diff --git a/setup_tools.sh b/setup_tools.sh
index 65c1b64..5b56c5b 100755
--- a/setup_tools.sh
+++ b/setup_tools.sh
@@ -18,9 +18,9 @@ JDK_SHA256="d8afc263758141a66e0e3aafc321e783f7016696f4eaea067d340a269037d331"
 MILL_URL="https://github.com/com-lihaoyi/mill/releases/download/$MILL_VERSION/$MILL_VERSION"
 MILL_SHA256="ebe83649cd63acd33608f6d14452c074be2ed7d00cd2f69f88573d3f6909774f"
 
-CIRCT_ARCHIVE="circt-full-shared-linux-x64.tar.gz"
+CIRCT_ARCHIVE="firrtl-bin-linux-x64.tar.gz"
 CIRCT_URL="https://github.com/llvm/circt/releases/download/firtool-$FIRTOOL_VERSION/$CIRCT_ARCHIVE"
-CIRCT_SHA256="dde442dcd0ada92e6f7db26f4744667471f7be61d10f2876297efb435fc9a5ec"
+CIRCT_SHA256="10bf9b135a65e5d93fb0555e967eac4258400ee629731ba68a69be6b7f9781ce"
 
 Z3_ARCHIVE="z3-$Z3_VERSION-x64-glibc-2.39.zip"
 Z3_URL="https://github.com/Z3Prover/z3/releases/download/z3-$Z3_VERSION/$Z3_ARCHIVE"
@@ -85,7 +85,8 @@ if [[ ! -x "$TOOLS_ROOT/mill/$MILL_VERSION/mill" ]]; then
   "${SUDO[@]}" install -m 0755 "$work_dir/mill" "$TOOLS_ROOT/mill/$MILL_VERSION/mill"
 fi
 
-if [[ ! -x "$TOOLS_ROOT/circt/firtool-$FIRTOOL_VERSION/bin/firtool" ]]; then
+if ! "$TOOLS_ROOT/circt/firtool-$FIRTOOL_VERSION/bin/firtool" --version \
+    >/dev/null 2>&1; then
   download "$CIRCT_URL" "$work_dir/$CIRCT_ARCHIVE" "$CIRCT_SHA256"
   mkdir -p "$work_dir/circt"
   tar -xzf "$work_dir/$CIRCT_ARCHIVE" -C "$work_dir/circt"
diff --git a/source.sh b/source.sh
index 2f5ea73..9c4318f 100755
--- a/source.sh
+++ b/source.sh
@@ -29,17 +29,17 @@ done
 export Z3_LIB_DIR="${Z3_LIB_DIR:-$_gps_z3_dir}"
 
 _gps_riscv_gcc=""
-if [[ -n "${TOOLCHAIN:-}" ]]; then
-  _gps_candidates=("$TOOLCHAIN")
-elif [[ -n "${RISCV_TOOLCHAIN:-}" ]]; then
+if [[ -n "${RISCV_TOOLCHAIN:-}" ]]; then
   _gps_candidates=("$RISCV_TOOLCHAIN" "$RISCV_TOOLCHAIN/bin")
+elif [[ -n "${TOOLCHAIN:-}" ]]; then
+  _gps_candidates=("$TOOLCHAIN")
 else
   _gps_candidates=(
     "$GPS_ROOT/tools/local/riscv/bin"
     /tools/toolchains-medany/bin
+    /tools/toolchains/rvtc-medany/bin
     /tools/toolchain/bin
     /tools/toolchains/bin
-    /tools/toolchains/rvtc-medany/bin
   )
 fi
 
diff --git a/tools/doctor.sh b/tools/doctor.sh
index f53eb39..36863d0 100755
--- a/tools/doctor.sh
+++ b/tools/doctor.sh
@@ -30,6 +30,27 @@ if [[ -n "$TOOLCHAIN" ]]; then
 fi
 check riscv-gcc "$riscv_gcc" --version
 
+if [[ -n "$riscv_gcc" && -x "$riscv_gcc" ]]; then
+  medany_dir="$(mktemp -d "${TMPDIR:-/tmp}/gps-medany-check.XXXXXXXX")"
+  printf '%s\n' \
+    '#include <stdlib.h>' \
+    'void _start(void) { void *p = malloc(16); free(p); for (;;) {} }' \
+    > "$medany_dir/check.c"
+  if "$riscv_gcc" \
+      -march=rv64imafdc_zicsr_zifencei -mabi=lp64d -mcmodel=medany \
+      -Os -ffreestanding -fno-builtin -static -nostartfiles \
+      -Wl,-Ttext=0x80000000 -Wl,--unresolved-symbols=ignore-all \
+      "$medany_dir/check.c" -Wl,--start-group -lc -lgcc -Wl,--end-group \
+      -o "$medany_dir/check.elf" >/dev/null 2>&1; then
+    printf 'OK       %-10s %s\n' riscv-libc 'medany @ 0x80000000'
+  else
+    printf 'INCOMPAT %-10s %s\n' riscv-libc \
+      'libc is not medany; select RISCV_TOOLCHAIN=/tools/toolchains/rvtc-medany'
+    status=1
+  fi
+  rm -rf "$medany_dir"
+fi
+
 if [[ "$(uname -s)" != Linux || "$(uname -m)" != x86_64 ]]; then
   printf 'WARNING  Kilitli JDK/CIRCT paketleri Linux-x86_64 icindir.\n'
 fi
diff --git a/tools/project.mk b/tools/project.mk
index 13edd8b..d80222a 100644
--- a/tools/project.mk
+++ b/tools/project.mk
@@ -21,23 +21,32 @@ VIVADO ?= $(lastword $(sort $(wildcard /tools/Xilinx/*/Vivado/bin/vivado) $(shel
 # TOOLCHAIN keeps compatibility with the existing software Makefiles.
 RISCV_TOOLCHAIN ?=
 _RISCV_SEARCH_DIRS := \
+  $(if $(strip $(RISCV_TOOLCHAIN)),$(RISCV_TOOLCHAIN) $(RISCV_TOOLCHAIN)/bin) \
   $(TOOLCHAIN) \
-  $(RISCV_TOOLCHAIN) \
-  $(RISCV_TOOLCHAIN)/bin \
   $(PROJECT_TOOLS_DIR)/riscv/bin \
   /tools/toolchains-medany/bin \
+  /tools/toolchains/rvtc-medany/bin \
   /tools/toolchain/bin \
-  /tools/toolchains/bin \
-  /tools/toolchains/rvtc-medany/bin
+  /tools/toolchains/bin
 _RISCV_GCC := $(firstword \
   $(foreach d,$(_RISCV_SEARCH_DIRS),$(wildcard $(d)/riscv64-unknown-elf-gcc)) \
   $(foreach d,$(_RISCV_SEARCH_DIRS),$(wildcard $(d)/riscv64-none-elf-gcc)) \
   $(shell command -v riscv64-unknown-elf-gcc 2>/dev/null) \
   $(shell command -v riscv64-none-elf-gcc 2>/dev/null))
 
+# An explicit RISCV_TOOLCHAIN is authoritative, including over an old
+# TOOLCHAIN/RISCV_PREFIX inherited from the shell.  Without override, Make's
+# environment-variable semantics leave CROSS pointing at the stale toolchain
+# even though _RISCV_GCC was found in RISCV_TOOLCHAIN.
+ifneq ($(strip $(RISCV_TOOLCHAIN)),)
+override TOOLCHAIN := $(patsubst %/,%,$(dir $(_RISCV_GCC)))
+override RISCV_PREFIX := $(if $(_RISCV_GCC),$(patsubst %-gcc,%-,$(notdir $(_RISCV_GCC))),riscv64-unknown-elf-)
+override CROSS := $(if $(strip $(TOOLCHAIN)),$(TOOLCHAIN)/)$(RISCV_PREFIX)
+else
 TOOLCHAIN ?= $(patsubst %/,%,$(dir $(_RISCV_GCC)))
 RISCV_PREFIX ?= $(if $(_RISCV_GCC),$(patsubst %-gcc,%-,$(notdir $(_RISCV_GCC))),riscv64-unknown-elf-)
 CROSS ?= $(if $(strip $(TOOLCHAIN)),$(TOOLCHAIN)/)$(RISCV_PREFIX)
+endif
 
 # Some compiler-only toolchains (notably rvtc-medany) do not ship GDB.  Keep
 # using the selected compiler toolchain, but fall back to the full local
@@ -45,6 +54,8 @@ CROSS ?= $(if $(strip $(TOOLCHAIN)),$(TOOLCHAIN)/)$(RISCV_PREFIX)
 _RISCV_GDB := $(firstword \
   $(wildcard $(TOOLCHAIN)/$(RISCV_PREFIX)gdb) \
   $(wildcard /tools/toolchains/tc/toolchain/bin/$(RISCV_PREFIX)gdb) \
+  $(wildcard /tools/toolchain/bin/$(RISCV_PREFIX)gdb) \
+  $(lastword $(sort $(wildcard /tools/Xilinx/*/gnu/riscv/lin/bin/$(RISCV_PREFIX)gdb))) \
   $(shell command -v $(RISCV_PREFIX)gdb 2>/dev/null))
 GDB ?= $(if $(_RISCV_GDB),$(_RISCV_GDB),$(CROSS)gdb)