Hi, 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. --- gcc/ChangeLog.m16 | 16 ++++++++++++++++ gcc/config/i386/gnu-user64.h | 6 +++--- gcc/config/i386/i386.c | 6 ++++++ gcc/config/i386/i386.h | 2 ++ gcc/config/i386/i386.opt | 6 +++++- gcc/doc/invoke.texi | 10 ++++++++-- 6 files changed, 40 insertions(+), 6 deletions(-) create mode 100644 gcc/ChangeLog.m16 diff --git a/gcc/ChangeLog.m16 b/gcc/ChangeLog.m16 new file mode 100644 index 0000000..05424d9 --- /dev/null +++ b/gcc/ChangeLog.m16 @@ -0,0 +1,16 @@ +gcc/ + +2014-01-23 H.J. Lu <hongjiu...@intel.com> + + 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. diff --git a/gcc/config/i386/gnu-user64.h b/gcc/config/i386/gnu-user64.h index 8d33483..1c72b41 100644 --- a/gcc/config/i386/gnu-user64.h +++ b/gcc/config/i386/gnu-user64.h @@ -32,12 +32,12 @@ see the files COPYING3 and COPYING.RUNTIME respectively. If not, see done. */ #if TARGET_64BIT_DEFAULT -#define SPEC_32 "m32" +#define SPEC_32 "m16|m32" #if TARGET_BI_ARCH == 2 #define SPEC_64 "m64" -#define SPEC_X32 "m32|m64:;" +#define SPEC_X32 "m16|m32|m64:;" #else -#define SPEC_64 "m32|mx32:;" +#define SPEC_64 "m16|m32|mx32:;" #define SPEC_X32 "mx32" #endif #else diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c index cf79486..c132cd9 100644 --- a/gcc/config/i386/i386.c +++ b/gcc/config/i386/i386.c @@ -3342,6 +3342,10 @@ ix86_option_override_internal (bool main_args_p, opts->x_ix86_isa_flags |= OPTION_MASK_ISA_64BIT; opts->x_ix86_isa_flags &= ~OPTION_MASK_ABI_64; } + else if (TARGET_16BIT_P (opts->x_ix86_isa_flags)) + opts->x_ix86_isa_flags &= ~(OPTION_MASK_ISA_64BIT + | OPTION_MASK_ABI_X32 + | OPTION_MASK_ABI_64); else if (TARGET_LP64_P (opts->x_ix86_isa_flags)) { /* Always turn on OPTION_MASK_ISA_64BIT and turn off @@ -38815,6 +38819,8 @@ static void x86_file_start (void) { default_file_start (); + if (TARGET_16BIT) + fputs ("\t.code16gcc\n", asm_out_file); #if TARGET_MACHO darwin_file_start (); #endif diff --git a/gcc/config/i386/i386.h b/gcc/config/i386/i386.h index 580a319..bfb6dc6 100644 --- a/gcc/config/i386/i386.h +++ b/gcc/config/i386/i386.h @@ -135,6 +135,8 @@ see the files COPYING3 and COPYING.RUNTIME respectively. If not, see #define TARGET_LP64_P(x) TARGET_ABI_64_P(x) #define TARGET_X32 TARGET_ABI_X32 #define TARGET_X32_P(x) TARGET_ABI_X32_P(x) +#define TARGET_16BIT TARGET_CODE16 +#define TARGET_16BIT_P(x) TARGET_CODE16_P(x) /* SSE4.1 defines round instructions */ #define OPTION_MASK_ISA_ROUND OPTION_MASK_ISA_SSE4_1 diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt index 26cd8bb..485ed2a 100644 --- a/gcc/config/i386/i386.opt +++ b/gcc/config/i386/i386.opt @@ -558,9 +558,13 @@ Target RejectNegative Negative(mx32) Report Mask(ABI_64) Var(ix86_isa_flags) Sav Generate 64bit x86-64 code mx32 -Target RejectNegative Negative(m32) Report Mask(ABI_X32) Var(ix86_isa_flags) Save +Target RejectNegative Negative(m16) Report Mask(ABI_X32) Var(ix86_isa_flags) Save Generate 32bit x86-64 code +m16 +Target RejectNegative Negative(m32) Report Mask(CODE16) InverseMask(ISA_64BIT) Var(ix86_isa_flags) Save +Generate 16bit i386 code + mmmx Target Report Mask(ISA_MMX) Var(ix86_isa_flags) Save Support MMX built-in functions diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi index 8c620a5..c87f08b 100644 --- a/gcc/doc/invoke.texi +++ b/gcc/doc/invoke.texi @@ -680,7 +680,7 @@ Objective-C and Objective-C++ Dialects}. -mpc32 -mpc64 -mpc80 -mstackrealign @gol -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol -mcmodel=@var{code-model} -mabi=@var{name} -maddress-mode=@var{mode} @gol --m32 -m64 -mx32 -mlarge-data-threshold=@var{num} @gol +-m32 -m64 -mx32 -m16 -mlarge-data-threshold=@var{num} @gol -msse2avx -mfentry -m8bit-idiv @gol -mavx256-split-unaligned-load -mavx256-split-unaligned-store @gol -mstack-protector-guard=@var{guard}} @@ -15635,10 +15635,12 @@ on x86-64 processors in 64-bit environments. @item -m32 @itemx -m64 @itemx -mx32 +@itemx -m16 @opindex m32 @opindex m64 @opindex mx32 -Generate code for a 32-bit or 64-bit environment. +@opindex m16 +Generate code for a 16-bit, 32-bit or 64-bit environment. The @option{-m32} option sets @code{int}, @code{long}, and pointer types to 32 bits, and generates code that runs on any i386 system. @@ -15652,6 +15654,10 @@ The @option{-mx32} option sets @code{int}, @code{long}, and pointer types to 32 bits, and generates code for the x86-64 architecture. +The @option{-m16} option is the same as @option{-m32}, except for that +it outputs the @code{.code16gcc} assembly directive at the beginning of +the assembly output so that the binary can run in 16-bit mode. + @item -mno-red-zone @opindex mno-red-zone Do not use a so-called ``red zone'' for x86-64 code. The red zone is mandated -- 1.8.5.3