* --------------------------- ACCESS VIOLATION SUMMARY ---------------------------
 * LOG FILE: "/var/log/sandbox/sandbox-18316.log"
 * 
VERSION 1.0
FORMAT: F - Function called
FORMAT: S - Access Status
FORMAT: P - Path as passed to function
FORMAT: A - Absolute Path (not canonical)
FORMAT: R - Canonical Path
FORMAT: C - Command Line

F: open_wr
S: deny
P: .git/index.lock
A: /mnt/host/source/src/platform/vboot_reference/.git/index.lock
R: /mnt/host/source/src/platform/vboot_reference/.git/index.lock
C: git describe --dirty --match=v* 

F: open_wr
S: deny
P: .git/index.lock
A: /mnt/host/source/src/platform/vboot_reference/.git/index.lock
R: /mnt/host/source/src/platform/vboot_reference/.git/index.lock
C: git describe --dirty --match=v* 
 * --------------------------------------------------------------------------------

If I comment out lines invoking git in getversion.sh, emerge succeeds. I tried a couple of different boards but this happens only if vboot_reference is cros_worked on.