On Thu, Feb 04, 2016 at 08:45:35PM +0100, Denys Vlasenko wrote: > Sometimes gcc mysteriously doesn't inline > very small functions we expect to be inlined. See > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66122 > > With this .config: > http://busybox.net/~vda/kernel_config_OPTIMIZE_INLINING_and_Os, > the following functions get deinlined many times. > Examples of disassembly: > > <get_unaligned_be16> (12 copies, 51 calls): > 66 8b 07 mov (%rdi),%ax > 55 push %rbp > 48 89 e5 mov %rsp,%rbp > 86 e0 xchg %ah,%al > 5d pop %rbp > c3 retq > > <get_unaligned_be32> (12 copies, 135 calls): > 8b 07 mov (%rdi),%eax > 55 push %rbp > 48 89 e5 mov %rsp,%rbp > 0f c8 bswap %eax > 5d pop %rbp > c3 retq > > <get_unaligned_be64> (2 copies, 20 calls): > 48 8b 07 mov (%rdi),%rax > 55 push %rbp > 48 89 e5 mov %rsp,%rbp > 48 0f c8 bswap %rax > 5d pop %rbp > c3 retq > > <__swab16p> (16 copies, 146 calls): > 55 push %rbp > 89 f8 mov %edi,%eax > 86 e0 xchg %ah,%al > 48 89 e5 mov %rsp,%rbp > 5d pop %rbp > c3 retq > > <__swab32p> (43 copies, ~560 calls): > 55 push %rbp > 89 f8 mov %edi,%eax > 0f c8 bswap %eax > 48 89 e5 mov %rsp,%rbp > 5d pop %rbp > c3 retq > > <__swab64p> (21 copies, 119 calls): > 55 push %rbp > 48 89 f8 mov %rdi,%rax > 48 0f c8 bswap %rax > 48 89 e5 mov %rsp,%rbp > 5d pop %rbp > c3 retq > > <__swab32s> (6 copies, 47 calls): > 8b 07 mov (%rdi),%eax > 55 push %rbp > 48 89 e5 mov %rsp,%rbp > 0f c8 bswap %eax > 89 07 mov %eax,(%rdi) > 5d pop %rbp > c3 retq > > This patch fixes this via s/inline/__always_inline/. > Code size decrease after the patch is ~4.5k: > > text data bss dec hex filename > 92202377 20826112 36417536 149446025 8e85d89 vmlinux > 92197848 20826112 36417536 149441496 8e84bd8 vmlinux5_swap_after > > Signed-off-by: Denys Vlasenko <dvlas...@redhat.com> > Cc: Ingo Molnar <mi...@kernel.org> > Cc: Thomas Graf <tg...@suug.ch> > Cc: Peter Zijlstra <pet...@infradead.org> > Cc: David Rientjes <rient...@google.com> > Cc: Andrew Morton <a...@linux-foundation.org> > Cc: linux-kernel@vger.kernel.org > --- > include/uapi/linux/byteorder/big_endian.h | 24 ++++++++++++------------ > include/uapi/linux/byteorder/little_endian.h | 24 ++++++++++++------------ > include/uapi/linux/swab.h | 10 +++++----- > 3 files changed, 29 insertions(+), 29 deletions(-)
Hi, This patch seems to trigger a gcc bug which can produce corrupt code. I discovered it when investigating an objtool warning reported by kbuild bot: http://www.spinics.net/lists/linux-scsi/msg95481.html >From the disassembly of drivers/scsi/qla2xxx/qla_attr.o: 0000000000002f53 <qla2x00_get_host_fabric_name>: 2f53: 55 push %rbp 2f54: 48 89 e5 mov %rsp,%rbp 0000000000002f57 <qla2x00_get_fc_host_stats>: 2f57: 55 push %rbp 2f58: b9 e8 00 00 00 mov $0xe8,%ecx 2f5d: 48 89 e5 mov %rsp,%rbp ... Note that qla2x00_get_host_fabric_name() is inexplicably truncated after setting up the frame pointer. It falls through to the next function, which is very wrong. I can recreate it with either gcc 5.3.1 or gcc 6.0 on linus/master with the .config from the above link. The call chain which appears to trigger the problem is: qla2x00_get_host_fabric_name() wwn_to_u64() get_unaligned_be64() be64_to_cpup() __be64_to_cpup() <- changed to __always_inline by this patch It occurs with the combination of the following two recent commits: - bc27fb68aaad ("include/uapi/linux/byteorder, swab: force inlining of some byteswap operations") - ef3fb2422ffe ("scsi: fc: use get/put_unaligned64 for wwn access") I can confirm that reverting either patch makes the problem go away. I'm planning on opening a gcc bug tomorrow. > -static inline __u64 __be64_to_cpup(const __be64 *p) > +static __always_inline __u64 __be64_to_cpup(const __be64 *p) > { > return __swab64p((__u64 *)p); > } -- Josh
