Messages in this thread | | | Date | Wed, 15 Jun 2016 16:55:16 +0000 (UTC) | From | Mathieu Desnoyers <> | Subject | stack validation warning on lttng-modules bytecode interpreter |
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Hi Josh,
I notice that with gcc 6.1.1, kernel 4.6, with CONFIG_STACK_VALIDATION=y, building lttng-modules master at commit 6c09dd94 gives this warning:
lttng-modules/lttng-filter-interpreter.o: warning: objtool: lttng_filter_interpret_bytecode()+0x58: sibling call from callable instruction with changed frame pointer
this object implements a bytecode interpreter using an explicit jump table (see https://github.com/lttng/lttng-modules/blob/master/lttng-filter-interpreter.c)
If I define "INTERPRETER_USE_SWITCH" at the top of the file, thus using the switch-case fallback implementation, the warning vanishes.
We use an explicit jump table rather than a switch case whenever possible for performance reasons.
I notice that tools/objtool/builtin-check.c needs to be aware of switch-cases transformed into jump tables by the compiler. Are explicit jump tables supported by the stack validator ? Do we need to add annotation to our code ?
Thanks,
Mathieu
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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