On 5/20/19 3:13 PM, Florian Weimer wrote:
> * Andrew Haley:
>
>> On 5/19/19 9:45 AM, Andrew Haley wrote:
>>> On 5/18/19 8:45 PM, Hamad Ahmed wrote:
>>>> How do I do that?
>>>
>>> Seriously? Go find the ABI for your processor and find out which
>>> registers are call clobbered. Write a subroutine in assembly language
>>> that zeroes those registers.
>>
>> And actually, you can go one better than that: write a bunch of inline asms
>> that zero all of the registers, one at a time.
>>
>> #define CLOBBER(reg) \
>> asm volatile("sub %%" #reg ", %%" #reg ::: #reg, "memory")
>>
>> static inline void foo() {
>> CLOBBER(rax);
>> CLOBBER(rbx);
>> CLOBBER(rcx);
>> CLOBBER(rdx);
>> CLOBBER(rbp);
>> CLOBBER(rax);
>> CLOBBER(rsi);
>> CLOBBER(rdi);
>> CLOBBER(r8);
>> CLOBBER(r9);
>> CLOBBER(r10);
>> CLOBBER(r11);
>> CLOBBER(r12);
>> CLOBBER(r13);
>> CLOBBER(r14);
>> CLOBBER(r15);
>> }
>>
>> This will mostly work, I think, but even then it's not 100% guaranteed.
>
> With most ABIs, there's also an issue with callee-saved registers, which
> could leave dead pointers on the stack (because the callee will save the
> register even if it is dead in the caller).
True.
> The above kludge does not clear those pointers, obviously.
Yep. There are no guarantees.
--
Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
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