Messages in this thread | | | Subject | Re: [PATCH 3/3] powerpc: use __builtin_trap() in BUG/WARN macros. | From | Christophe Leroy <> | Date | Mon, 19 Aug 2019 16:08:43 +0200 |
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Le 19/08/2019 à 15:23, Segher Boessenkool a écrit : > On Mon, Aug 19, 2019 at 01:06:31PM +0000, Christophe Leroy wrote: >> Note that we keep using an assembly text using "twi 31, 0, 0" for >> inconditional traps because GCC drops all code after >> __builtin_trap() when the condition is always true at build time. > > As I said, it can also do this for conditional traps, if it can prove > the condition is always true.
But we have another branch for 'always true' and 'always false' using __builtin_constant_p(), which don't use __builtin_trap(). Is there anything wrong with that ?:
#define BUG_ON(x) do { \ if (__builtin_constant_p(x)) { \ if (x) \ BUG(); \ } else { \ if (x) \ __builtin_trap(); \ BUG_ENTRY("", 0); \ } \ } while (0)
#define WARN_ON(x) ({ \ int __ret_warn_on = !!(x); \ if (__builtin_constant_p(__ret_warn_on)) { \ if (__ret_warn_on) \ __WARN_TAINT(TAINT_WARN); \ } else { \ if (__ret_warn_on) \ __builtin_trap(); \ BUG_ENTRY("", BUGFLAG_WARNING | BUGFLAG_TAINT(TAINT_WARN)); \ } \ unlikely(__ret_warn_on); \ })
> > Can you put the bug table asm *before* the __builtin_trap maybe? That > should make it all work fine... If you somehow can tell what machine > instruction is that trap, anyway.
And how can I tell that ?
When I put it *after*, it always points to the trap instruction. When I put it *before* it usually points on the first instruction used to prepare the registers for the trap condition.
Christophe
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