On Fri, 17 Dec 2021, 07:49 Mathieu Malaterre, <malat@xxxxxxxxxx> wrote: > Hi all, > > I am staring at the following discussion, which eventually was resolved > with: > > * > https://github.com/riscv-collab/riscv-gcc/issues/12#issuecomment-276587351 > > Copied here for convenience (*). > > So if I understand the discussion correctly gcc is now adding by > default `--as-needed -latomic` for riscv arch to support c11/atomics. > What I fail to understand is why something identical was not applied > to powerpc/armel and mipsel ? > Probably because it was a decision by the risc-v target maintainers, who can decide what they want for their target, but not for other targets. > Typically on mipsel (Debian gcc 11.2.0 toolchain): > > % cat a.c > _Atomic(long long) ll; > > int main(void) > { > ++ll; > return 0; > } > > Result in: > > % gcc a.c > /usr/bin/ld: /tmp/ccsr7u8u.o: in function `main': > a.c:(.text+0x54): undefined reference to `__atomic_fetch_add_8' > /usr/bin/ld: a.c:(.text+0x5c): undefined reference to > `__atomic_fetch_add_8' > collect2: error: ld returned 1 exit status > > So currently, gcc wants the developer to add explicitly `--as-needed > -latomic` to the linker to get c11/atomics support. Would it make > sense to patch gcc so that `--as-needed -latomic` is added also for > those arches (powerpc, armel, mipsel...). > > Thanks for comments, > -M > > (*) > > diff --git a/gcc/config/riscv/linux.h b/gcc/config/riscv/linux.h > index d77ba3fcf27..1fab15fc081 100644 > --- a/gcc/config/riscv/linux.h > +++ b/gcc/config/riscv/linux.h > @@ -24,6 +24,12 @@ along with GCC; see the file COPYING3. If not see > > #define GLIBC_DYNAMIC_LINKER "/lib/ld-linux-riscv" XLEN_SPEC "-" > ABI_SPEC ".so.1" > > +/* Because RISC-V only has word-sized atomics, it requries libatomic where > + others do not. So link libatomic by default, as needed. */ > +#undef LIB_SPEC > +#define LIB_SPEC GNU_USER_TARGET_LIB_SPEC \ > + " " LD_AS_NEEDED_OPTION " -latomic " LD_NO_AS_NEEDED_OPTION \ > + > #define LINK_SPEC "\ > -melf" XLEN_SPEC "lriscv \ > %{shared} \ >
