SUBALIGN does not Appear to Work

[RetroRevivalGames]

Hi Bebbo. Since #29 I've gotten a ROM image for the SEGA Mega Drive to build and run successfully.

I've come across one more minor issue. I'm using -ffunction-sections and -fdata-sections along with --gc-sections to reduce ROM size. It works nicely but the linker seems to force a 4-byte alignment between each input section. In other words, each function/variable now has a few 0 bytes to align the next function/variable on a 4-byte boundary, which can chew up some space for larger programs. I'm trying to align on a 2-byte boundary.

Same lds. I've tried different values for the .text section's SUBALIGN command (0, 1, 2, 3, 4) and each time it aligns on a 4-byte boundary.

ENTRY(__START)

MEMORY
{
    rom (rx)  : ORIGIN = 0x00000000, LENGTH = 0x00400000
    ram (rwx) : ORIGIN = 0x00FF0000, LENGTH = 0x00010000
}

SECTIONS
{
    .text 0x00000000 : SUBALIGN(2) {
        KEEP(*(.header))
        *(.boot)
        *(.main)
        *(.text*)
        *(.vdp)
        *(.rodata .rodata.*)
    } > rom
    __stext = SIZEOF(.text);

    .data 0x00FF0000 : AT( ADDR(.text) + SIZEOF(.text) ) {
        *(.data*)
        *(.asmdata)
        FILL(0x00)
        . = ALIGN(2);
    } > ram
    __sdata = SIZEOF(.data);

    .bss 0x00FF0000 + SIZEOF(.data) : {
        *(.bss) 
    } > ram
}

Not sure how much it would take to remedy this but if it's not too much of a hassle it'd be awesome if this was implemented.

I've done a little research into it. Looks like asection struct has align_power variable. Not sure if that could be used to allow users to configure the input section alignments via SUBALIGN?

[bebbo]

the assembler already aligns everything at 4 byte boundaries:

START:
  rts

->

00000000 00000000 START:
   0:   4e75            rts
   2:   0000    .short 0x0000

[bebbo]

and it's hard coded atm:

newsect->alignment_power = 2;

[bebbo]

And last but not least: the Amiga hunk file format supports only multiples of 4. => this won't work using Amiga hunks.

workarounds:

• use a different target
• use function/data sections only to figure what gets used, then attribute (with conditional defines) these with special named sections. All wanted stuff ends up in these named sections.

[RetroRevivalGames]

Makes sense. I figured hunk would have that alignment limitation.

As far as using a different target, this toolchain only supports hunk correct? I remember trying to compile amiga-gcc with TARGET=m68k-elf and it failed.

[bebbo]

Makes sense. I figured hunk would have that alignment limitation.

As far as using a different target, this toolchain only supports hunk correct? I remember trying to compile amiga-gcc with TARGET=m68k-elf and it failed.

a) why aren't you using a stock m68k-elf? b) make TARGET=m68k-elf gcc should work, but other stuff fails...

[RetroRevivalGames]

a) why aren't you using a stock m68k-elf?

Stack heavy / slower assembly generated

b) make TARGET=m68k-elf gcc should work, but other stuff fails...

Unfortunately this is failing at binutils gas. Looks like some functions aren't getting proper parameters.

[bebbo]

try again in 30 mins

[bebbo]

make binutils -j30 TARGET=m68k-elf make binutils bfd... make binutils bfd...done make binutils gas... make binutils gas...done make binutils binutils... make binutils binutils...done make binutils ld... make binutils ld...done install binutils... install binutils...done

[RetroRevivalGames]

OK. Building only binutils does work. I was building all of gcc using make gcc TARGET=m68k-elf

[bebbo]

gcc should compile too, but not newlib

[RetroRevivalGames]

Tried it again. Yes, looks like it built correctly. Tried it out and it works perfectly. Exactly what I was looking for, the high efficiency of your assembly generation with the elf binary format. I even got lto plugins to work with small modifications to the Makefile in amiga-gcc. Just remove --disable-plugins from binutils configuration.

Thank you Bebbo.

[bebbo]

Tried it again. Yes, looks like it built correctly. Tried it out and it works perfectly. Exactly what I was looking for, the high efficiency of your assembly generation with the elf binary format. I even got lto plugins to work with small modifications to the Makefile in amiga-gcc. Just remove --disable-plugins from binutils configuration.

Thank you Bebbo.

I will omit --disable-plugins if target is m68k-elf.