Messages in this thread | | | Date | Mon, 22 Oct 2018 11:22:55 +0100 | From | Will Deacon <> | Subject | Re: [tip:locking/core 6/10] arch/x86/include/asm/rmwcc.h:23:17: error: jump into statement expression |
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On Mon, Oct 22, 2018 at 12:08:30PM +0200, Peter Zijlstra wrote: > ARGH; so, this: > > #define __GEN_RMWcc(fullop, _var, cc, clobbers, ...) \ > ({ \ > bool c = false; \ > asm_volatile_goto (fullop "; j" #cc " %l[cc_label]" \ > : : [var] "m" (_var), ## __VA_ARGS__ \ > : clobbers : cc_label); \ > if (0) { \ > cc_label: c = true; \ > } \ > c; \ > }) > > static __always_inline u32 queued_fetch_set_pending_acquire(struct qspinlock *lock) > { > u32 val = 0; > > if (GEN_BINARY_RMWcc(LOCK_PREFIX "btsl", lock->val.counter, c, > "I", _Q_PENDING_OFFSET)) > val |= _Q_PENDING_VAL; > > val |= atomic_read(&lock->val) & ~_Q_PENDING_MASK; > > return val; > } > > fails to compile when combined with this: > > #define if(cond, ...) __trace_if( (cond , ## __VA_ARGS__) )
Rosteeeedt!
> #define __trace_if(cond) \ > if (__builtin_constant_p(!!(cond)) ? !!(cond) : \ > ({ \ > int ______r; \ > static struct ftrace_branch_data \ > __attribute__((__aligned__(4))) \ > __attribute__((section("_ftrace_branch"))) \ > ______f = { \ > .func = __func__, \ > .file = __FILE__, \ > .line = __LINE__, \ > }; \ > ______r = !!(cond); \ > ______f.miss_hit[______r]++; \ > ______r; \ > })) > > Because that moves the __GEN_RMWcc into a statement expression and GCC > apparently doesn't like labels inside statement expressions. > > If we avoid if() and rewrite queued_fetch_set_pending_acquire() like so: > > static __always_inline u32 queued_fetch_set_pending_acquire(struct qspinlock *lock) > { > bool pending; > u32 val; > > pending = GEN_BINARY_RMWcc(LOCK_PREFIX "btsl", lock->val.counter, c, > "I", _Q_PENDING_OFFSET); > > val = pending * _Q_PENDING_VAL; > val |= atomic_read(&lock->val) & ~_Q_PENDING_MASK; > > return val; > } > > then it compiles again; but urgh. > > Anybody see a better solution?
No, that looks about right to me, but please throw in a comment so that we don't "fix" this in the future.
Will
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