编译到ARM我得到"错误:尝试在Thumb-only处理器上使用ARM指令"

Question

以下命令

/usr/bin/arm-linux-gnueabihf-gcc -O3 -DNDEBUG -march=armv7-a -mfloat-abi=hard -fPIC -fno-builtin -fno-exceptions -fomit-frame-pointer -funwind-tables -fno-stack-protector -fvisibility=hidden -fvisibility-inlines-hidden -fno-function-sections -fno-lto -g -Wno-variadic-macros -Wno-non-virtual-dtor -o testAsm.S.o -c testAsm.S

在以下程序集文件中testAsm.S:

    .syntax unified
    .arch armv7
    .fpu vfpv3
    .code 32
    .global _functionPointer
    .p2align 2
    .global _asmFunction
    .type _asmFunction, %function
_asmFunction:
    PUSH {r1-r3,lr}
    VPUSH {d0-d7}
    MOVW r1,#:lower16:_functionPointer
    MOVT r1,#:upper16:_functionPointer
    LDR r2, [r1]
    CMP r2, #0
    BEQ asmFunction_restore
    MOV r1, #0
    BLX r2
asmFunction_restore:
    VPOP {d0-d7}
    POP {r1-r3,pc}

每条指令产生以下错误

错误:尝试在仅Thumb处理器上使用ARM指令

具体来说,下面是输出:

testAsm.S: Assembler messages:
testAsm.S:10: Error: attempt to use an ARM instruction on a Thumb-only processor -- `push {r1-r3,lr}'
testAsm.S:11: Error: attempt to use an ARM instruction on a Thumb-only processor -- `vpush {d0-d7}'
testAsm.S:12: Error: attempt to use an ARM instruction on a Thumb-only processor -- `movw r1,#:lower16:_functionPointer'
testAsm.S:13: Error: attempt to use an ARM instruction on a Thumb-only processor -- `movt r1,#:upper16:_functionPointer'
testAsm.S:14: Error: attempt to use an ARM instruction on a Thumb-only processor -- `ldr r2,[r1]'
testAsm.S:15: Error: attempt to use an ARM instruction on a Thumb-only processor -- `cmp r2,#0'
testAsm.S:16: Error: attempt to use an ARM instruction on a Thumb-only processor -- `beq asmFunction_restore'
testAsm.S:17: Error: attempt to use an ARM instruction on a Thumb-only processor -- `mov r1,#0'
testAsm.S:18: Error: attempt to use an ARM instruction on a Thumb-only processor -- `blx r2'
testAsm.S:20: Error: attempt to use an ARM instruction on a Thumb-only processor -- `vpop {d0-d7}'
testAsm.S:21: Error: attempt to use an ARM instruction on a Thumb-only processor -- `pop {r1-r3,pc}'

我试着为ARM编译.为什么会说Thumb-only模式？

编辑:显然,更改程序集文件.arch armv7以.arch armv7a解决问题.

Answer 1

GNU arch=armv7可能是令人困惑的,代表了ARMv7-A和ARMv7-M 的交集(使其具有可疑的实用性).因此将它与.code 32(相当于-marm命令行选项)结合起来,它告诉汇编程序汇编到ARM编码,而ARMv7-M不支持ARM编码,这使得它无法组装任何东西.

当然,简单地在指令或选项中停止并引发错误会使其处于不可能的情况对于GAS而言太过明智了,所以相反它继续进行并且无法单独汇编每条指令......