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Fix build errors due to CONFIG_BRANCH_TRACER=y
The code that enables branch tracing for all (non-constant) branches
plays games with the preprocessor and #define's the C 'if ()' construct
to do tracing.
That's all fine, but it fails for some unusual but valid C code that is
sometimes used in macros, notably by the intel-iommu code:
if (i=drhd->iommu, drhd->ignored) ..
because now the preprocessor complains about multiple arguments to the
'if' macro.
So make the macro expansion of this particularly horrid trick use
varargs, and handle the case of comma-expressions in if-statements. Use
another macro to do it cleanly in just one place.
This replaces a patch by David (and acked by Steven) that did this all
inside that one already-too-horrid macro.
Tested-by: Ingo Molnar <mingo@elte.hu>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>