Integrated: 8289046: Undefined Behaviour in x86 class Assembler

[Andrew Haley]

On Thu, 23 Jun 2022 14:52:54 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);

This pull request has now been integrated.

Changeset: 86ef7b20
Author:    Andrew Haley <aph at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/86ef7b20eb45899a91cf9ee83f723336c9477694
Stats:     114 lines in 7 files changed: 65 ins; 9 del; 40 mod

8289046: Undefined Behaviour in x86 class Assembler

Reviewed-by: shade, kvn

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