Build Failure on `riscv-linux-gnu-gcc-15` Because of Linking Error

Problem

When building with riscv-linux-gnu-gcc-15, the linking step fails with the following error:

error: PHDR segment not covered by LOAD segment

The makefile uses gcc for the final linking step:

CROSS_COMPILE ?= riscv64-unknown-linux-gnu-
CC = $(CROSS_COMPILE)gcc
LD = $(CROSS_COMPILE)gcc

When adding the --verbose flag to the linking step, part of the output shows:

 /usr/lib/gcc/riscv64-linux-gnu/15.1.0/collect2 -plugin /usr/lib/gcc/riscv64-linux-gnu/15.1.0/liblto_plugin.so -plugin-opt=/usr/lib/gcc/riscv64-linux-gnu/15.1.0/lto-wrapper -plugin-opt=-fresolution=/tmp/ccNDDJCY.res --sysroot=/usr/riscv64-linux-gnu --build-id --eh-frame-hdr --hash-style=gnu -melf64lriscv -X -dynamic-linker /lib/ld-linux-riscv64-lp64d.so.1 -pie -o build/gcpt -L/usr/lib/gcc/riscv64-linux-gnu/15.1.0 -L/usr/lib/gcc/riscv64-linux-gnu/15.1.0/../../../../riscv64-linux-gnu/lib -L/usr/riscv64-linux-gnu/lib -L/usr/riscv64-linux-gnu/usr/lib build/obj/src/boot.o build/obj/src/decode_restore.o build/obj/src/gcpt.o build/obj/src/gcpt_trap.o build/obj/src/printf.o build/obj/src/restore.o build/obj/src/trap.o build/obj/src/utils.o build/obj/resource/nanopb/pb_common.o build/obj/resource/nanopb/pb_decode.o build/obj/resource/nanopb/pb_encode.o build/obj/src/checkpoint.pb.o -T restore.lds
/usr/lib/gcc/riscv64-linux-gnu/15.1.0/../../../../riscv64-linux-gnu/bin/ld: build/gcpt: error: PHDR segment not covered by LOAD segment
/usr/lib/gcc/riscv64-linux-gnu/15.1.0/../../../../riscv64-linux-gnu/bin/ld: warning: build/gcpt has a LOAD segment with RWX permissions

The failure occurs because gcc adds unnecessary flags that prevent the files from linking correctly.

Impact of This Problem

This issue causes the CI flow of NEMU to fail in xs-env when using the configuration riscv64-xs-cpt-with-libcheckpoint_defconfig. This configuration depends on LibCheckpoint.

Suggested Fix

Use ld directly in the final linking step to gain explicit control over the linking behavior:

CROSS_COMPILE ?= riscv64-unknown-linux-gnu-
CC = $(CROSS_COMPILE)gcc
LD = $(CROSS_COMPILE)ld

This fix has been verified to work.

Start with the Makefile entries for CC, LD, and the final link command, then inspect restore.lds and the verbose linker output. Verify the change against the riscv64-xs-cpt-with-libcheckpoint_defconfig CI flow in xs-env; done means the configuration links without the PHDR error or RWX warning.