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Re: PATCH: PR target/59672: Add -m16 support for x86
- From: Richard Biener <rguenther at suse dot de>
- To: Uros Bizjak <ubizjak at gmail dot com>
- Cc: "H.J. Lu" <hjl dot tools at gmail dot com>, "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>, Jakub Jelinek <jakub at redhat dot com>
- Date: Wed, 29 Jan 2014 10:52:00 +0100 (CET)
- Subject: Re: PATCH: PR target/59672: Add -m16 support for x86
- Authentication-results: sourceware.org; auth=none
- References: <20140127194457 dot GA12183 at intel dot com> <CAFULd4YBgcMtNVX8_7yYJ_7NStPu+g0axqhBJLeUTazfwRTnSA at mail dot gmail dot com>
On Tue, 28 Jan 2014, Uros Bizjak wrote:
> On Mon, Jan 27, 2014 at 8:44 PM, H.J. Lu <hongjiu.lu@intel.com> wrote:
>
> > The .code16gcc directive was added to binutils back in 1999:
> >
> > ---
> > '.code16gcc' provides experimental support for generating 16-bit code
> > from gcc, and differs from '.code16' in that 'call', 'ret', 'enter',
> > 'leave', 'push', 'pop', 'pusha', 'popa', 'pushf', and 'popf'
> > instructions default to 32-bit size. This is so that the stack pointer
> > is manipulated in the same way over function calls, allowing access to
> > function parameters at the same stack offsets as in 32-bit mode.
> > '.code16gcc' also automatically adds address size prefixes where
> > necessary to use the 32-bit addressing modes that gcc generates.
> > ---
> >
> > It encodes 32-bit assembly instructions generated by GCC in 16-bit format
> > so that GCC can be used to generate 16-bit instructions. To do that, the
> > .code16gcc directive may be placed at the very beginning of the assembly
> > code. This patch adds -m16 to x86 backend by:
> >
> > 1. Add -m16 and make it mutually exclusive with -m32, -m64 and -mx32.
> > 2. Treat -m16 like -m32 so that --32 is passed to assembler.
> > 3. Output .code16gcc at the very beginning of the assembly code.
> > 4. Turn off 64-bit ISA when -m16 is used.
> >
> > Tested on Linux/x86 and Linux/x86-64. OK for trunk?
> >
> > Thanks.
> >
> > H.J.
> > ---
> > PR target/59672
> > * config/i386/gnu-user64.h (SPEC_32): Add "m16|" to "m32".
> > (SPEC_X32): Likewise.
> > (SPEC_64): Likewise.
> > * config/i386/i386.c (ix86_option_override_internal): Turn off
> > OPTION_MASK_ISA_64BIT, OPTION_MASK_ABI_X32 and OPTION_MASK_ABI_64
> > for TARGET_16BIT.
> > (x86_file_start): Output .code16gcc for TARGET_16BIT.
> > * config/i386/i386.h (TARGET_16BIT): New macro.
> > (TARGET_16BIT_P): Likewise.
> > * config/i386/i386.opt: Add m16.
> > * doc/invoke.texi: Document -m16.
>
> OK for mainline, needs OK from RMs for a backport.
I don't think this is suitable for the branch. Unless there is
tremendous need for it somewhere ...? I like the suggested
addition of a --code16gcc assembler flag. Please make sure to
document the minimum required binutils to make this work.
Richard.