build: stop rm -rf'ing a RandomX tree the build did not create

deps-randomx built into $(HOME)/RandomX and deleted that path whenever
the library was missing, taking out hand-managed checkouts the build
never owned. Default the build to the in-tree $(ROOT)/randomx-build,
like secp256k1-build, overridable via RANDOMX_DIR and exported so
src/Makefile's own fallback resolves to the same tree. As a backstop,
the recipe writes a .bitflash-built marker after a successful build and
refuses to delete any directory that lacks it, so a user-supplied
RANDOMX_DIR pointing at a pre-existing tree is never removed.

Closes #27

2 files changed, 27 insertions, 8 deletions

diff --git a/Makefile b/Makefile
index 9f97b73..83a2c73 100644
--- a/Makefile
+++ b/Makefile
@@ -59,6 +59,17 @@ APPIMAGETOOL_SHA256 := ed4ce84f0d9caff66f50bcca6ff6f35aae54ce8135408b3fa33abfc3c
 
 # ---- Linux ----------------------------------------------------------------
 
+# RandomX used to build in $(HOME)/RandomX, and deps-randomx would rm -rf that
+# path whenever the library was missing -- deleting a tree the build did not
+# create and does not own (issue #27; a hand-managed pinned checkout there is
+# what this machine's miners build against). The default is now in-tree, like
+# secp256k1-build. A host that deliberately keeps RandomX elsewhere can set
+# RANDOMX_DIR=... explicitly; the recipe below will still never delete a
+# directory that lacks the marker file this build writes after a successful
+# build. Exported so src/Makefile's own RANDOMX_DIR ?= picks the same tree.
+RANDOMX_DIR ?= $(ROOT)/randomx-build
+export RANDOMX_DIR
+
 linux: deps-linux
         $(MAKE) -C src -f Makefile -j$(NPROC)
         strip src/bitflash
@@ -109,19 +120,25 @@ deps-secp256k1:
         fi
 
 deps-randomx:
-        @if [ ! -f $(HOME)/RandomX/build/librandomx.a ]; then \
+        @if [ ! -f $(RANDOMX_DIR)/build/librandomx.a ]; then \
+          if [ -d $(RANDOMX_DIR) ] && [ ! -f $(RANDOMX_DIR)/.bitflash-built ]; then \
+            echo "ERROR: $(RANDOMX_DIR) exists but was not created by this build"; \
+            echo "       refusing to rm -rf it -- remove it yourself or set RANDOMX_DIR"; \
+            exit 1; \
+          fi; \
           echo "==> building RandomX"; \
-          rm -rf $(HOME)/RandomX; \
-          git init -q $(HOME)/RandomX; \
-          cd $(HOME)/RandomX && \
+          rm -rf $(RANDOMX_DIR); \
+          git init -q $(RANDOMX_DIR); \
+          cd $(RANDOMX_DIR) && \
           git remote add origin $(RANDOMX_REPO) && \
           git fetch -q --depth 1 origin $(RANDOMX_COMMIT) && \
           git checkout -q --detach FETCH_HEAD && \
           test "$$(git rev-parse HEAD)" = "$(RANDOMX_COMMIT)" && \
           echo "==> RandomX pinned at $(RANDOMX_COMMIT)" && \
-          mkdir -p $(HOME)/RandomX/build; \
-          cd $(HOME)/RandomX/build && cmake .. -DCMAKE_BUILD_TYPE=Release && \
-          make -j$(NPROC) randomx; \
+          mkdir -p $(RANDOMX_DIR)/build && \
+          cd $(RANDOMX_DIR)/build && cmake .. -DCMAKE_BUILD_TYPE=Release && \
+          make -j$(NPROC) randomx && \
+          touch $(RANDOMX_DIR)/.bitflash-built && \
           echo "==> RandomX done"; \
         else \
           echo "==> RandomX already built"; \
diff --git a/src/Makefile b/src/Makefile
index 1bc3ae8..2c6d304 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -6,7 +6,9 @@ FUZZ_CXX ?= clang++
 
 SECP_INC    ?= /usr/local/include
 SECP_LIB    ?= /usr/local/lib
-RANDOMX_DIR ?= $(HOME)/RandomX
+# The root Makefile exports RANDOMX_DIR (default: <repo>/randomx-build, built
+# by deps-randomx). This fallback only applies when src/ is built standalone.
+RANDOMX_DIR ?= $(abspath $(CURDIR)/..)/randomx-build
 
 IMGUI_DIR = imgui