我正在努力让一些x86程序集在Core 2 Duo Mac上进行编译。使用clang会为以下语句返回invalid operand
错误:
asm volatile ("subl %0,%%esp" :: "r"(foobar) : "cc", "sp");
foobar
是long
的位置。我想知道sp
关键字在clobber列表中意味着什么,因为GCC / llvm doc和Google都没有对它们有所了解。有人知道一个完整的clobber关键词列表吗?
答案 0 :(得分:4)
肯定会是堆栈指针,尤其是,因为你实际上是从堆栈指针esp
中减去了一些东西。您可能已经知道了这一点,但是,以防万一,cc
是条件代码寄存器(标志等)。
为什么它是sp
而不是esp
,我无法告诉你,但是,如果你遇到错误,那就是我要改变的第一件事,看看这是不是问题。< / p>
你应该放在那里的值是所有可能被破坏的寄存器(除了为gcc
已经知道的输出明确列出的那些将会改变的那些)和特殊值{{ 1}}如果您不希望memory
假设任何缓存的内存值仍然有效。
寄存器当然取决于底层架构。不确定这是一个全面的列表,但它是我曾经使用或需要使用的所有内容。
答案 1 :(得分:1)
查看gcc-4.4.3/gcc/config/i386/i386.h :2036文件我得出结论,“sp”是特定于gcc的“esp”别名:
/* How to refer to registers in assembler output.
This sequence is indexed by compiler's hard-register-number (see above). */
/* In order to refer to the first 8 regs as 32-bit regs, prefix an "e".
For non floating point regs, the following are the HImode names.
For float regs, the stack top is sometimes referred to as "%st(0)"
instead of just "%st". PRINT_OPERAND handles this with the "y" code. */
#define HI_REGISTER_NAMES \
{"ax","dx","cx","bx","si","di","bp","sp", \
"st","st(1)","st(2)","st(3)","st(4)","st(5)","st(6)","st(7)", \
"argp", "flags", "fpsr", "fpcr", "frame", \
"xmm0","xmm1","xmm2","xmm3","xmm4","xmm5","xmm6","xmm7", \
"mm0", "mm1", "mm2", "mm3", "mm4", "mm5", "mm6", "mm7", \
"r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15", \
"xmm8", "xmm9", "xmm10", "xmm11", "xmm12", "xmm13", "xmm14", "xmm15"}
#define REGISTER_NAMES HI_REGISTER_NAMES
/* Table of additional register names to use in user input. */
#define ADDITIONAL_REGISTER_NAMES \
{ { "eax", 0 }, { "edx", 1 }, { "ecx", 2 }, { "ebx", 3 }, \
{ "esi", 4 }, { "edi", 5 }, { "ebp", 6 }, { "esp", 7 }, \
{ "rax", 0 }, { "rdx", 1 }, { "rcx", 2 }, { "rbx", 3 }, \
{ "rsi", 4 }, { "rdi", 5 }, { "rbp", 6 }, { "rsp", 7 }, \
{ "al", 0 }, { "dl", 1 }, { "cl", 2 }, { "bl", 3 }, \
{ "ah", 0 }, { "dh", 1 }, { "ch", 2 }, { "bh", 3 } }
“sp”和“esp”(以及“rsp”)都将代码寄存器编号为7。
因此,此代码对于GCC是合法的;但是你想让它变得便携(可以通过clang编译),将“sp”改为“esp”。这个补丁不会改变gcc逻辑,并且可以让你用clang构建它。
==更新==
gcc也有可能存储clobbers的寄存器访问大小。这是asm寄存器的检查函数 - clobbers conflict(gcc / stmt.c):
tree_conflicts_with_clobbers_p (tree t, HARD_REG_SET *clobbered_regs)
{
/* Conflicts between asm-declared register variables and the clobber
list are not allowed. */
tree overlap = tree_overlaps_hard_reg_set (t, clobbered_regs);
通过HARD_REG_SET检查冲突(重叠),其大小为52位:
gcc/hard-reg-set.h :50。 Hard_reg_set具有FIRST_PSEUDO位的长度,向上舍入以完全填充fastint。
#define HARD_REG_SET_LONGS \
((FIRST_PSEUDO_REGISTER + HOST_BITS_PER_WIDEST_FAST_INT - 1) \
/ HOST_BITS_PER_WIDEST_FAST_INT)
typedef HARD_REG_ELT_TYPE HARD_REG_SET[HARD_REG_SET_LONGS];
i386/i386.h :865:#define FIRST_PSEUDO_REGISTER 53
:882 same file在HARD_REG_SET中有一个寄存器列表:
#define FIXED_REGISTERS \
/*ax,dx,cx,bx,si,di,bp,sp,st,st1,st2,st3,st4,st5,st6,st7*/ \
{ 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, \
/*arg,flags,fpsr,fpcr,frame*/ \
1, 1, 1, 1, 1, \
/*xmm0,xmm1,xmm2,xmm3,xmm4,xmm5,xmm6,xmm7*/ \
0, 0, 0, 0, 0, 0, 0, 0, \
/* mm0, mm1, mm2, mm3, mm4, mm5, mm6, mm7*/ \
0, 0, 0, 0, 0, 0, 0, 0, \
/* r8, r9, r10, r11, r12, r13, r14, r15*/ \
2, 2, 2, 2, 2, 2, 2, 2, \
/*xmm8,xmm9,xmm10,xmm11,xmm12,xmm13,xmm14,xmm15*/ \
2, 2, 2, 2, 2, 2, 2, 2 }
因此,在没有大小字段检查的情况下检查register-clobber冲突(对于非mm / xmm regs)。