On Mon, May 17, 2021 at 01:39:46PM -0700, Nick Desaulniers wrote:

On Fri, May 14, 2021 at 1:54 PM Nathan Chancellor nathan@kernel.org wrote:

...

On 5/14/2021 11:12 AM, Naresh Kamboju wrote:

...

My two cents, We know clang-10 support is stopped, but our build system is still running

For the record, we are still building with clang-10 as that is the minimum supported version for the kernel.

...

these builds with clang-10. one of those observations is,

The LKFT build failures were noticed while building x86_64 and i386 with clang-10 on linux next-20210514 tag.

• x86_64 (defconfig) with clang-10 - FAIL
• i386 (defconfig) with clang-10 - FAIL
• x86_64 (defconfig) with clang-11 - PASS
• i386 (defconfig) with clang-11 - PASS
• x86_64 (defconfig) with clang-12 - PASS
• i386 (defconfig) with clang-12 - PASS

Build log:

make --silent --keep-going --jobs=8 O=/home/tuxbuild/.cache/tuxmake/builds/current ARCH=x86_64 CROSS_COMPILE=x86_64-linux-gnu- 'HOSTCC=sccache clang' 'CC=sccache clang'

drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool: eb_relocate_parse_slow()+0x427: stack state mismatch: cfa1=4+120 cfa2=-1+0 drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool: eb_copy_relocations()+0x1d5: stack state mismatch: cfa1=4+104 cfa2=-1+0 x86_64-linux-gnu-ld: arch/x86/kernel/kprobes/opt.o: in function `arch_prepare_optimized_kprobe': opt.c:(.text+0x798): undefined reference to `__compiletime_assert_251' make[1]: *** [/builds/linux/Makefile:1272: vmlinux] Error 1

Thanks for the report. Our CI also reported this:

https://github.com/ClangBuiltLinux/continuous-integration2/runs/2582534773?c...

My bisect landed on "mm, slub: change run-time assertion in kmalloc_index() to compile-time" in -next (I have added the author and reviewers to cc):

$ git bisect log # bad: [cd557f1c605fc5a2c0eb0b540610f50dc67dd849] Add linux-next specific files for 20210514 # good: [315d99318179b9cd5077ccc9f7f26a164c9fa998] Merge tag 'pm-5.13-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm git bisect start 'cd557f1c605fc5a2c0eb0b540610f50dc67dd849' '315d99318179b9cd5077ccc9f7f26a164c9fa998' # good: [9634d7cb3c506ae886a5136d12b4af696b9cee8a] Merge remote-tracking branch 'drm-misc/for-linux-next' git bisect good 9634d7cb3c506ae886a5136d12b4af696b9cee8a # good: [294636a24ae819a7caf0807d05d8eb5b964ec06f] Merge remote-tracking branch 'rcu/rcu/next' git bisect good 294636a24ae819a7caf0807d05d8eb5b964ec06f # good: [cb753d0611f912439c8e814f4254d15fa8fa1d75] Merge remote-tracking branch 'gpio-brgl/gpio/for-next' git bisect good cb753d0611f912439c8e814f4254d15fa8fa1d75 # bad: [b1e7389449084b74a044a70860c6a1c7466781cb] lib/string_helpers: switch to use BIT() macro git bisect bad b1e7389449084b74a044a70860c6a1c7466781cb # bad: [bf5570ed0654a21000e5dad9243ea1ba30bfe208] kasan: use dump_stack_lvl(KERN_ERR) to print stacks git bisect bad bf5570ed0654a21000e5dad9243ea1ba30bfe208 # bad: [4a292ff7a819404039588c7a9af272aca22c869e] fixup! mm: gup: pack has_pinned in MMF_HAS_PINNED git bisect bad 4a292ff7a819404039588c7a9af272aca22c869e # good: [93e440dd0e482b6cde20630d58016a451fb2b431] ocfs2: fix snprintf() checking git bisect good 93e440dd0e482b6cde20630d58016a451fb2b431 # good: [f32aeffdb407b6390ef17ccac87e1a1a76663354] slub: remove resiliency_test() function git bisect good f32aeffdb407b6390ef17ccac87e1a1a76663354 # bad: [2c9b936dae88dbdbb28666a741c87b08abb1b755] mm/page-writeback: update the comment of Dirty position control git bisect bad 2c9b936dae88dbdbb28666a741c87b08abb1b755 # bad: [597da4750c8e8f5f304419f3c66b713a88f3ebbe] tools/vm/page_owner_sort.c: check malloc() return git bisect bad 597da4750c8e8f5f304419f3c66b713a88f3ebbe # bad: [0ec3603432be3abba93ee7aa512cb6d83dd1c291] kfence: test: fix for "mm, slub: change run-time assertion in kmalloc_index() to compile-time" git bisect bad 0ec3603432be3abba93ee7aa512cb6d83dd1c291 # bad: [ff3daafe3fd3e54c8cf6aeb865099c7bb02e5c51] mm, slub: change run-time assertion in kmalloc_index() to compile-time git bisect bad ff3daafe3fd3e54c8cf6aeb865099c7bb02e5c51 # first bad commit: [ff3daafe3fd3e54c8cf6aeb865099c7bb02e5c51] mm, slub: change run-time assertion in kmalloc_index() to compile-time

https://git.kernel.org/next/linux-next/c/ff3daafe3fd3e54c8cf6aeb865099c7bb02...

It looks like LLVM fixed this in http://github.com/llvm/llvm-project/commit/6aabb109becfee37126ff7db3d41a41b5....

I think this happens because arch_prepare_optimized_kprobe() calls kzalloc() with a size of MAX_OPTINSN_SIZE, which is

#define MAX_OPTINSN_SIZE \ (((unsigned long)optprobe_template_end - \ (unsigned long)optprobe_template_entry) + \ MAX_OPTIMIZED_LENGTH + JMP32_INSN_SIZE)

and the optprobe_template_{end,entry} are not evaluated as constants.

I am not sure what the solution is. There seem to be a growing list of issues with LLVM 10 that were fixed in LLVM 11, which might necessitate requiring LLVM 11 and newer to build the kernel, given this affects a defconfig.

If we can make the compile time validation done instead at runtime for clang-10, that would be preferable. Then when we drop clang-10 support, we can revert that. Looking at the diff, I think we could reinstate parts like so:

diff --git a/include/linux/slab.h b/include/linux/slab.h index 9d316aac0aba..4c13e2cd415c 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -412,6 +412,9 @@ static __always_inline unsigned int __kmalloc_index(size_t size, if (size <= 8 * 1024 * 1024) return 23; if (size <= 16 * 1024 * 1024) return 24; if (size <= 32 * 1024 * 1024) return 25; +#if CLANG_VERSION <= 100000

•   if (size <=  64 * 1024 * 1024) return 26;
  

+#endif

    if (size_is_constant)
            BUILD_BUG_ON_MSG(1, "unexpected size in kmalloc_index()");

diff --git a/mm/slab_common.c b/mm/slab_common.c index a0b8ffeae4ae..ecb6104b9dbb 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -799,6 +799,9 @@ const struct kmalloc_info_struct kmalloc_info[] __initconst = { INIT_KMALLOC_INFO(8388608, 8M), INIT_KMALLOC_INFO(16777216, 16M), INIT_KMALLOC_INFO(33554432, 32M) +#if CLANG_VERSION <= 10000

•   ,INIT_KMALLOC_INFO(67108864, 64M)
  

+#endif };

/*

I adapted that patch as below but unfortunately, that did not resolve anything:

$ make -skj$(nproc) LLVM=1 LLVM_IAS=1 O=build/x86_64 distclean defconfig arch/x86/kernel/kprobes/opt.o

$ llvm-readelf -s build/x86_64/arch/x86/kernel/kprobes/opt.o | grep __compile 10: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND __compiletime_assert_251

I did suggest another change in the original patch thread:

https://lore.kernel.org/r/YKC9CeAfw3aBmHTU@archlinux-ax161/

Cheers, Nathan

--------------------------------------------------------

diff --git a/include/linux/slab.h b/include/linux/slab.h index 9d316aac0aba..c55c09544538 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -412,6 +412,9 @@ static __always_inline unsigned int __kmalloc_index(size_t size, if (size <= 8 * 1024 * 1024) return 23; if (size <= 16 * 1024 * 1024) return 24; if (size <= 32 * 1024 * 1024) return 25; +#if defined(CONFIG_CC_IS_CLANG) && CONFIG_CLANG_VERSION < 110000 + if (size <= 64 * 1024 * 1024) return 26; +#endif

if (size_is_constant) BUILD_BUG_ON_MSG(1, "unexpected size in kmalloc_index()"); diff --git a/mm/slab_common.c b/mm/slab_common.c index a0b8ffeae4ae..bd3fa2ed7e43 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -799,6 +799,9 @@ const struct kmalloc_info_struct kmalloc_info[] __initconst = { INIT_KMALLOC_INFO(8388608, 8M), INIT_KMALLOC_INFO(16777216, 16M), INIT_KMALLOC_INFO(33554432, 32M) +#if defined(CONFIG_CC_IS_CLANG) && CONFIG_CLANG_VERSION < 110000 + ,INIT_KMALLOC_INFO(67108864, 64M) +#endif };

/*