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![Uros Bizjak](/assets/img/avatar_default.png)
The workaround for 'asm goto' miscompilation introduces a compiler barrier quirk that inhibits many useful compiler optimizations. For example, __try_cmpxchg_user compiles to: 11375: 41 8b 4d 00 mov 0x0(%r13),%ecx 11379: 41 8b 02 mov (%r10),%eax 1137c: f0 0f b1 0a lock cmpxchg %ecx,(%rdx) 11380: 0f 94 c2 sete %dl 11383: 84 d2 test %dl,%dl 11385: 75 c4 jne 1134b <...> 11387: 41 89 02 mov %eax,(%r10) where the barrier inhibits flags propagation from asm when compiled with gcc-12. When the mentioned quirk is removed, the following code is generated: 11553: 41 8b 4d 00 mov 0x0(%r13),%ecx 11557: 41 8b 02 mov (%r10),%eax 1155a: f0 0f b1 0a lock cmpxchg %ecx,(%rdx) 1155e: 74 c9 je 11529 <...> 11560: 41 89 02 mov %eax,(%r10) The refered compiler bug: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670 was fixed for gcc-4.8.2. Current minimum required version of GCC is version 5.1 which has the above 'asm goto' miscompilation fixed, so remove the workaround. Link: https://lkml.kernel.org/r/20220624141412.72274-1-ubizjak@gmail.com Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
148 lines
4.2 KiB
C
148 lines
4.2 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef __LINUX_COMPILER_TYPES_H
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#error "Please don't include <linux/compiler-gcc.h> directly, include <linux/compiler.h> instead."
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#endif
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/*
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* Common definitions for all gcc versions go here.
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*/
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#define GCC_VERSION (__GNUC__ * 10000 \
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+ __GNUC_MINOR__ * 100 \
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+ __GNUC_PATCHLEVEL__)
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/*
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* This macro obfuscates arithmetic on a variable address so that gcc
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* shouldn't recognize the original var, and make assumptions about it.
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*
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* This is needed because the C standard makes it undefined to do
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* pointer arithmetic on "objects" outside their boundaries and the
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* gcc optimizers assume this is the case. In particular they
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* assume such arithmetic does not wrap.
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*
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* A miscompilation has been observed because of this on PPC.
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* To work around it we hide the relationship of the pointer and the object
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* using this macro.
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*
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* Versions of the ppc64 compiler before 4.1 had a bug where use of
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* RELOC_HIDE could trash r30. The bug can be worked around by changing
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* the inline assembly constraint from =g to =r, in this particular
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* case either is valid.
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*/
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#define RELOC_HIDE(ptr, off) \
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({ \
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unsigned long __ptr; \
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__asm__ ("" : "=r"(__ptr) : "0"(ptr)); \
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(typeof(ptr)) (__ptr + (off)); \
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})
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#ifdef CONFIG_RETPOLINE
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#define __noretpoline __attribute__((__indirect_branch__("keep")))
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#endif
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#define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)
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#if defined(LATENT_ENTROPY_PLUGIN) && !defined(__CHECKER__)
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#define __latent_entropy __attribute__((latent_entropy))
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#endif
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/*
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* calling noreturn functions, __builtin_unreachable() and __builtin_trap()
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* confuse the stack allocation in gcc, leading to overly large stack
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* frames, see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82365
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*
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* Adding an empty inline assembly before it works around the problem
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*/
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#define barrier_before_unreachable() asm volatile("")
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/*
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* Mark a position in code as unreachable. This can be used to
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* suppress control flow warnings after asm blocks that transfer
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* control elsewhere.
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*/
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#define unreachable() \
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do { \
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annotate_unreachable(); \
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barrier_before_unreachable(); \
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__builtin_unreachable(); \
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} while (0)
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#if defined(CONFIG_ARCH_USE_BUILTIN_BSWAP)
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#define __HAVE_BUILTIN_BSWAP32__
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#define __HAVE_BUILTIN_BSWAP64__
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#define __HAVE_BUILTIN_BSWAP16__
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#endif /* CONFIG_ARCH_USE_BUILTIN_BSWAP */
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#if GCC_VERSION >= 70000
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#define KASAN_ABI_VERSION 5
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#else
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#define KASAN_ABI_VERSION 4
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#endif
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#ifdef CONFIG_SHADOW_CALL_STACK
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#define __noscs __attribute__((__no_sanitize__("shadow-call-stack")))
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#endif
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#if __has_attribute(__no_sanitize_address__)
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#define __no_sanitize_address __attribute__((no_sanitize_address))
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#else
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#define __no_sanitize_address
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#endif
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#if defined(__SANITIZE_THREAD__) && __has_attribute(__no_sanitize_thread__)
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#define __no_sanitize_thread __attribute__((no_sanitize_thread))
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#else
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#define __no_sanitize_thread
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#endif
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#if __has_attribute(__no_sanitize_undefined__)
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#define __no_sanitize_undefined __attribute__((no_sanitize_undefined))
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#else
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#define __no_sanitize_undefined
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#endif
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#if defined(CONFIG_KCOV) && __has_attribute(__no_sanitize_coverage__)
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#define __no_sanitize_coverage __attribute__((no_sanitize_coverage))
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#else
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#define __no_sanitize_coverage
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#endif
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/*
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* Treat __SANITIZE_HWADDRESS__ the same as __SANITIZE_ADDRESS__ in the kernel,
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* matching the defines used by Clang.
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*/
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#ifdef __SANITIZE_HWADDRESS__
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#define __SANITIZE_ADDRESS__
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#endif
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/*
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* Turn individual warnings and errors on and off locally, depending
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* on version.
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*/
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#define __diag_GCC(version, severity, s) \
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__diag_GCC_ ## version(__diag_GCC_ ## severity s)
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/* Severity used in pragma directives */
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#define __diag_GCC_ignore ignored
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#define __diag_GCC_warn warning
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#define __diag_GCC_error error
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#define __diag_str1(s) #s
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#define __diag_str(s) __diag_str1(s)
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#define __diag(s) _Pragma(__diag_str(GCC diagnostic s))
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#if GCC_VERSION >= 80000
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#define __diag_GCC_8(s) __diag(s)
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#else
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#define __diag_GCC_8(s)
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#endif
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#define __diag_ignore_all(option, comment) \
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__diag_GCC(8, ignore, option)
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/*
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* Prior to 9.1, -Wno-alloc-size-larger-than (and therefore the "alloc_size"
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* attribute) do not work, and must be disabled.
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*/
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#if GCC_VERSION < 90100
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#undef __alloc_size__
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#endif
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