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Re: PATCH: PR target/59672: Add -m16 support for x86
- From: Uros Bizjak <ubizjak at gmail dot com>
- To: "H.J. Lu" <hjl dot tools at gmail dot com>
- Cc: "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>, Jakub Jelinek <jakub at redhat dot com>, Richard Biener <rguenther at suse dot de>
- Date: Tue, 28 Jan 2014 17:30:20 +0100
- 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, Jan 28, 2014 at 5:01 PM, Uros Bizjak <ubizjak@gmail.com> 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.
>
> Please also add the entry to Changes.html, this is user-visible change.
Oh, a short scan-asm testcase would be nice, too.
Thanks,
Uros.