如何编写从汇编代码调用的C函数
我需要编写一个C函数，它将从linux内核中的汇编代码中调用。
应该考虑哪些特殊问题？
我有一些想法，但任何人都可以提供更多细节：
（1）召集会议
确保组件中的呼叫者和c中的被叫者握手良好。 但是我应该使用哪种调用约定？ 如何声明c函数并在汇编代码中声明它？
（2）保护寄存器
在调用之前，应将某些寄存器保存在程序集中。 我粗略记得他们是eax，ecx和edx。 但我不需要保存它们，除非我需要在调用C函数之前引用旧值，对吧？
还有什么其他问题？
当您使用linux-kernel标记的任务时，请查看以下内核头文件： arch / x86 / include / asm / calling.h 。
3 x86 function call convention, 64-bit: 4 ------------------------------------- 5 arguments | callee-saved | extra caller-saved | return 6 [callee-clobbered] | | [callee-clobbered] | 7 --------------------------------------------------------------------------- 8 rdi rsi rdx rcx r8-9 | rbx rbp [*] r12-15 | r10-11 | rax, rdx [**] 9 10 ( rsp is obviously invariant across normal function calls. (gcc can 'merge' 11 functions when it sees tail-call optimization possibilities) rflags is 12 clobbered. Leftover arguments are passed over the stack frame.) 13 14 [*] In the frame-pointers case rbp is fixed to the stack frame. 15 16 [**] for struct return values wider than 64 bits the return convention is a 17 bit more complex: up to 128 bits width we return small structures 18 straight in rax, rdx. For structures larger than that (3 words or 19 larger) the caller puts a pointer to an on-stack return struct 20 [allocated in the caller's stack frame] into the first argument - ie 21 into rdi. All other arguments shift up by one in this case. 22 Fortunately this case is rare in the kernel. 23 24 For 32-bit we have the following conventions - kernel is built with 25 -mregparm=3 and -freg-struct-return: 26 27 x86 function calling convention, 32-bit: 28 ---------------------------------------- 29 arguments | callee-saved | extra caller-saved | return 30 [callee-clobbered] | | [callee-clobbered] | 31 ------------------------------------------------------------------------- 32 eax edx ecx | ebx edi esi ebp [*] | | eax, edx [**] 33 34 ( here too esp is obviously invariant across normal function calls. eflags 35 is clobbered. Leftover arguments are passed over the stack frame. ) 36 37 [*] In the frame-pointers case ebp is fixed to the stack frame. 38 39 [**] We build with -freg-struct-return, which on 32-bit means similar 40 semantics as on 64-bit: edx can be used for a second return value 41 (ie covering integer and structure sizes up to 64 bits) - after that 42 it gets more complex and more expensive: 3-word or larger struct returns 43 get done in the caller's frame and the pointer to the return struct goes 44 into regparm0, ie eax - the other arguments shift up and the 45 function's register parameters degenerate to regparm=2 in essence.