[PATCH] D67508: [RISCV] support mutilib in baremetal environment

Thu Oct 24 05:04:59 PDT 2019

lenary added a comment.

Ok, found a path forward for this patch. Notes inline:

================
Comment at: clang/lib/Driver/ToolChains/Gnu.cpp:1547
+  else if (IsRV64)
+    MArch = "rv64i";
+  else
----------------
khchen wrote:
> lenary wrote:
> > I think this line is the issue: where someone doesn't specify `-march`, you choose a default `-march` that does not appear in the list of multilib arches in `RISCVMultilibSet` above.
> > 
> > I think this issue probably didn't arise when you had `rv64i/lp64` in the list, but given that's not in the riscv-gcc `t-elf-multilib`, so this code should choose a new default. I don't know how this new default will affect defaults chosen in other parts of the clang codebase.
> oh it's why I added rv64i/lp64 in previous version, but it's wrong default.
> in riscv gcc if configure only with --enable-multilib, the default march/abi is rv64imafdc/lp64d
> The option 1 is aligning to gcc, but the default abi is lp64 in clang,
> maybe chosing rv64imac as default is less side effect? what do you think?
The solution for this patch is to use the function `riscv::getRISCVABI(const ArgList &Args, const llvm::Triple &Triple)` from `clang/lib/Driver/ToolChains/Arch/RISCV.h`. 

Then when I update the logic there to match gcc's logic, the right thing will happen. I will submit a patch to have this function match the gcc logic today. It took me a few hours but I found the default logic for GCC. 

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D67508/new/

https://reviews.llvm.org/D67508