DF-5474 — vkernel64 platform does not build: kern_mib __build_id_* unresolved (SYSTEM_LD drops ELDFLAGS and never uses the platform ldscript)

File: sys/platform/vkernel64/x86_64/db_trace.c audit, discovered at rig build time Severity: Low (build regression / platform availability) · Confidence: certain

See VERDICT.md. Stock make nativekernel KERNCONF=VKERNEL64 fails at linking kernel.debug with undefined __build_id_start/__build_id_end: kern.pre.mk:135 adds --build-id=sha1 for all kernels, kern_mib.c references the boundary symbols, pc64 provides them via its ldscript, vkernel64's SYSTEM_LD override (conf/Makefile:23-25) drops ${ELDFLAGS} and its own ldscript is dead (vk_build3.log). fix.diff: defsym both symbols to 0 in SYSTEM_LD (kern_mib then returns ENOENT gracefully). Validated: link + boot.

Build/run:

cd /usr/src && make nativekernel KERNCONF=VKERNEL64     # stock: fails (vk_build2.log)
patch -p1 < fix.diff && make nativekernel KERNCONF=VKERNEL64   # links (vk_fixbuild2.log)

DF-5474 VERDICT — reproduced (build failure), fix validated by link+boot

Bottom line: The stock VKERNEL64 platform cannot build on this tree: sys/conf/kern.pre.mk:135 adds -Wl,--build-id=sha1 to ELDFLAGS for every kernel and sys/kern/kern_mib.c:101-102 references __build_id_start / __build_id_end, which are PROVIDE'd only by the pc64 linker script (sys/platform/pc64/conf/ldscript.x86_64:74-77). The vkernel64 platform overrides SYSTEM_LD (sys/platform/vkernel64/conf/Makefile:23-25) with a plain cc -Wl,--export-dynamic -o kernel.debug ... -pthread link that neither passes ${ELDFLAGS} nor uses the platform ldscript (sys/platform/vkernel64/conf/ldscript.x86_64 is not referenced by any link), so the two externs can never resolve:

vk_build2.log:
/usr/src/sys/kern/kern_mib.c:111: error: undefined reference to '__build_id_end'
/usr/src/sys/kern/kern_mib.c:111: error: undefined reference to '__build_id_start'
/usr/src/sys/kern/kern_mib.c:132: error: undefined reference to '__build_id_start'
collect2: error: ld returned 1 exit status
*** [kernel.debug] Error code 1

vk_build3.log proves the platform ldscript is dead: patching the same .note.gnu.build-id PROVIDE block into it changes nothing (same undefined references), because SYSTEM_LD never passes -T.

Impact: build-regression / platform availability (nobody can have built vkernel64 since the build-id change); kern.build_id is a security-relevant sysctl (build provenance), and vkernel silently has none. Severity Low, confidence certain.

Fix validated

fix.diff: append -Wl,--defsym,__build_id_start=0 -Wl,--defsym,__build_id_end=0 to the vkernel SYSTEM_LD line. kern_mib.c's sysctl then computes sectionlen 0 and returns ENOENT gracefully (kern_mib.c:124-127). Validated on the guest: make nativekernel KERNCONF=VKERNEL64 with the patched conf/Makefile links cleanly (vk_fixbuild2.log: linking kernel.debug → size line, RC=0), the resulting vkernel boots to single-user (vkrun_fixed.log) and behaves correctly under the DF-5472/5473 rig. An alternative upstream-shaped fix is to give vkernel64 a real build-id via its ldscript + -T, but that changes link mode for a userland-executable kernel and was not attempted here.

Reproduce

cd /usr/src && make nativekernel KERNCONF=VKERNEL64   # stock: link error (vk_build2.log)
patch -p1 < fix.diff                                   # defsym in conf/Makefile
make nativekernel KERNCONF=VKERNEL64                   # links + boots

Fix status (batch validation)

Applied with the 36 sibling fix.diffs of this batch in findings/poc/_batch41/all_fixes.patch; single in-guest make -j6 nativekernel KERNCONF=X86_64_GENERIC completed RC=0 with zero errors under -Werror (full log: findings/poc/_batch41/fix_build8.log). Behavior A/B intentionally skipped for this Info-tier item.