Nathan, This patch will do what you intend it to do. However, I am not sure in part related to VxWorks. The logic behind this patch is that -mno-pic-data-is-text-relative should enable -msingle-pic-base because otherwise it will be useless. The logic itself is orthogonal to OS. So I am not convinced the 'else if' shouldn't be just 'if'. It should not change VxWorks behaviour if VxWorks enables -msingle-pic-base explicitly. Or otherwise there is at least one use case that -mno-pic-data-is-text-relative can be used without -msingle-pic-base, which breaks the logic that this whole patch stands on.
Thanks, Joey > -----Original Message----- > From: Nathan Sidwell [mailto:nathanmsidw...@gmail.com] On Behalf Of > Nathan Sidwell > Sent: 09 May 2016 15:07 > To: Richard Earnshaw; GCC Patches > Cc: Joey Ye > Subject: [ARM] mno-pic-data-is-text-relative & msingle-pic-base > > This patch comes from an off-list conversation between Joey & me. The > context is with RTOSs not all singing & dancing dynamic objects and OSes. > > currently, the documentation for -mno-pic-data-is-text-relative (-mno-PDITR) > says 'Assume that each data segments are relative to text segment at load > time. > Therefore, it permits addressing data using PC-relative operations. > This option is on by default for targets other than VxWorks RTP.' > > However, if you use just this option, you still end up with a pic-register > init > sequence that presumes a fixed mapping. That's a surprise. Joey tells me > its expected use is with -msingle-pic-base (-mSPB), which reserves a global > register to point at the (single) GOT. That's what I had expected the -mno- > PDITR option to have implied. > > Apparently there are legitimate reasons one might want the -mno-PDITR > behaviour without -mSPB. I don't know what those are, perhaps Joey could > clarify? > > Anyway, IMHO that is the rare case and the more common case is that one > would want to have -mnoPDITR imply -mSPB. (The reverse probably doesn't > apply.) > > This patch does 3 things. > 1) have -mno-PDITR imply -mSPB, unless one has explictly provided -m[no- > ]SPB. > 2) clarified the -m[no-]PDITR documentation. > 3) Added some testcases -- there didn't appear to be any. > > ok? > > nathan
