Messages in this thread | | | Date | Wed, 18 Mar 2020 19:00:04 -0700 | From | Nathan Chancellor <> | Subject | Re: [PATCH v2] tracing: Use address-of operator on section symbols |
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On Wed, Feb 19, 2020 at 10:10:12PM -0700, Nathan Chancellor wrote: > Clang warns: > > ../kernel/trace/trace.c:9335:33: warning: array comparison always > evaluates to true [-Wtautological-compare] > if (__stop___trace_bprintk_fmt != __start___trace_bprintk_fmt) > ^ > 1 warning generated. > > These are not true arrays, they are linker defined symbols, which are > just addresses. Using the address of operator silences the warning and > does not change the runtime result of the check (tested with some print > statements compiled in with clang + ld.lld and gcc + ld.bfd in QEMU). > > Link: https://github.com/ClangBuiltLinux/linux/issues/893 > Suggested-by: Nick Desaulniers <ndesaulniers@google.com> > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> > --- > > v1 -> v2: https://lore.kernel.org/lkml/20200219045423.54190-4-natechancellor@gmail.com/ > > * No longer a series because there is no prerequisite patch. > * Use address-of operator instead of casting to unsigned long. > > NOTE: The code generation does seem to change, unlike every other call > site that I did this change to but the result of the check remains the > same as noted in the commit message and I cannot really understand what > has changed in the assembly. Please let me know if there is something > catastrophically wrong. > > kernel/trace/trace.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index c797a15a1fc7..78727dd9a6f5 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -9332,7 +9332,7 @@ __init static int tracer_alloc_buffers(void) > goto out_free_buffer_mask; > > /* Only allocate trace_printk buffers if a trace_printk exists */ > - if (__stop___trace_bprintk_fmt != __start___trace_bprintk_fmt) > + if (&__stop___trace_bprintk_fmt != &__start___trace_bprintk_fmt) > /* Must be called before global_trace.buffer is allocated */ > trace_printk_init_buffers(); > > -- > 2.25.1 >
Gentle ping for review/acceptance.
Cheers, Nathan
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