https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119122
Bug ID: 119122
Summary: Zca does not imply C extension when it is possible
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: Yuriy.Kolerov at synopsys dot com
Target Milestone: ---
Target: riscv
GCC must imply C extension from Zca extension when it's possible. It's
necessary for achieving compatibility between different march strings which in
fact may be the same.
E.g., if rv32ic multilib configuration is presented in GCC, then GCC will not
choose this configuration for linking if -march=rv32i_zca is passed.
Here is a more practical example. From RISC-V Instruction Set Manual:
Therefore common ISA strings can be updated as follows to
include the relevant Zc extensions, for example:
- RV32IMC becomes RV32IM_Zce
- RV32IMCF becomes RV32IMF_Zce
With current implication rules this will not work well if rv32imc configuration
is presented and a user passes -march=rv32im_zce. This is how we can check this
with a simple empty test.c source file:
$ riscv64-unknown-elf-gcc -march=rv32ic -mabi=ilp32 -mriscv-attribute -S test.c
$ grep "attribute arch" test.s
.attribute arch, "rv32i2p1_c2p0_zca1p0"
$ riscv64-unknown-elf-gcc -march=rv32i_zce -mabi=ilp32 -mriscv-attribute -S
test.c
$ grep "attribute arch" test.s
.attribute arch,
"rv32i2p1_zicsr2p0_zca1p0_zcb1p0_zce1p0_zcmp1p0_zcmt1p0"
According to current GCC these march strings are incompatible: the first one
contains c2p0 and the second on doesn't.
GCC version, configuration and system type:
$ riscv64-unknown-elf-gcc --version
riscv64-unknown-elf-gcc (ga0d29dd218e) 15.0.1 20250301 (experimental)
$ riscv64-unknown-elf-gcc -v
Using built-in specs.
COLLECT_GCC=./install-old/bin/riscv64-unknown-elf-gcc
COLLECT_LTO_WRAPPER=/SCRATCH/ykolerov/workspace/arc-v/testing/gcc-zce/install-old/libexec/gcc/riscv64-unknown-elf/15.0.1/lto-wrapper
Target: riscv64-unknown-elf
Configured with:
/SCRATCH/ykolerov/workspace/arc-v/testing/gcc-zce/gcc/configure
--target=riscv64-unknown-elf
--prefix=/SCRATCH/ykolerov/workspace/arc-v/testing/gcc-zce/install-old
--disable-shared --disable-threads --enable-languages=c,c++
--with-pkgversion=ga0d29dd218e --with-system-zlib --enable-tls --with-newlib
--with-headers=/SCRATCH/ykolerov/workspace/arc-v/testing/gcc-zce/install-old/riscv64-unknown-elf/include
--disable-libmudflap --disable-libssp --disable-libquadmath --disable-libgomp
--disable-nls --disable-tm-clone-registry
--src=/SCRATCH/ykolerov/workspace/arc-v/testing/gcc-zce/gcc --enable-multilib
--with-multilib-generator='rv32i-ilp32--;rv32ic-ilp32--;rv32ifc-ilp32f--;rv32ifdc-ilp32d--;rv64i-lp64--;rv64ic-lp64--;rv64ifc-lp64f--;rv64ifdc-lp64d--'
--with-abi=lp64d --with-arch=rv64gc --with-tune=rocket --with-isa-spec=20191213
CFLAGS='-O0 -g' CXXFLAGS='-O0 -g' 'CFLAGS_FOR_TARGET=-Os -g '
'CXXFLAGS_FOR_TARGET=-Os -g '
Thread model: single
Supported LTO compression algorithms: zlib
gcc version 15.0.1 20250301 (experimental) (ga0d29dd218e)
$ uname -rvio
6.6.36.6-microsoft-standard-WSL2+ #1 SMP PREEMPT_DYNAMIC Thu Nov 28 17:58:07
+04 2024 x86_64 GNU/Linux
