H. Peter Anvin wrote: > On 11/24/2009 07:46 AM, Andrew Haley wrote: >>> Yes, a lot. The difference is that -maccumulate-outgoing-args allocates >>> space for arguments of the callee with most arguments in the prologue, using >>> subtraction from sp, then to pass arguments uses movl XXX, 4(%esp) etc. >>> and the stack pointer doesn't usually change within the function (except for >>> alloca/VLAs). >>> With -mno-accumulate-outgoing-args args are pushed using push instructions >>> and stack pointer is constantly changing. >> Alright. So, it is possible in theory for gcc to generate code that >> only uses -maccumulate-outgoing-args when it needs to realign SP. >> And, therefore, we could have a nice option for the kernel: one with >> (mostly) good code density and never generates the bizarre code >> sequence in the prologue. > > If we're changing gcc anyway, then let's add the option of intercepting > the function at the point where the machine state is well-defined by > ABI, which is before the function stack frame is set up.
Hmm. On the x86 I suppose we could just inject a naked call instruction, but not all aeches allow us to call anything before we've saved the return address. Or are you talking x86 only? Andrew.
