RFR: 8289046: Undefined Behaviour in x86 class Assembler [v5]

[Aleksey Shipilev]

On Tue, 5 Jul 2022 08:12:23 GMT, Andrew Haley <aph at openjdk.org> wrote:

>> All instances of type Register exhibit UB in the form of wild pointer (including null pointer) dereferences. This isn't very hard to fix: we should make Registers pointers to something rather than aliases of small integers. 
>> 
>> Here's an example of what was happening:
>> 
>>    ` rax->encoding();`
>> 
>> Where rax is defined as `(Register *)0`.
>> 
>> This patch things so that rax is now defined as a pointer to the start of a static array of RegisterImpl.
>> 
>> 
>> typedef const RegisterImpl* Register;
>> extern RegisterImpl all_Registers[RegisterImpl::number_of_declared_registers + 1] ;
>> inline constexpr Register RegisterImpl::first() { return all_Registers + 1; };
>> inline constexpr Register as_Register(int encoding) { return RegisterImpl::first() + encoding; }
>> constexpr Register rax = as_register(0);
>
> Andrew Haley has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Delete changes to hotspot/shared.

Looks okay to me, with minor nits.

src/hotspot/cpu/x86/register_x86.cpp line 47:

> 45:     KRegisterImpl::max_slots_per_register * KRegisterImpl::number_of_registers;
> 46: 
> 47: const char * RegisterImpl::name() const {

Suggestion:

const char* RegisterImpl::name() const {

src/hotspot/cpu/x86/register_x86.hpp line 170:

> 168:   int raw_encoding() const                       { return this - first(); }
> 169:   int   encoding() const                         { assert(is_valid(), "invalid register"); return raw_encoding(); }
> 170:   bool  is_valid() const                          { return 0 <= raw_encoding() && raw_encoding() < number_of_registers; }

Suggestion:

  bool  is_valid() const                         { return 0 <= raw_encoding() && raw_encoding() < number_of_registers; }

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Marked as reviewed by shade (Reviewer).

PR: https://git.openjdk.org/jdk/pull/9261