Richard Sandiford wrote: [snip] > > Only for old compilers. For current (>= 3.4) ones you can use the "R" > > constraint and get exactly what you need. > > Right. IMO, this is exactly the right fix. It should be backward > compatible with old toolchains too. > > FYI, the 'R' constraint has been kept around specifically for inline asms. > gcc itself no longer uses it. I tried to use "R" in atomic.h but this failed in some (but not all) cases with include/asm/atomic.h:64: error: inconsistent operand constraints in an asm' where the argument happens to be a member of a global struct. Simple testcases work, however, as well as PIC code. [snip] > > I discussed this with Richard Sandiford a while ago, and the conclusion > > was to implement an explicit --msym32 option for both gcc and gas to > > improve register scheduling and get rid of the gas hack. So far, nobody > > came around to actually do the work for it. > > True. FWIW, it's trivial to add this option to gcc. As far as I remember, > the stumbling block was whether we should mark the objects in some way, > and whether the linker ought to check for overflow. Both might be nice but isn't exactly reqired. The use of --msym32 will be limited to ELF64 non-PIC code, which is only used in kernels or other stand-alone programs with limited exposure to other binaries with incompatible code models. Thiemo
