On Wed, Jan 29, 2014 at 1:52 AM, Richard Biener <rguent...@suse.de> wrote: > On Tue, 28 Jan 2014, Uros Bizjak wrote: > >> On Mon, Jan 27, 2014 at 8:44 PM, H.J. Lu <hongjiu...@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
Linux kernel people want it and clang has it. > addition of a --code16gcc assembler flag. Please make sure to > document the minimum required binutils to make this work. > Since the .code16gcc directive was added to binutils back in 1999, it is older than the minimum binutils required for x86 GCC. There is no need to specify a separate minimum binutils for it. -- H.J.
