Messages in this thread | | | Date | Tue, 3 Feb 2009 19:48:13 +0100 | From | Ingo Molnar <> | Subject | Re: [tip:x86/asm] x86: document 64-bit and 32-bit function call convention ABI |
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* Randy Dunlap <randy.dunlap@oracle.com> wrote:
> Ingo Molnar wrote: > > - also clean up the calling.h file a tiny bit > > > > Signed-off-by: Ingo Molnar <mingo@elte.hu> > > --- > > 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 2bc162e..2d36d42 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 ebp is fixed to the stack frame. > > ebp or rbp ?
rbp - fixed it, thanks.
> > + > > + [**] 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 > > What size does "word" mean here? > and is it rdx:rax (high:low)? Can it be so written? > or at least say which of rax, rdx is high (most significant) and > which is low (least significant).
no, word is the normal meaning: natural machine word. 32-bit on 32-bit x86, 64-bit on 64-bit x86.
> > > + 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 build with > > built
fixed that too.
> > +-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. > > + > > Same high:low comments here. > > > +*/ > > + > > + > > +/* > > + * 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 upto here: */ > > up to
pre-existing typo but worth fixing indeed.
Ingo
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