot without the fix likely doesn't show actual problems. Also, make the default 'asm_goto_output()' macro mark the asm as volatile by hand, because of an unrelated gcc issue [1] where it doesn't match the documented behavior ("asm goto is always volatile"). Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103979 [1] Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113921 [2] Link: https://lore.kernel.org/all/20240208220604.140859-1-seanjc@google.com/ Requested-by: Jakub Jelinek Cc: Uros Bizjak Cc: Nick Desaulniers Cc: Sean Christopherson Cc: Andrew Pinski Signed-off-by: Linus Torvalds

Merge branch 'x86/bugs' into x86/core, to pick up pending changes before dependent patches

2024-02-14T09:49:37+00:00

Merge in pending alternatives patching infrastructure changes, before applying more patches. Signed-off-by: Ingo Molnar

work around gcc bugs with 'asm goto' with outputs

2024-02-09T23:57:48+00:00

We've had issues with gcc and 'asm goto' before, and we created a 'asm_volatile_goto()' macro for that in the past: see commits 3f0116c3238a ("compiler/gcc4: Add quirk for 'asm goto' miscompilation bug") and a9f180345f53 ("compiler/gcc4: Make quirk for asm_volatile_goto() unconditional"). Then, much later, we ended up removing the workaround in commit 43c249ea0b1e ("compiler-gcc.h: remove ancient workaround for gcc PR 58670") because we no longer supported building the kernel with the affected gcc versions, but we left the macro uses around. Now, Sean Christopherson reports a new version of a very similar problem, which is fixed by re-applying that ancient workaround. But the problem in question is limited to only the 'asm goto with outputs' cases, so instead of re-introducing the old workaround as-is, let's rename and limit the workaround to just that much less common case. It looks like there are at least two separate issues that all hit in this area: (a) some versions of gcc don't mark the asm goto as 'volatile' when it has outputs: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98619 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110420 which is easy to work around by just adding the 'volatile' by hand. (b) Internal compiler errors: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110422 which are worked around by adding the extra empty 'asm' as a barrier, as in the original workaround. but the problem Sean sees may be a third thing since it involves bad code generation (not an ICE) even with the manually added 'volatile'. but the same old workaround works for this case, even if this feels a bit like voodoo programming and may only be hiding the issue. Reported-and-tested-by: Sean Christopherson Link: https://lore.kernel.org/all/20240208220604.140859-1-seanjc@google.com/ Cc: Nick Desaulniers Cc: Uros Bizjak Cc: Jakub Jelinek Cc: Andrew Pinski Signed-off-by: Linus Torvalds

x86/bugs: Rename CONFIG_RETPOLINE => CONFIG_MITIGATION_RETPOLINE

2024-01-10T09:52:28+00:00

Step 5/10 of the namespace unification of CPU mitigations related Kconfig options. [ mingo: Converted a few more uses in comments/messages as well. ] Suggested-by: Josh Poimboeuf Signed-off-by: Breno Leitao Signed-off-by: Ingo Molnar Reviewed-by: Ariel Miculas Acked-by: Josh Poimboeuf Cc: Linus Torvalds Link: https://lore.kernel.org/r/20231121160740.1249350-6-leitao@debian.org

compiler-gcc: Suppress -Wmissing-prototypes warning for all supported GCC

2023-11-10T15:53:19+00:00

The kernel supports a minimum GCC version of 5.1.0 for building. However, the "__diag_ignore_all" directive only suppresses the "-Wmissing-prototypes" warning for GCC versions >= 8.0.0. As a result, when building the kernel with older GCC versions, warnings may be triggered. The example below illustrates the warnings reported by the kernel test robot using GCC 7.5.0: compiler: gcc-7 (Ubuntu 7.5.0-6ubuntu2) 7.5.0 All warnings (new ones prefixed by >>): kernel/bpf/helpers.c:1893:19: warning: no previous prototype for 'bpf_obj_new_impl' [-Wmissing-prototypes] __bpf_kfunc void *bpf_obj_new_impl(u64 local_type_id__k, void *meta__ign) ^~~~~~~~~~~~~~~~ kernel/bpf/helpers.c:1907:19: warning: no previous prototype for 'bpf_percpu_obj_new_impl' [-Wmissing-prototypes] __bpf_kfunc void *bpf_percpu_obj_new_impl(u64 local_type_id__k, void *meta__ign) [...] To address this, we should also suppress the "-Wmissing-prototypes" warning for older GCC versions. "#pragma GCC diagnostic push" is supported as of GCC 4.6, and both "-Wmissing-prototypes" and "-Wmissing-declarations" are supported for all the GCC versions that we currently support. Therefore, it is reasonable to suppress these warnings for all supported GCC versions. With this adjustment, it's important to note that after implementing "__diag_ignore_all", it will effectively suppress warnings for all the supported GCC versions. In the future, if you wish to suppress warnings that are only supported on higher GCC versions, it is advisable to explicitly use "__diag_ignore" to specify the GCC version you are targeting. Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-kbuild-all/202311031651.A7crZEur-lkp@intel.com/ Suggested-by: Arnd Bergmann Signed-off-by: Yafang Shao Cc: Kumar Kartikeya Dwivedi Cc: Arnd Bergmann Acked-by: Arnd Bergmann Link: https://lore.kernel.org/r/20231106031802.4188-1-laoar.shao@gmail.com Signed-off-by: Alexei Starovoitov

compiler.h: unify __UNIQUE_ID

2023-10-04T17:41:56+00:00

commit 6f33d58794ef ("__UNIQUE_ID()") added a fallback definition of __UNIQUE_ID because gcc 4.2 and older did not support __COUNTER__. Also, this commit is effectively a revert of commit b41c29b0527c ("Kbuild: provide a __UNIQUE_ID for clang") which mentions clang 2.6+ supporting __COUNTER__. Documentation/process/changes.rst currently lists the minimum supported version of these compilers as: - gcc: 5.1 - clang: 11.0.0 It should be safe to say that __COUNTER__ is well supported by this point. Link: https://lkml.kernel.org/r/20230831-unique_id-v1-1-28bacd18eb1d@google.com Signed-off-by: Nick Desaulniers Cc: Arnd Bergmann Cc: Jan Beulich Cc: Luc Van Oostenryck Cc: Michal rarek Cc: Nathan Chancellor Cc: Paul Russel Cc: Tom Rix Signed-off-by: Andrew Morton