On Tue, Sep 23, 2014 at 11:39 AM, Bin Meng <bmeng...@gmail.com> wrote: > On Tue, Sep 23, 2014 at 5:11 PM, Bin Meng <bmeng...@gmail.com> wrote: >> >> Sorry I still don't get it. The inline-asm codes are put in the very end >> of the test function just before return, so the clobbered registers are >> not used by gcc. The %edx gets overwritten before the inline-asm block. >> >> I just did a modification to the inline-asm codes to indicate to gcc that >> %edx is clobbered, but it did not help. >> > > PS: if turning on WORKAROUND define in my test code, the generated codes > are correct. > > I believe the issue is not with the inline assembly constraints but with > '-Os' plus '-regparm=3' combination. With '-Os' gcc optimization goes too > far to generate nothing for the C code 'params.a = d;' and gcc simply > takes %edx (supposed to be the 2nd parameter of test function) for a > scratch register.
Well, you don't use 'params'. the "m" (params_ptr) constraint only puts the pointer in memory, it doesn't make the pointed-to value used. Richard. > Regards, > Bin