On Tue, Nov 26, 2013 at 12:30 PM, Ilya Enkovich <enkovich....@gmail.com> wrote: >>>> CM_MEDIUM has unlimited data size. >>>>> >>>>> i386-opts.h: CM_MEDIUM, /* Assumes code fits in the low 31 >>>>> bits; data unlimited. */ >>>>> >>>>> The x86_64_zext_immediate_operand allows _address_ to be loaded by >>>>> movl. The @SIZE reloc returns object size, which is unlimited and has >>>>> no connection to its address. For CM_MEDIUM, >>>>> x86_64_zext_immediate_operand allows: >>>>> >>>>> return (ix86_cmodel == CM_SMALL >>>>> || (ix86_cmodel == CM_MEDIUM >>>>> && !SYMBOL_REF_FAR_ADDR_P (op))); >>>> >>>> Yes, but large symbols never have SYMBOL_FLAG_FAR_ADDR set. >>> >>> Sorry, I mean all large symbols have this flag set. >> >> This flag marks the fact that object size is bigger than >> -mlarge-data-threshold and goes into large section. It is true that >> UInt option argument currently overflows at 4G, and consequently all >> sizes larger than 4G go to large sections, but IMO, we should not rely >> on this. The specification says unlimited data size, so we have to be >> prepared for this. >> >> The reason I am against checking "Z" constraint is that "@SIZE" >> relocation returns _size_ of the object (which is only remotely >> connected to its address), while "Z" checks the address of the object. >> So, it looks to me that this check would be conceptually wrong. >> >> The right place to "fix" movabs is in a linker relaxation pass that >> can check the real size and change movabs to movl if the size fits >> 32bits. >> >> As a side note, perhaps generic option subsystem should reject >> overflows as e.g. -mlarge-data-threshold=5368709120 when 32bit UInt is >> used for option argument. The effects of overflow are surprising. > > Hi Uros, > > Thanks for explanations! I'll make a fix for the patch. > > BTW Pointer Bounds Checker feature does not go to 4.9 and therefore > this size relocation instructions is not required in 4.9. Suppose it > should go into 4.10 because doubt this feature is useful for anyone > except me. > > This also affects all MPX instructions. With no checker in 4.9, no one > actually uses them. Please tell me if I should pull them back from > trunk.
The instructions in *.md are usually well isolated, so I'd suggest to remove them. Since all issues in this part ware resolved, they could be added back without problems. BR, Uros.
