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devkitProのgccはリンカスクリプトを通してプログラムの配置を決定しています。ファイルは「C:\devkitPro\devkitARM\arm-none-eabi\lib」の「gba_cart.ld」 、マルチブート用は「gba_mb.ld」になります。短いので全文を以下に記載します。わけわからないと思いますが、ある程度は読んでみてください。全ては理解できないものの一部は馴染みのある記載をしています。
/* Linker Script Original v1.3 by Jeff Frohwein */
/* v1.0 - Original release */
/* v1.1 - Added proper .data section support */
/* v1.2 - Added support for c++ & iwram overlays */
/* - Major contributions by Jason Wilkins. */
/* v1.3 - .ewram section now can be used when */
/* compiling for MULTIBOOT mode. This fixes */
/* malloc() in DevKitAdvance which depends */
/* on __eheap_start instead of end to define*/
/* the starting location of heap space. */
/* External global variable __gba_iwram_heap*/
/* support added to allow labels end, _end, */
/* & __end__ to point to end of iwram or */
/* the end of ewram. */
/* Additions by WinterMute */
/* v1.4 - .sbss section added for unitialised */
/* data in ewram */
/* v1.5 - padding section added to stop EZF */
/* stripping important data */
/* This file is released into the public domain */
/* for commercial or non-commercial use with no */
/* restrictions placed upon it. */
/* NOTE!!!: This linker script defines the RAM & */
/* ROM start addresses. In order for it to work */
/* properly, remove -Ttext and -Tbss linker */
/* options from your makefile if they are */
/* present. */
/* You can use the following to view section */
/* addresses in your .elf file: */
/* objdump -h file.elf */
/* Please note that empty sections may incorrectly*/
/* list the lma address as the vma address for */
/* some versions of objdump. */
OUTPUT_FORMAT("elf32-littlearm", "elf32-bigarm", "elf32-littlearm")
OUTPUT_ARCH(arm)
ENTRY(_start)
/* SEARCH_DIR(/bin/arm); */
/* The linker script function "var1 += var2;" sometimes */
/* reports incorrect values in the *.map file but the */
/* actual value it calculates is usually, if not always, */
/* correct. If you leave out the ". = ALIGN(4);" at the */
/* end of each section then the return value of SIZEOF() */
/* is sometimes incorrect and "var1 += var2;" appears to */
/* not work as well. "var1 += var2" style functions are */
/* avoided below as a result. */
MEMORY {
rom : ORIGIN = 0x08000000, LENGTH = 32M
iwram : ORIGIN = 0x03000000, LENGTH = 32K
ewram : ORIGIN = 0x02000000, LENGTH = 256K
}
__text_start = ORIGIN(rom);
__eheap_end = ORIGIN(ewram) + LENGTH(ewram);
__iwram_start = ORIGIN(iwram);
__iwram_top = ORIGIN(iwram) + LENGTH(iwram);;
__sp_irq = __iwram_top - 0x060;
__sp_usr = __sp_irq - 0x0a0;
__irq_flags = 0x03007ff8;
SECTIONS
{
. = __text_start;
.crt0 :
{
KEEP (*(.crt0))
. = ALIGN(4);
} >rom =0xff
.init :
{
KEEP (*(SORT_NONE(.init)))
} >rom
.plt :
{
*(.plt)
. = ALIGN(4); /* REQUIRED. LD is flaky without it. */
} >rom
.text : /* ALIGN (4): */
{
*(EXCLUDE_FILE (*.iwram*) .text*)
*(.gnu.linkonce.t.*)
KEEP (*(.text.*personality*))
/* .gnu.warning sections are handled specially by elf32.em. */
*(.gnu.warning)
*(.glue_7t) *(.glue_7) *(.vfp11_veneer)
. = ALIGN(4); /* REQUIRED. LD is flaky without it. */
} >rom = 0xff
__text_end = .;
.fini :
{
KEEP (*(.fini))
. = ALIGN(4); /* REQUIRED. LD is flaky without it. */
} >rom =0
.rodata :
{
*(.rodata)
*all.rodata*(*)
*(.roda)
*(.rodata.*)
*(.gnu.linkonce.r*)
SORT(CONSTRUCTORS)
. = ALIGN(4); /* REQUIRED. LD is flaky without it. */
} >rom = 0xff
.ARM.extab : { *(.ARM.extab* .gnu.linkonce.armextab.*) } >rom
__exidx_start = .;
.ARM.exidx : { *(.ARM.exidx* .gnu.linkonce.armexidx.*) } >rom
__exidx_end = .;
.ctors :
{
/* gcc uses crtbegin.o to find the start of the constructors, so
we make sure it is first. Because this is a wildcard, it
doesn't matter if the user does not actually link against
crtbegin.o; the linker won't look for a file to match a
wildcard. The wildcard also means that it doesn't matter which
directory crtbegin.o is in. */
KEEP (*crtbegin.o(.ctors))
KEEP (*(EXCLUDE_FILE (*crtend.o) .ctors))
KEEP (*(SORT(.ctors.*)))
KEEP (*(.ctors))
. = ALIGN(4); /* REQUIRED. LD is flaky without it. */
} >rom = 0
.dtors :
{
KEEP (*crtbegin.o(.dtors))
KEEP (*(EXCLUDE_FILE (*crtend.o) .dtors))
KEEP (*(SORT(.dtors.*)))
KEEP (*(.dtors))
. = ALIGN(4); /* REQUIRED. LD is flaky without it. */
} >rom = 0
.eh_frame :
{
KEEP (*(.eh_frame))
. = ALIGN(4); /* REQUIRED. LD is flaky without it. */
} >rom = 0
.gcc_except_table :
{
*(.gcc_except_table)
. = ALIGN(4); /* REQUIRED. LD is flaky without it. */
} >rom = 0
__iwram_lma = .;
.iwram __iwram_start : AT (__iwram_lma)
{
__iwram_start__ = ABSOLUTE(.) ;
*(.iwram .iwram*)
*iwram.*(.text* .data*)
. = ALIGN(4); /* REQUIRED. LD is flaky without it. */
__iwram_end__ = ABSOLUTE(.) ;
} >iwram = 0xff
__data_lma = __iwram_lma + SIZEOF(.iwram) ;
.bss ALIGN(4) (NOLOAD) :
{
__bss_start = ABSOLUTE(.);
__bss_start__ = ABSOLUTE(.);
*(.dynbss)
*(.gnu.linkonce.b*)
*(.bss*)
*(COMMON)
. = ALIGN(4); /* REQUIRED. LD is flaky without it. */
__bss_end__ = ABSOLUTE(.);
} AT>iwram
.data ALIGN(4) : AT (__data_lma)
{
__data_start__ = ABSOLUTE(.);
*(.data*)
*(.gnu.linkonce.d*)
CONSTRUCTORS
. = ALIGN(4);
} >iwram = 0xff
__preinit_lma = __data_lma + SIZEOF(.data);
.preinit_array ALIGN(4) : AT (__preinit_lma)
{
__preinit_array_start = ABSOLUTE(.);
KEEP (*(.preinit_array))
__preinit_array_end = ABSOLUTE(.);
} >iwram
__init_lma = __preinit_lma + SIZEOF(.preinit_array);
.init_array ALIGN(4) : AT (__init_lma)
{
__init_array_start = ABSOLUTE(.);
KEEP (*(SORT(.init_array.*)))
KEEP (*(.init_array))
__init_array_end = ABSOLUTE(.);
} >iwram
__fini_lma = __init_lma + SIZEOF(.init_array);
.fini_array ALIGN(4) : AT (__fini_lma)
{
__fini_array_start = ABSOLUTE(.);
KEEP (*(SORT(.fini_array.*)))
KEEP (*(.fini_array))
__fini_array_end = ABSOLUTE(.);
} >iwram
__jcr_lma = __fini_lma + SIZEOF(.fini_array);
.jcr ALIGN(4) : AT (__jcr_lma) { KEEP (*(.jcr)) } >iwram
__data_end__ = ABSOLUTE(.);
__iwram_overlay_lma = __jcr_lma + SIZEOF(.jcr);
__iwram_overlay_start = . ;
OVERLAY ALIGN(4) : NOCROSSREFS AT (__iwram_overlay_lma)
{
.iwram0 { *(.iwram0) . = ALIGN(4);}
.iwram1 { *(.iwram1) . = ALIGN(4);}
.iwram2 { *(.iwram2) . = ALIGN(4);}
.iwram3 { *(.iwram3) . = ALIGN(4);}
.iwram4 { *(.iwram4) . = ALIGN(4);}
.iwram5 { *(.iwram5) . = ALIGN(4);}
.iwram6 { *(.iwram6) . = ALIGN(4);}
.iwram7 { *(.iwram7) . = ALIGN(4);}
.iwram8 { *(.iwram8) . = ALIGN(4);}
.iwram9 { *(.iwram9) . = ALIGN(4);}
}>iwram = 0xff
__iwram_overlay_end = . ;
__ewram_lma = __iwram_overlay_lma + (__iwram_overlay_end - __iwram_overlay_start) ;
__iheap_start = . ;
__ewram_start = ORIGIN(ewram);
.ewram __ewram_start : AT (__ewram_lma)
{
*(.ewram*)
. = ALIGN(4); /* REQUIRED. LD is flaky without it. */
__ewram_end = ABSOLUTE(.);
}>ewram = 0xff
__pad_lma = __ewram_lma + SIZEOF(.ewram);
.sbss ALIGN(4)(NOLOAD):
{
__sbss_start__ = ABSOLUTE(.);
*(.sbss*)
. = ALIGN(4);
__sbss_end__ = ABSOLUTE(.);
__end__ = ABSOLUTE(.);
__eheap_start = ABSOLUTE(.);
} AT>ewram
/* EZF Advance strips trailing 0xff bytes, add a pad section so nothing important is removed */
.pad ALIGN(4) : AT (__pad_lma)
{
LONG(0x52416b64)
LONG(0x4d)
. = ALIGN(4); /* REQUIRED. LD is flaky without it. */
} = 0xff
__rom_end__ = __pad_lma + SIZEOF(.pad);
/* Stabs debugging sections. */
.stab 0 : { *(.stab) }
.stabstr 0 : { *(.stabstr) }
.stab.excl 0 : { *(.stab.excl) }
.stab.exclstr 0 : { *(.stab.exclstr) }
.stab.index 0 : { *(.stab.index) }
.stab.indexstr 0 : { *(.stab.indexstr) }
.comment 0 : { *(.comment) }
/* DWARF debug sections.
Symbols in the DWARF debugging sections are relative to the beginning
of the section so we begin them at 0. */
/* DWARF 1 */
.debug 0 : { *(.debug) }
.line 0 : { *(.line) }
/* GNU DWARF 1 extensions */
.debug_srcinfo 0 : { *(.debug_srcinfo) }
.debug_sfnames 0 : { *(.debug_sfnames) }
/* DWARF 1.1 and DWARF 2 */
.debug_aranges 0 : { *(.debug_aranges) }
.debug_pubnames 0 : { *(.debug_pubnames) }
/* DWARF 2 */
.debug_info 0 : { *(.debug_info) }
.debug_abbrev 0 : { *(.debug_abbrev) }
.debug_line 0 : { *(.debug_line) }
.debug_frame 0 : { *(.debug_frame) }
.debug_str 0 : { *(.debug_str) }
.debug_loc 0 : { *(.debug_loc) }
.debug_macinfo 0 : { *(.debug_macinfo) }
/* SGI/MIPS DWARF 2 extensions */
.debug_weaknames 0 : { *(.debug_weaknames) }
.debug_funcnames 0 : { *(.debug_funcnames) }
.debug_typenames 0 : { *(.debug_typenames) }
.debug_varnames 0 : { *(.debug_varnames) }
.stack 0x80000 : { _stack = .; *(.stack) }
/* These must appear regardless of . */
.note.gnu.arm.ident 0 : { KEEP (*(.note.gnu.arm.ident)) }
.ARM.attributes 0 : { KEEP (*(.ARM.attributes)) }
/DISCARD/ : { *(.note.GNU-stack) }
}
MEMORY {
rom : ORIGIN = 0x08000000, LENGTH = 32M
iwram : ORIGIN = 0x03000000, LENGTH = 32K
ewram : ORIGIN = 0x02000000, LENGTH = 256K
}
__text_start = ORIGIN(rom);
__eheap_end = ORIGIN(ewram) + LENGTH(ewram);
__iwram_start = ORIGIN(iwram);
__iwram_top = ORIGIN(iwram) + LENGTH(iwram);;
__sp_irq = __iwram_top - 0x060;
__sp_usr = __sp_irq - 0x0a0;
__irq_flags = 0x03007ff8;
各計算を行うと__sp_irqは0x3007FA0(0x3000000 + 0x8000 - 0x60)、__sp_usrは0x3007F00(0x3007FA0 - 0x0a0)となります。GBATEKでは次のような説明をされています。気をつけないといけないのは割り込み用のスタックが160サイズしかないことです。割り込み処理を作る際には注意してください。
| アドレス | サイズ | 用途 |
| 3007FFCh | 4 | Pointer to user IRQ handler (32bit ARM code) |
| 3007FF8h | 4 | Interrupt Check Flag (for IntrWait/VBlankIntrWait functions) |
| 3007FF4h | 4 | Pointer to Sound Buffer |
| 3007FE0h | 16 | Allocated Area |
| 3007FA0h | 64 | Default area for SP_svc Supervisor Stack (4 words/time) |
| 3007F00h | 160 | Default area for SP_irq Interrupt Stack (6 words/time) |
Memory below 7F00h is free for User Stack and user data. The three stack pointers are initially initialized at the TOP of the respective areas: SP_svc=03007FE0h SP_irq=03007FA0h SP_usr=03007F00h
IWRAM_CODE int main(void)
{
REG_WSCNT = 0x4317;
u32 i = 0xbeefbeef;
u32 j = 0;
u32 k = 0;
char a[10];
BgInit();
IrqInit();
BgDrawPrintf(0, 0, "&i = %X", (u32)&i);
BgDrawPrintf(0, 1, "&j = %X", (u32)&j);
BgDrawPrintf(0, 2, "&k = %X", (u32)&k);
for(i=0; i<10; i++)
{
BgDrawPrintf(0, 4+i, "&a[%d] = %X", i, (u32)&a[i]);
}
for(;;)
{
VBlankIntrWait();
}
}
結果を先に載せますとa[9]が一番新しいスタック領域になります。この値はどこからやってくるのかNO$GBAをデバッグしてみていきます。まずコンパイルされたmapファイルからmain関数のアドレスは0x080001f8ということがわかります。ここをブレークポイントにしましょう。
TODO 図
スタックはr17で値は0x03007F00です。さらに0xbeefbeefを代入している部分までブレークポイントして実行してみます。結果のスタック領域を乗せるとこのようになりました。
080000fc ldr sp, =__sp_usr @ Set user stack
0x080001f8 main 0x030005fc BgDrawPrintf
