如何在 GCC 中编写 .syntax 统一的 UAL ARMv7 内联汇编? [英] How to write .syntax unified UAL ARMv7 inline assembly in GCC?

问题描述

我想编写统一的程序集来摆脱烦人的 # 在我的文字前面提到的:ARM 汇编中的立即数是否需要散列?

I want to write unified assembly to get rid of pesky # in front of my literals as mentioned at: Is the hash required for immediate values in ARM assembly?

这是一个带有#的最小非统一代码:

This is a minimal non-unified code with #:

#include <assert.h>
#include <inttypes.h>

int main(void) {
    uint32_t io = 0;
    __asm__ (
        "add %0, %0, #1;"
        : "+r" (io)
        :
        :
    );
    assert(io == 1);
}

在 QEMU 下编译后运行良好:

which compiles and later runs fine under QEMU:

arm-linux-gnueabihf-gcc -c -ggdb3 -march=armv7-a -pedantic -std=c99 -Wall -Wextra \
  -fno-pie -no-pie -marm -o 'tmp.o' 'tmp.c'

如果我尝试删除 #，则代码失败:

If I try to remove the #, then the code fails with:

/tmp/user/20321/ccoBzpSK.s: Assembler messages:
/tmp/user/20321/ccoBzpSK.s:51: Error: shift expression expected -- `add r3,r3,1'

正如预期的那样，因为非统一似乎是默认设置.

as expected, since non-unified seems to be the default.

如何让它发挥作用?

我找到了有希望的选择:

I found the promising option:

gcc -masm-syntax-unified

但添加它没有帮助.

如果我改写:

".syntax unified; add %0, %0, #1;"

然后它可以工作，但我必须为每个不切实际的 __asm__ 这样做.

then it works, but I would have to do that for every __asm__ which is not practical.

UI 还发现，如果没有 -marm，那么它确实使用了统一汇编，但是它生成了我不想要的拇指代码.

UI also found that without -marm, then it does use unified assembly, but it generates thumb code, which I don't want.

也许这个bug是问题的根本原因:https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88648

Maybe this bug is the root cause of the problem: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88648

在 arm-linux-gnueabi-gcc 5.4.0、Ubuntu 18.04 中测试.

Tested in arm-linux-gnueabi-gcc 5.4.0, Ubuntu 18.04.

推荐答案

Devs 很快再次回复了这个问题:https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88648#c3 并在以下位置提交了补丁:https://github.com/gcc-mirror/gcc/commit/2fd2b9b8484d201b9b84d201b9b84d201b9b84d84d201b9b84d201b9b84d72ad98d201b921d75bd9代码>-masm-syntax-unified.太棒了！

Devs replied again soon to the issue: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88648#c3 and a patch was committed at: https://github.com/gcc-mirror/gcc/commit/2fd2b9b8425f9fc4ad98d48a0ca41b921dd75bd9 (post 8.2.0) fixing -masm-syntax-unified. Awesome!

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