diff options
| -rw-r--r-- | arch/x86/include/asm/calling.h | 56 |
1 files changed, 53 insertions, 3 deletions
diff --git a/arch/x86/include/asm/calling.h b/arch/x86/include/asm/calling.h index 2bc162e0ec6..0e63c9a2a8d 100644 --- a/arch/x86/include/asm/calling.h +++ b/arch/x86/include/asm/calling.h @@ -1,5 +1,55 @@ /* - * Some macros to handle stack frames in assembly. + + x86 function call convention, 64-bit: + ------------------------------------- + arguments | callee-saved | extra caller-saved | return + [callee-clobbered] | | [callee-clobbered] | + --------------------------------------------------------------------------- + rdi rsi rdx rcx r8-9 | rbx rbp [*] r12-15 | r10-11 | rax, rdx [**] + + ( rsp is obviously invariant across normal function calls. (gcc can 'merge' + functions when it sees tail-call optimization possibilities) rflags is + clobbered. Leftover arguments are passed over the stack frame.) + + [*] In the frame-pointers case rbp is fixed to the stack frame. + + [**] for struct return values wider than 64 bits the return convention is a + bit more complex: up to 128 bits width we return small structures + straight in rax, rdx. For structures larger than that (3 words or + larger) the caller puts a pointer to an on-stack return struct + [allocated in the caller's stack frame] into the first argument - i.e. + into rdi. All other arguments shift up by one in this case. + Fortunately this case is rare in the kernel. + +For 32-bit we have the following conventions - kernel is built with +-mregparm=3 and -freg-struct-return: + + x86 function calling convention, 32-bit: + ---------------------------------------- + arguments | callee-saved | extra caller-saved | return + [callee-clobbered] | | [callee-clobbered] | + ------------------------------------------------------------------------- + eax edx ecx | ebx edi esi ebp [*] | <none> | eax, edx [**] + + ( here too esp is obviously invariant across normal function calls. eflags + is clobbered. Leftover arguments are passed over the stack frame. ) + + [*] In the frame-pointers case ebp is fixed to the stack frame. + + [**] We build with -freg-struct-return, which on 32-bit means similar + semantics as on 64-bit: edx can be used for a second return value + (i.e. covering integer and structure sizes up to 64 bits) - after that + it gets more complex and more expensive: 3-word or larger struct returns + get done in the caller's frame and the pointer to the return struct goes + into regparm0, i.e. eax - the other arguments shift up and the + function's register parameters degenerate to regparm=2 in essence. + +*/ + + +/* + * 64-bit system call stack frame layout defines and helpers, + * for assembly code: */ #define R15 0 @@ -9,7 +59,7 @@ #define RBP 32 #define RBX 40 -/* arguments: interrupts/non tracing syscalls only save upto here*/ +/* arguments: interrupts/non tracing syscalls only save up to here: */ #define R11 48 #define R10 56 #define R9 64 @@ -22,7 +72,7 @@ #define ORIG_RAX 120 /* + error_code */ /* end of arguments */ -/* cpu exception frame or undefined in case of fast syscall. */ +/* cpu exception frame or undefined in case of fast syscall: */ #define RIP 128 #define CS 136 #define EFLAGS 144 |