ply: Correct alignment of stack allocations

As entries are allocated on the stack the stack pointer is decremented
and then adjusted to meet the requested alignment requirements. The
current math does unfortunately not always provide the requested
alignment.

One example is when the stack pointer is at -1 and an allocation of 4
bytes with alignment of 4 is performed, which results in an allocation
at offset -6. A typical case where this happens is when working with
tracepoints containing boolean fields.

Update the adjustment to properly round the stack pointer down to the
requested alignment.

Signed-off-by: Bjorn Andersson <[email protected]>

src/libply/ir.c

@@ -520,7 +520,7 @@ ssize_t ir_alloc_stack(struct ir *ir, size_t size, size_t align)
 	ir->sp -= size;
 
 	if (ir->sp % align)
-		ir->sp -= align - (ir->sp & (align - 1));
+		ir->sp &= ~(align - 1);
 
 	assert(ir->sp > INT16_MIN);