Wu Zhangjin <wuzhangjin@xxxxxxxxx> writes: > (Added linux-mips mailing list and the other people to the CC list.) > > On Thu, 2009-10-22 at 04:37 -0700, pajko wrote: > [...] >> > >> >> All this stuff can be avoided having PROFILE_BEFORE_PROLOGUE enabled in GCC >> (gcc/config/mips/mips.h), like it is done one several other architectures. >> Some of them even require it to be set for a working _mcount. >> Putting the call of _mcount before the function prologue should make no harm >> (it's working for me), and this way RA can be hooked for function graph >> tracing >> before it is saved to stack in the function prologue. Thus there will be no >> difference between leaf and non-leaf functions. > > Good idea! Seems PROFILE_BEFORE_PROLOGUE is commented by default in > gcc/config/mips/mips.h of gcc 4.4: > > /* #define PROFILE_BEFORE_PROLOGUE */ > > if we enable this macro, the handling will be the same to non-leaf and > leaf function, so, David's patch to gcc is not need again. Defining PROFILE_BEFORE_PROLOGUE isn't correct for abicalls code, because "jal _mcount" is a macro that loads _mcount from the GOT into $25. We don't have access to $28 at the beginning of the function, and we mustn't clobber the incoming value of $25. So we could only make this change for non-abicalls code. It's then a choice between (a) having new non-abicalls-specific behaviour or (b) going with David's patch. The advantage of (a) is that the linux code is slightly simpler. The disadvantage is that it makes the _mcount interface differ between -mabicalls and -mno-abicalls. And IMO the disadvantage outweights the advantage. If this new behaviour is useful for linux, it could easily be useful for userspace too. And with the new PLT support, non-shared abicalls code is supposed to be link-compatible with non-abicalls code. I think David's patch is the way to go. Richard
