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Subject: [PING][PATCH] increase stack and malloc alignment to 16 bytes
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Precedence: bulk

Pinging another patch that I think is important, particularly for -msse users.

Note that gcc / libstdc++ also expect 16-byte alignment, as evidenced by
alignof(std::max_align_t) == 16, the macro __STDCPP_DEFAULT_NEW_ALIGNMENT__
(defined to 16), and the fact that it always bumps the stack pointer by
multiples of 16.


On 2021-11-25 16:13, J.W. Jagersma wrote:
> The section alignment patch I posted here earlier has been accepted in binutils,
> so that will be available in the next release.
> 
> Now in libc only these two lines need to be adjusted, and then all code, data,
> stack and heap will be aligned to 16 byte boundaries.
> 
> Should be good for SSE, hopefully it will help resolve the gcc 11 Ada issue too.
> 
> ---
>  src/libc/ansi/stdlib/nmalcdef.h | 2 +-
>  src/libc/crt0/crt0.S            | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/src/libc/ansi/stdlib/nmalcdef.h b/src/libc/ansi/stdlib/nmalcdef.h
> index cb41f619..495c63a6 100644
> --- a/src/libc/ansi/stdlib/nmalcdef.h
> +++ b/src/libc/ansi/stdlib/nmalcdef.h
> @@ -188,7 +188,7 @@ typedef struct memblock {
>  /* conversion and access macros */
>  #define MEMBLKp(p) (memblockp)((byte*)(p) - DATAOFFSET)
>  #define PTR(m)     (void*)((byte*)(m) + DATAOFFSET)
> -#define ALIGN 8
> +#define ALIGN 16
>  
>  #define ALIGNMASK (ALIGN-1)
>  
> diff --git a/src/libc/crt0/crt0.S b/src/libc/crt0/crt0.S
> index 446a989b..226f0cb9 100644
> --- a/src/libc/crt0/crt0.S
> +++ b/src/libc/crt0/crt0.S
> @@ -315,7 +315,7 @@ use_stubinfo_stack_size:
>  	addl	__stklen, %eax
>  	movw	%ds, %dx		/* set stack */
>  	movw	%dx, %ss
> -	andb	$0xf8, %al		/* align to 8-byte boundary */
> +	andb	$0xf0, %al		/* align to 16-byte boundary */
>  	movl	%eax, %esp
>  	movl	%eax, ___djgpp_stack_top	/* Top of stack */
>  	subl	___djgpp_stack_limit, %eax