當編譯該C++代碼:GCC產生的未對齊 「LDRD」 指令
#include "../SM64DS_2.h"
//@021026a0, hooks: 0x020bddb8, 0x020bde0c
void CancelPowerups(Player& player)
{
if(player.isFreezeFramePeach)
{
player.isFreezeFramePeach = false;
player.EndMusic(0x33);
}
if(player.isDashyToad)
{
player.isDashyToad = false;
player.EndMusic(0x33);
}
}
//hook: 0x020b98f8
void EnableFreezeFramePeach(Player& player)
{
//TODO: Show message on first use
player.isFreezeFramePeach = true;
player.flowerPowerTimer = 600;
player.SetMusic(0x33);
}
//hook: 0x020b9904
void EnableDashyToad(Player& player)
{
//TODO: Show message on first use
player.isDashyToad = true;
player.flowerPowerTimer = 600;
player.SetMusic(0x33);
}
//hook: 0x020e4f10
void WorkDashyToadPart1(Player& player)
{
//TODO: Deal with speed of walking animation
if(player.isDashyToad)
{
player.horzSpeed /= 2;
player.isSpeedHalfed = true;
if(player.walkOnWaterTimer == 61)
++player.walkOnWaterTimer;
}
}
//hook: 0x020e52e8
void WorkDashyToadPart2(Player& player)
{
if(player.isSpeedHalfed)
{
player.horzSpeed *= 2;
player.isSpeedHalfed = false;
player.dashyToadParticleSysID = Particle::System::New(player.dashyToadParticleSysID,
0x4a,
player.pos.x,
player.pos.y + Fix12i(72),
player.pos.z,
nullptr,
nullptr);
}
}
與GCC
arm-none-eabi-g++ -MMD -MP -MF /c/Users/Joshua/Documents/desmume-0.9.11-win64/SM64DSe/SM64DSe/ASMPatchTemplate/build/PeachToadAbilities.d -g -Wall -O2 -march=armv5te -mtune=arm946e-s -fomit-frame-pointer -ffast-math -iquote /c/Users/Joshua/Documents/desmume-0.9.11-win64/SM64DSe/SM64DSe/ASMPatchTemplate/include -I/c/devkitPro/libnds/include -I/c/devkitPro/devkitARM/include -I/c/devkitPro/devkitARM/arm-none-eabi/include -I/c/Users/Joshua/Documents/desmume-0.9.11-win64/SM64DSe/SM64DSe/ASMPatchTemplate/build -DARM9 -nodefaultlibs -I. -fno-builtin -c --std=c++14 -fno-rtti -fno-exceptions -Wa,-adl=PeachToadAbilities.lst -c /c/Users/Joshua/Documents/desmume-0.9.11-win64/SM64DSe/SM64DSe/ASMPatchTemplate/source/C_PeachToadAbilities/PeachToadAbilities.cpp -o PeachToadAbilities.o
(注意特別是該架構的ARMv5TE和CPU是以下標誌ARM946E-S) 以下ASM是在過去的函數生成:
push {r4, lr}
mov r4, r0
mov r1, #0x0
ldrd r2, [r4, #0x5c]
ldr ip, [r0, #0x98]
ldr r0, [r0, #0x280]
lsl ip, ip, #0x1
str ip, [r4, #0x98]
ldr ip, [r4, #0x64]
sub sp, sp, #0x10
strb r1, [r4, #0x27d]
add r3, r3, #0x48000
str r1, [sp, #0x8]
str r1, [sp, #0x4]
str ip, [sp]
mov r1, #0x4a
bl _ZN8Particle6System3NewEjj5Fix12IiES2_S2_PK11Vector3_16fPNS_8CallbackE
str r0, [r4, #0x280]
add sp, sp, #0x10
pop {r4, pc}
對於康特xt,這是一款任天堂DS遊戲的ROM破解版。播放器結構是4字節對齊的,並且在偏移0x5C處是播放器的位置,這是3的結構。Fix12 <int>(A Fix12 <int>是1個4字節整數的結構)。
問題是gcc生成一個不能被證明訪問8字節對齊地址的「ldrd」指令(它不應該知道「player」在哪,除此之外,0x5C不是8的倍數) 。我看過的ARM文檔說,對於ARMv5,加載未對齊的雙字是未定義的行爲。但是,沒有$ gba和DeSmuME假設地址是4字節對齊時的這種訪問仍然從該地址加載一個8字節的值。對於ARM946E-S CPU上的ARMv5TE,這是正確的行爲嗎? (我沒有在實際的DS上測試過,因爲我沒有閃存卡。)
看起來像是從後來的Arm體系結構中刪除了8字節的對齊要求,而GCC沒有遵守舊的要求。可能的解決方法可能是僅通過編譯ARMv5T來禁用這些指令? – NickJH