diff --git a/local/docs/UPSTREAM-SYNC-PROCEDURE.md b/local/docs/UPSTREAM-SYNC-PROCEDURE.md
new file mode 100644
index 0000000000..fb31a4e3ae
--- /dev/null
+++ b/local/docs/UPSTREAM-SYNC-PROCEDURE.md
@@ -0,0 +1,375 @@
+# Upstream Sync Procedure for Local Forks
+
+**Created:** 2026-06-18
+**Scope:** relibc, kernel, bootloader, installer, redoxfs, userutils, base
+**Baseline:** Red Bear OS 0.1.0 (Redox snapshot)
+
+## Purpose
+
+Red Bear OS maintains local forks of core Redox components. Upstream Redox is
+actively developed and regularly merges refactoring, bug fixes, and new
+features. This document defines the **standard procedure** for updating each
+local fork to the latest upstream HEAD and re-applying Red Bear-specific
+changes on top.
+
+This is a **repeatable, per-package operation**. Every base system package
+must go through this process periodically to avoid accumulating fork drift.
+
+## When to Sync
+
+- A Rust nightly bump causes compile errors in the fork (unstable API changes).
+- Upstream adds features we were manually patching (eliminates a Red Bear patch).
+- Accumulated fork drift makes rebasing individual patches impractical.
+- Before a new Red Bear OS release.
+- When a bug in the fork is already fixed upstream.
+
+## Prerequisites
+
+```bash
+# Ensure upstream remote exists in the fork repo
+cd local/sources/<component>
+git remote -v
+# Should show: upstream -> https://gitlab.redox-os.org/redox-os/<component>.git
+
+# If missing:
+git remote add upstream https://gitlab.redox-os.org/redox-os/<component>.git
+```
+
+## Procedure
+
+### Step 1: Backup Current State
+
+**Never skip this.** The backup branch is your rollback point.
+
+```bash
+cd local/sources/<component>
+git fetch upstream --quiet
+
+# Create timestamped backup branch
+git branch backup-master-pre-upstream-update-$(date +%Y%m%d) master
+
+# Verify
+git log --oneline -1 backup-master-pre-upstream-update-*
+```
+
+### Step 2: Analyze Divergence
+
+Understand what you have vs what upstream has:
+
+```bash
+# Latest upstream HEAD
+git log --oneline upstream/master -3
+
+# Divergence point (merge-base)
+git merge-base master upstream/master
+
+# Your commits on top of upstream
+git log --oneline upstream/master..master
+
+# Files changed (scope assessment)
+git diff upstream/master..master --stat | tail -5
+```
+
+Categorize each commit:
+- **Feature port** — ported FROM upstream (e.g., posix_spawn). Upstream now
+  has it natively → **DROP**, use upstream's version.
+- **Red Bear feature** — unique to Red Bear (e.g., eventfd, signalfd, timerfd,
+  __fseterr, getprogname). Not in upstream → **KEEP**.
+- **Compatibility shim** — gnulib/glibc/musl compat (e.g., rpl_malloc,
+  __freadahead). → **KEEP** unless upstream added equivalent.
+- **Toolchain fix** — adapts to Rust nightly changes (e.g., unsafe blocks,
+  VaList API). → **CHECK** if still needed against current upstream.
+- **Revert/cleanup** — noise from previous iterations. → **DROP**.
+
+### Step 3: Create Sync Branch
+
+```bash
+# Branch from latest upstream
+git checkout -b redbear-upstream-sync-$(date +%Y%m%d) upstream/master
+```
+
+### Step 4: Squash-Merge Your Changes
+
+```bash
+# Squash-merge brings ALL your changes as staged, conflict-marked if needed
+git merge --squash master
+```
+
+If untracked files block the merge (files that exist in your fork but not
+upstream, left over from failed attempts):
+
+```bash
+git merge --abort
+git reset --hard upstream/master
+git clean -fd
+git merge --squash master
+```
+
+### Step 5: Resolve Conflicts
+
+This is the most time-consuming step. For each conflicted file:
+
+```bash
+# List conflicts
+git diff --name-only --diff-filter=U
+```
+
+**Resolution strategy per file:**
+
+| Conflict Type | Resolution |
+|---|---|
+| Add/Add (both added same file) | Check which is canonical. If upstream now has it (e.g., spawn), take upstream: `git checkout --ours <file>` |
+| Feature you ported from upstream | Take upstream: `git checkout --ours <file>` |
+| Red Bear unique feature | Take ours: `git checkout --theirs <file>` |
+| Both sides modified same code | **Manual merge** — keep both sets of changes |
+| Cargo.toml/Cargo.lock | Resolve Cargo.toml manually, regenerate Cargo.lock with `cargo update` |
+
+```bash
+# Take upstream (current branch = upstream):
+git checkout --ours <file> && git add <file>
+
+# Take ours (the merged branch = our fork):
+git checkout --theirs <file> && git add <file>
+
+# Manual resolution:
+# Edit file, remove conflict markers, keep both sides' relevant changes
+git add <file>
+```
+
+**Conflict count expectation:**
+- relibc: 5-15 conflict files (heavy upstream refactoring)
+- kernel: 10-30 conflict files
+- base: 5-10 conflict files
+- Others: 2-5 conflict files
+
+### Step 6: Commit the Squash
+
+```bash
+git commit -m "sync: upstream <component> to $(git rev-parse --short upstream/master)
+
+Re-applied Red Bear-specific changes on top of latest upstream.
+Dropped commits for features now in upstream.
+Backup: backup-master-pre-upstream-update-$(date +%Y%m%d)"
+```
+
+### Step 7: Compile Test
+
+```bash
+# Build the component via the cookbook
+cd /home/kellito/Builds/RedBear-OS
+rm -rf recipes/core/<component>/source recipes/core/<component>/target
+export CI=1 COOKBOOK_OFFLINE=false REDBEAR_ALLOW_PROTECTED_FETCH=1
+./target/release/repo cook recipes/core/<component>
+```
+
+Fix any compile errors. These are usually:
+- **Unsafe block changes** (Rust 2024 edition) — wrap in `unsafe { }`.
+- **API renames** — upstream renamed a function/type.
+- **Module path changes** — upstream reorganized headers.
+- **Trait signature changes** — upstream changed a trait method signature.
+
+### Step 8: Verify Functionality
+
+For relibc specifically:
+```bash
+# Check critical symbols are present
+nm recipes/core/relibc/target/x86_64-unknown-redox/stage/x86_64-unknown-redox/lib/libc.a | \
+  grep -E "__fseterr|eventfd|signalfd|timerfd|open_memstream"
+
+# Check static libs exist
+ls -la recipes/core/relibc/target/x86_64-unknown-redox/stage/x86_64-unknown-redox/lib/*.a
+```
+
+### Step 9: Push to Gitea
+
+```bash
+cd local/sources/<component>
+# Switch sync branch to master (or merge sync into master)
+git checkout master
+git reset --hard redbear-upstream-sync-$(date +%Y%m%d)
+git push gitea master --force-with-lease
+```
+
+### Step 10: Update Recipe
+
+If the recipe uses `git + patches` (not `path`):
+```bash
+# Update the pinned rev in recipe.toml to match new HEAD
+# Remove patches that are now in upstream
+```
+
+If the recipe uses `path` (local fork):
+```bash
+# No recipe changes needed — the fork IS the source
+```
+
+### Step 11: Rebuild Dependent Components
+
+After updating a base component, everything that depends on it must rebuild:
+
+| Component Updated | Must Rebuild |
+|---|---|
+| relibc | prefix, then ALL C recipes (bison, flex, m4, etc.) |
+| kernel | base, drivers, all recipes |
+| base | everything in the image |
+| bootloader | disk image creation |
+| installer | disk image creation |
+| redoxfs | disk image creation |
+| userutils | base, login/session recipes |
+
+### Step 12: Full Image Build
+
+```bash
+cd /home/kellito/Builds/RedBear-OS
+pkill -9 -f "build-redbear\|repo cook"
+rm -rf recipes/core/<component>/source recipes/core/<component>/target
+
+export CI=1 REDBEAR_ALLOW_PROTECTED_FETCH=1
+setsid nohup env CI=1 REDBEAR_ALLOW_PROTECTED_FETCH=1 \
+  ./local/scripts/build-redbear.sh --upstream redbear-mini \
+  > /tmp/build-V<N>.log 2>&1 < /dev/null &
+```
+
+## Package-Specific Notes
+
+### relibc
+
+- **Upstream repo:** `https://gitlab.redox-os.org/redox-os/relibc.git`
+- **Fork location:** `local/sources/relibc/`
+- **Recipe:** `recipes/core/relibc/recipe.toml`
+- **Red Bear features to preserve:**
+  - `eventfd` (eventfd_create, eventfd_read, eventfd_write)
+  - `signalfd` (signalfd_create/signalfd)
+  - `timerfd` (timerfd_create, timerfd_settime, timerfd_gettime)
+  - `__fseterr`, `__freadahead` (gnulib/m4/bison compatibility)
+  - `getprogname` (via `sys:exe` scheme)
+  - `getloadavg` (via `/proc/loadavg`)
+  - `clock_settime` (proper implementation)
+  - `getifaddrs`, `if_nameindex` (networking)
+  - `getrlimit`, `getrusage` (resource limits)
+  - `waitid` (POSIX waitid)
+  - `dup3`, `F_DUPFD_CLOEXEC` fallback
+  - `secure_getenv`, `getentropy`
+  - `clock_nanosleep`
+  - POSIX semaphores (`sem_open`/`sem_close`/`sem_unlink`)
+  - POSIX mqueue (`mq_*`)
+  - `DT_RPATH` support in ld.so
+  - `redox_syscall = "0.8.1"` (ABI migration)
+  - DRM ioctl definitions (GET_UNIQUE, SET_VERSION, MODE_ADD_FB2)
+  - `rpl_malloc`/`rpl_realloc` (gnulib compat)
+  - 8MB stack size
+- **Features now in upstream (DROP from Red Bear):**
+  - `posix_spawn` (port from upstream → upstream now has it)
+  - VaList API adaptation (upstream fixed)
+  - Various doc/lint fixes (upstream applied)
+- **Compile gotchas:**
+  - `core::arch::x86_64::__cpuid()` requires `unsafe { }` block (edition 2024)
+  - `Vec::into_raw_parts()` is unstable — use `mem::transmute` + `as_ptr`/`len`/`capacity`
+  - `-D unused_mut` in upstream Makefile flags
+
+### kernel
+
+- **Upstream repo:** `https://gitlab.redox-os.org/redox-os/kernel.git`
+- **Fork location:** `local/sources/kernel/`
+- **Red Bear features to preserve:**
+  - Any ACPI improvements specific to AMD
+  - IRQ routing changes
+  - MSI/MSI-X support
+  - IOMMU work
+- **Check upstream first** — kernel is the fastest-moving Redox component
+
+### bootloader
+
+- **Upstream repo:** `https://gitlab.redox-os.org/redox-os/bootloader.git`
+- **Fork location:** `local/sources/bootloader/`
+- **Red Bear features to preserve:**
+  - Branding (Red Bear logo, colors)
+  - Any boot protocol changes
+
+### installer
+
+- **Upstream repo:** `https://gitlab.redox-os.org/redox-os/installer.git`
+- **Fork location:** `local/sources/installer/`
+- **Red Bear features to preserve:**
+  - ext4 filesystem support
+  - GRUB bootloader support
+  - CollisionTracker (file ownership conflict detection)
+  - Init service path validation
+
+### redoxfs
+
+- **Upstream repo:** `https://gitlab.redox-os.org/redox-os/redoxfs.git`
+- **Fork location:** `local/sources/redoxfs/`
+- **Red Bear features to preserve:**
+  - Any performance patches
+  - Any filesystem format changes
+
+### userutils
+
+- **Upstream repo:** `https://gitlab.redox-os.org/redox-os/userutils.git`
+- **Fork location:** `local/sources/userutils/`
+- **Red Bear features to preserve:**
+  - Custom `/etc/issue` (Red Bear login banner)
+  - Any Redox ABI changes for syscall 0.8.x
+
+### base
+
+- **Upstream repo:** Pinned via `recipes/core/base/recipe.toml` (path-based fork)
+- **Fork location:** `local/sources/base/`
+- **Red Bear features to preserve:**
+  - All Red Bear init.d services
+  - All Red Bear branding
+  - All Red Bear config overrides
+  - HID/I2C driver wiring
+  - D-Bus integration
+  - Session management (redbear-sessiond)
+  - ~100 individual P*.patch files in `local/patches/base/`
+
+## Rollback Procedure
+
+If the sync fails or produces a broken build:
+
+```bash
+cd local/sources/<component>
+git checkout master
+git reset --hard backup-master-pre-upstream-update-<date>
+git push gitea master --force-with-lease
+```
+
+Then in the main repo:
+```bash
+git checkout -- recipes/core/<component>/recipe.toml
+# Revert recipe changes if any
+```
+
+## Decision Matrix: Keep vs Drop vs Merge
+
+For each Red Bear commit when syncing:
+
+```
+Is the feature in upstream now?
+├── YES → Does upstream's version work for us?
+│   ├── YES → DROP our commit, use upstream
+│   └── NO  → MERGE: take upstream's structure, re-apply our specific changes
+└── NO  → Is it a Red Bear unique feature?
+    ├── YES → KEEP our commit
+    └── NO  → Is it a toolchain/compat fix?
+        ├── Still needed? → KEEP
+        └── Fixed upstream? → DROP
+```
+
+## Checklist Per Package
+
+- [ ] Backup branch created
+- [ ] Divergence analyzed (commits categorized)
+- [ ] Sync branch created from latest upstream
+- [ ] Squash-merge applied
+- [ ] All conflicts resolved
+- [ ] Commit made with sync message
+- [ ] Compiles via `repo cook`
+- [ ] Critical symbols verified (for relibc)
+- [ ] Pushed to Gitea
+- [ ] Recipe updated (if git+patches mode)
+- [ ] Dependent components rebuilt
+- [ ] Full image build succeeds
+- [ ] QEMU boot test passes
diff --git a/mk/prefix.mk b/mk/prefix.mk
index 313a372775..40bd702f60 100644
--- a/mk/prefix.mk
+++ b/mk/prefix.mk
@@ -97,6 +97,16 @@ ifeq ($(PODMAN_BUILD),1)
 else
 	rm -rf "$@"
 	cp -r "$(PREFIX)/relibc-install/" "$@"
+# Propagate fresh relibc artifacts (libc.a, crt*.o, headers) from the
+# rebuilt sysroot back into gcc-install.  The GCC driver's built-in
+# library search path always looks inside gcc-install/ first; if that
+# copy is stale (from the original GCC bootstrap) the linker silently
+# picks up an outdated libc.a and we get spurious undefined-reference
+# errors for symbols that exist only in the new relibc (e.g. __fseterr,
+# __freadahead, eventfd helpers, …).  This sync guarantees that every
+# libc.a copy in the toolchain is identical to the one just compiled.
+	cp -rf "$@/$(GNU_TARGET)/lib/"* "$(PREFIX)/gcc-install/$(GNU_TARGET)/lib/"
+	cp -rf "$@/$(GNU_TARGET)/include/"* "$(PREFIX)/gcc-install/$(GNU_TARGET)/include/"
 # adapt path for libtoolize
 	sed 's|/usr/share|$(ROOT)/$@/share|g' "$@/bin/libtoolize.orig" > "$@/bin/libtoolize"
 	chmod 0755 "$@/bin/libtoolize"
diff --git a/recipes/core/relibc/recipe.toml b/recipes/core/relibc/recipe.toml
index 5829bb7678..aca0b76cda 100644
--- a/recipes/core/relibc/recipe.toml
+++ b/recipes/core/relibc/recipe.toml
@@ -1,74 +1,5 @@
 [source]
-git = "https://gitlab.redox-os.org/redox-os/relibc.git"
-rev = "861bbb0"
-patches = [
-    # Bump relibc workspace redox_syscall pin to 0.8.1 (matches rest of build)
-    "P0-relibc-syscall-0.8.1.patch",
-    # Bump redox-ioctl's redox_syscall pin to 0.8.1 (matches rest of build)
-    "P3-eventfd-mod.patch",
-    # Add pub mod bits_eventfd to header/mod.rs
-    "P3-bits-eventfd-mod.patch",
-    # bits_eventfd module (eventfd_t type)
-    "P3-bits-eventfd.patch",
-    # sys_eventfd module — FULL eventfd() implementation (opens /scheme/event/eventfd)
-    "P3-eventfd-impl.patch",
-    # cbindgen.toml for sys/eventfd.h C header generation
-    "P3-eventfd-cbindgen.patch",
-    # eventfd_read() and eventfd_write() helpers
-    "P3-eventfd-readwrite.patch",
-    # sys_signalfd module (cbindgen.toml + mod.rs with cbindgen exports)
-    "P3-signalfd-header.patch",
-    # signalfd implementation (signal/signalfd.rs + signal/mod.rs wiring)
-    "P3-signalfd.patch",
-    # sys_timerfd module (creates mod.rs with timerfd_create/settime/gettime)
-    "P3-timerfd-impl.patch",
-    # timerfd: creates cbindgen.toml, reformats, adds relative time handling
-    "P3-timerfd-relative.patch",
-    # timerfd: fix cbindgen.toml to generate C (not C++) headers
-    "P3-timerfd-cbindgen-fix.patch",
-
-    # sys_types_internal: include stdint.h so uint32_t/int32_t are available to
-    # all downstream headers (signal.h, sys_signalfd.h, etc.) via the
-    # signal.h -> sys/types.h -> sys/types/internal.h include chain
-    "P3-sys-types-stdint-include.patch",
-
-    # open_memstream: creates stdio/open_memstream.rs
-    "P3-open-memstream-create.patch",
-    # open_memstream: wires mod into stdio/mod.rs
-    "P3-stdio-open-memstream-mod.patch",
-    # F_DUPFD_CLOEXEC fallback (try CLOEXEC, fall back to DUPFD + SETFD)
-    "P3-fcntl-dupfd-cloexec.patch",
-    # Non-conflicting individual patches
-    "P3-elf64-types.patch",
-    "P3-clock-nanosleep.patch",
-    "P3-exec-root-bypass.patch",
-    "P3-secure-getenv.patch",
-    "P3-getentropy.patch",
-    "P3-dup3.patch",
-    "P3-waitid-header.patch",
-    "P3-waitid.patch",
-    "P3-in6-pktinfo.patch",
-    "P3-inet6-pton-ntop.patch",
-    "P3-tcp-nodelay.patch",
-    "P3-tcp-sockopt-forward.patch",
-    # Named POSIX semaphores (sem_open/close/unlink) — comprehensive + refcount + va_list
-    "P3-semaphore-comprehensive.patch",
-    # semaphore.h: expose SEM_FAILED and real variadic sem_open() prototype/ABI
-    "P3-semaphore-varargs-header.patch",
-    # Reverse From<&syscall::TimeSpec> for timespec (needed by getrusage)
-    "P3-timespec-reverse-from.patch",
-    "P10-stack-size-8mb.patch",
-    "P11-getrlimit-getrusage.patch",
-    # Move #include <stdint.h> after size_t/ptrdiff_t typedefs in stddef.h
-    # to prevent recursive include chain (stdint.h → sys/types.h → pthread.h)
-    # from seeing undefined size_t when gnulib wrappers are present
-    "P3-stddef-reorder.patch",
-    # ld.so: parse DT_RPATH in addition to DT_RUNPATH (RUNPATH takes precedence per gABI)
-    "P3-ldso-rpath-support.patch",
-
-    # stdio_ext.h + __freadahead / __fseterr (m4/bison/flex gnulib compatibility)
-    "P3-stdio-fseterr.patch",
-]
+path = "../../../local/sources/relibc"
 
 [build]
 template = "custom"
diff --git a/src/config.rs b/src/config.rs
index 0b4d9d6e02..cb79f58802 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -104,33 +104,44 @@ pub fn init_config() {
                 .unwrap_or(1),
         ));
     }
-    if config.cook_opt.logs.is_none() {
-        config.cook_opt.logs = Some(extract_env("COOKBOOK_LOGS", config.cook_opt.tui.unwrap()));
-    }
-    if config.cook_opt.offline.is_none() {
-        config.cook_opt.offline = Some(extract_env("COOKBOOK_OFFLINE", true));
-    }
-    if config.cook_opt.compressed.is_none() {
-        config.cook_opt.compressed = Some(extract_env("COOKBOOK_COMPRESSED", false));
-    }
-    if config.cook_opt.verbose.is_none() {
-        config.cook_opt.verbose = Some(extract_env("COOKBOOK_VERBOSE", true));
-    }
-    if config.cook_opt.nonstop.is_none() {
-        config.cook_opt.nonstop = Some(extract_env("COOKBOOK_NONSTOP", false));
-    }
-    if config.cook_opt.clean_build.is_none() {
-        config.cook_opt.clean_build = Some(extract_env("COOKBOOK_CLEAN_BUILD", false));
-    }
-    if config.cook_opt.clean_target.is_none() {
-        config.cook_opt.clean_target = Some(extract_env("COOKBOOK_CLEAN_TARGET", false));
-    }
-    if config.cook_opt.write_filetree.is_none() {
-        config.cook_opt.write_filetree = Some(extract_env(
-            "COOKBOOK_WRITE_FILETREE",
+    // --- Env-var override layer ---
+    // Environment variables ALWAYS override cookbook.toml values.  The TOML
+    // value (or a sensible default) is used only when the env var is absent.
+    // This follows the standard "env > config-file > built-in-default" hierarchy.
+    config.cook_opt.logs = Some(extract_env(
+        "COOKBOOK_LOGS",
+        config.cook_opt.logs.unwrap_or(config.cook_opt.tui.unwrap()),
+    ));
+    config.cook_opt.offline = Some(extract_env(
+        "COOKBOOK_OFFLINE",
+        config.cook_opt.offline.unwrap_or(true),
+    ));
+    config.cook_opt.compressed = Some(extract_env(
+        "COOKBOOK_COMPRESSED",
+        config.cook_opt.compressed.unwrap_or(false),
+    ));
+    config.cook_opt.verbose = Some(extract_env(
+        "COOKBOOK_VERBOSE",
+        config.cook_opt.verbose.unwrap_or(true),
+    ));
+    config.cook_opt.nonstop = Some(extract_env(
+        "COOKBOOK_NONSTOP",
+        config.cook_opt.nonstop.unwrap_or(false),
+    ));
+    config.cook_opt.clean_build = Some(extract_env(
+        "COOKBOOK_CLEAN_BUILD",
+        config.cook_opt.clean_build.unwrap_or(false),
+    ));
+    config.cook_opt.clean_target = Some(extract_env(
+        "COOKBOOK_CLEAN_TARGET",
+        config.cook_opt.clean_target.unwrap_or(false),
+    ));
+    config.cook_opt.write_filetree = Some(extract_env(
+        "COOKBOOK_WRITE_FILETREE",
+        config.cook_opt.write_filetree.unwrap_or(
             config.cook_opt.clean_target.unwrap_or(false) || extract_env("COOKBOOK_WEB", false),
-        ));
-    }
+        ),
+    ));
     if config.mirrors.len() == 0 {
         // The GNU FTP mirror below is automatically inserted for convenience
         // You can choose other mirrors by setting it on cookbook.toml
diff --git a/src/cook/script.rs b/src/cook/script.rs
index ad79294f42..fce6894375 100644
--- a/src/cook/script.rs
+++ b/src/cook/script.rs
@@ -35,6 +35,14 @@ function DYNAMIC_INIT {
 
     # TODO: check paths for spaces
     export LDFLAGS="${USER_LDFLAGS}-Wl,-rpath-link,${COOKBOOK_SYSROOT}/lib -L${COOKBOOK_SYSROOT}/lib"
+
+    # Re-add prefix toolchain sysroot libs for dynamic builds.
+    # DYNAMIC_INIT resets LDFLAGS from USER_LDFLAGS, so the -L added by
+    # BUILD_PRESCRIPT is lost.  Add it back here.
+    REDBEAR_PREFIX_SYSROOT="${COOKBOOK_ROOT}/prefix/${TARGET}/sysroot"
+    if [ -d "${REDBEAR_PREFIX_SYSROOT}/${TARGET}/lib" ]; then
+        export LDFLAGS="${LDFLAGS} -L${REDBEAR_PREFIX_SYSROOT}/${TARGET}/lib"
+    fi
     export RUSTFLAGS="-C target-feature=-crt-static -L native=${COOKBOOK_SYSROOT}/lib -C link-arg=-Wl,-rpath-link,${COOKBOOK_SYSROOT}/lib"
     export COOKBOOK_DYNAMIC=1
 
@@ -106,6 +114,15 @@ export CPPFLAGS="${CPPFLAGS:+$CPPFLAGS }-I${COOKBOOK_SYSROOT}/include"
 USER_LDFLAGS="${LDFLAGS:+$LDFLAGS }"
 export LDFLAGS="${USER_LDFLAGS}-L${COOKBOOK_SYSROOT}/lib --static"
 
+# Belt-and-suspenders: explicitly add the prefix toolchain sysroot to the
+# linker search path so the fresh relibc libc.a is always found, regardless
+# of which GCC binary the redoxer ends up invoking.  See the companion sync
+# step in mk/prefix.mk ($(PREFIX)/sysroot target) for the full explanation.
+REDBEAR_PREFIX_SYSROOT="${COOKBOOK_ROOT}/prefix/${TARGET}/sysroot"
+if [ -d "${REDBEAR_PREFIX_SYSROOT}/${TARGET}/lib" ]; then
+    export LDFLAGS="${LDFLAGS} -L${REDBEAR_PREFIX_SYSROOT}/${TARGET}/lib"
+fi
+
 # This reexport C variables into custom build script that can be consumed by cc crate
 function reexport_flags {
     target=${TARGET//-/_}