BMC/Intel-BMC/linux.git/include/linux/compiler-gcc.h, branch dev-4.7

compiler.h: add support for malloc attribute

2016-05-20T02:12:14+00:00

gcc as far back as at least 3.04 documents the function attribute __malloc__. Add a shorthand for attaching that to a function declaration. This was also suggested by Andi Kleen way back in 2002 [1], but didn't get applied, perhaps because gcc at that time generated the exact same code with and without this attribute. This attribute tells the compiler that the return value (if non-NULL) can be assumed not to alias any other valid pointers at the time of the call. Please note that the documentation for a range of gcc versions (starting from around 4.7) contained a somewhat confusing and self-contradicting text: The malloc attribute is used to tell the compiler that a function may be treated as if any non-NULL pointer it returns cannot alias any other pointer valid when the function returns and *that the memory has undefined content*. [...] Standard functions with this property include malloc and *calloc*. (emphasis mine). The intended meaning has later been clarified [2]: This tells the compiler that a function is malloc-like, i.e., that the pointer P returned by the function cannot alias any other pointer valid when the function returns, and moreover no pointers to valid objects occur in any storage addressed by P. What this means is that we can apply the attribute to kmalloc and friends, and it is ok for the returned memory to have well-defined contents (__GFP_ZERO). But it is not ok to apply it to kmemdup(), nor to other functions which both allocate and possibly initialize the memory with existing pointers. So unless someone is doing something pretty perverted kstrdup() should also be a fine candidate. [1] http://thread.gmane.org/gmane.linux.kernel/57172 [2] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56955 Signed-off-by: Rasmus Villemoes Cc: Christoph Lameter Cc: Pekka Enberg Cc: David Rientjes Cc: Joonsoo Kim Cc: Andi Kleen Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

compiler-gcc: require gcc 4.8 for powerpc __builtin_bswap16()

2016-05-09T18:54:29+00:00

gcc support for __builtin_bswap16() was supposedly added for powerpc in gcc 4.6, and was then later added for other architectures in gcc 4.8. However, Stephen Rothwell reported that attempting to use it on powerpc in gcc 4.6 fails with: lib/vsprintf.c:160:2: error: initializer element is not constant lib/vsprintf.c:160:2: error: (near initialization for 'decpair[0]') lib/vsprintf.c:160:2: error: initializer element is not constant lib/vsprintf.c:160:2: error: (near initialization for 'decpair[1]') ... I'm not entirely sure what those errors mean, but I don't see them on gcc 4.8. So let's consider gcc 4.8 to be the official starting point for __builtin_bswap16(). Arnd Bergmann adds: "I found the commit in gcc-4.8 that replaced the powerpc-specific implementation of __builtin_bswap16 with an architecture-independent one. Apparently the powerpc version (gcc-4.6 and 4.7) just mapped to the lhbrx/sthbrx instructions, so it ended up not being a constant, though the intent of the patch was mainly to add support for the builtin to x86: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52624 has the patch that went into gcc-4.8 and more information." Fixes: 7322dd755e7d ("byteswap: try to avoid __builtin_constant_p gcc bug") Reported-by: Stephen Rothwell Tested-by: Stephen Rothwell Acked-by: Arnd Bergmann Signed-off-by: Josh Poimboeuf Signed-off-by: Stephen Rothwell Signed-off-by: Linus Torvalds

compiler-gcc: disable -ftracer for __noclone functions

2016-04-05T12:19:08+00:00

-ftracer can duplicate asm blocks causing compilation to fail in noclone functions. For example, KVM declares a global variable in an asm like asm("2: ... \n .pushsection data \n .global vmx_return \n vmx_return: .long 2b"); and -ftracer causes a double declaration. Cc: Andrew Morton Cc: Michal Marek Cc: stable@vger.kernel.org Cc: kvm@vger.kernel.org Reported-by: Linda Walsh Signed-off-by: Paolo Bonzini

include/linux/compiler-gcc.h: improve __visible documentation

2015-11-07T01:50:42+00:00

Cc: Andi Kleen Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

include/linux/compiler-gcc.h: hide assume_aligned attribute from sparse

2015-11-06T03:34:48+00:00

The patch "slab.h: sprinkle __assume_aligned attributes" causes *tons* of whinges if you do 'make C=2' with sparse 0.5.0: CHECK drivers/media/usb/pwc/pwc-if.c include/linux/slab.h:307:43: error: attribute '__assume_aligned__': unknown attribute include/linux/slab.h:308:58: error: attribute '__assume_aligned__': unknown attribute include/linux/slab.h:337:73: error: attribute '__assume_aligned__': unknown attribute include/linux/slab.h:375:74: error: attribute '__assume_aligned__': unknown attribute include/linux/slab.h:378:80: error: attribute '__assume_aligned__': unknown attribute sparse apparently pretends to be gcc >= 4.9, yet isn't prepared to handle all the function attributes supported by those gccs and complains loudly. So hide the definition of __assume_aligned from it (so that the generic one in compiler.h gets used). Signed-off-by: Rasmus Villemoes Reported-by: Valdis Kletnieks Tested-By: Valdis Kletnieks Cc: Christopher Li Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

compiler.h: add support for function attribute assume_aligned

2015-11-06T03:34:48+00:00

gcc 4.9 added the function attribute assume_aligned, indicating to the caller that the returned pointer may be assumed to have a certain minimal alignment. This is useful if, for example, the return value is passed to memset(). Add a shorthand macro for that. Signed-off-by: Rasmus Villemoes Cc: Christoph Lameter Cc: David Rientjes Cc: Pekka Enberg Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

compiler, atomics, kasan: Provide READ_ONCE_NOCHECK()

2015-10-20T09:04:19+00:00

Some code may perform racy by design memory reads. This could be harmless, yet such code may produce KASAN warnings. To hide such accesses from KASAN this patch introduces READ_ONCE_NOCHECK() macro. KASAN will not check the memory accessed by READ_ONCE_NOCHECK(). The KernelThreadSanitizer (KTSAN) is going to ignore it as well. This patch creates __read_once_size_nocheck() a clone of __read_once_size(). The only difference between them is 'no_sanitized_address' attribute appended to '*_nocheck' function. This attribute tells the compiler that instrumentation of memory accesses should not be applied to that function. We declare it as static '__maybe_unsed' because GCC is not capable to inline such function: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368 With KASAN=n READ_ONCE_NOCHECK() is just a clone of READ_ONCE(). Signed-off-by: Andrey Ryabinin Cc: Alexander Potapenko Cc: Andrew Morton Cc: Andrey Konovalov Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Denys Vlasenko Cc: Dmitry Vyukov Cc: Kostya Serebryany Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Sasha Levin Cc: Thomas Gleixner Cc: Wolfram Gloger Cc: kasan-dev Link: http://lkml.kernel.org/r/1445243838-17763-2-git-send-email-aryabinin@virtuozzo.com Signed-off-by: Ingo Molnar

compiler-gcc: integrate the various compiler-gcc[345].h files

2015-06-26T00:00:38+00:00

As gcc major version numbers are going to advance rather rapidly in the future, there's no real value in separate files for each compiler version. Deduplicate some of the macros #defined in each file too. Neaten comments using normal kernel commenting style. Signed-off-by: Joe Perches Cc: Andi Kleen Cc: Michal Marek Cc: Segher Boessenkool Cc: Sasha Levin Cc: Anton Blanchard Cc: Alan Modra Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

compiler-gcc.h: neatening

2015-06-26T00:00:37+00:00

- Move the inline and noinline blocks together - Comment neatening - Alignment of __attribute__ uses - Consistent naming of __must_be_array macro argument - Multiline macro neatening Signed-off-by: Joe Perches Cc: Andi Kleen Cc: Michal Marek Cc: Segher Boessenkool Cc: Sasha Levin Cc: Anton Blanchard Cc: Alan Modra Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

lib: make memzero_explicit more robust against dead store elimination

2015-05-04T09:49:51+00:00

In commit 0b053c951829 ("lib: memzero_explicit: use barrier instead of OPTIMIZER_HIDE_VAR"), we made memzero_explicit() more robust in case LTO would decide to inline memzero_explicit() and eventually find out it could be elimiated as dead store. While using barrier() works well for the case of gcc, recent efforts from LLVMLinux people suggest to use llvm as an alternative to gcc, and there, Stephan found in a simple stand-alone user space example that llvm could nevertheless optimize and thus elimitate the memset(). A similar issue has been observed in the referenced llvm bug report, which is regarded as not-a-bug. Based on some experiments, icc is a bit special on its own, while it doesn't seem to eliminate the memset(), it could do so with an own implementation, and then result in similar findings as with llvm. The fix in this patch now works for all three compilers (also tested with more aggressive optimization levels). Arguably, in the current kernel tree it's more of a theoretical issue, but imho, it's better to be pedantic about it. It's clearly visible with gcc/llvm though, with the below code: if we would have used barrier() only here, llvm would have omitted clearing, not so with barrier_data() variant: static inline void memzero_explicit(void *s, size_t count) { memset(s, 0, count); barrier_data(s); } int main(void) { char buff[20]; memzero_explicit(buff, sizeof(buff)); return 0; } $ gcc -O2 test.c $ gdb a.out (gdb) disassemble main Dump of assembler code for function main: 0x0000000000400400 <+0>: lea -0x28(%rsp),%rax 0x0000000000400405 <+5>: movq $0x0,-0x28(%rsp) 0x000000000040040e <+14>: movq $0x0,-0x20(%rsp) 0x0000000000400417 <+23>: movl $0x0,-0x18(%rsp) 0x000000000040041f <+31>: xor %eax,%eax 0x0000000000400421 <+33>: retq End of assembler dump. $ clang -O2 test.c $ gdb a.out (gdb) disassemble main Dump of assembler code for function main: 0x00000000004004f0 <+0>: xorps %xmm0,%xmm0 0x00000000004004f3 <+3>: movaps %xmm0,-0x18(%rsp) 0x00000000004004f8 <+8>: movl $0x0,-0x8(%rsp) 0x0000000000400500 <+16>: lea -0x18(%rsp),%rax 0x0000000000400505 <+21>: xor %eax,%eax 0x0000000000400507 <+23>: retq End of assembler dump. As gcc, clang, but also icc defines __GNUC__, it's sufficient to define this in compiler-gcc.h only to be picked up. For a fallback or otherwise unsupported compiler, we define it as a barrier. Similarly, for ecc which does not support gcc inline asm. Reference: https://llvm.org/bugs/show_bug.cgi?id=15495 Reported-by: Stephan Mueller Tested-by: Stephan Mueller Signed-off-by: Daniel Borkmann Cc: Theodore Ts'o Cc: Stephan Mueller Cc: Hannes Frederic Sowa Cc: mancha security Cc: Mark Charlebois Cc: Behan Webster Signed-off-by: Herbert Xu