Re: [PATCH v2 2/2] selftests/ftrace: Convert ELF entry point to file offset in uprobe test
From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Date: 2026-08-07 10:30:18
Also in:
linux-kselftest, lkml
On Fri, 7 Aug 2026 16:15:12 +0800 "Rui Qi" [off-list ref] wrote:
The add_remove_uprobe test uses readelf -h to obtain the ELF entry point (e_entry) and passes it directly as the offset to uprobe_events. However, uprobe_events expects a file offset, not a virtual address. For PIE binaries, the virtual address happens to equal the file offset because the first LOAD segment has p_vaddr == p_offset, so the test works by coincidence. But for non-PIE executables, e_entry is an absolute virtual address that can far exceed the file size. When the probe is enabled, uprobe_register() checks offset > i_size_read(inode) and rejects it with -EINVAL.
Good catch!
Fix this by converting the virtual address to a file offset using the
ELF program headers: scan readelf -lW output for the LOAD segment
containing the entry point, then compute file_offset = e_entry -
p_vaddr + p_offset. For PIE binaries the result is unchanged; for
non-PIE binaries the offset is correctly translated.
The conversion uses only POSIX shell primitives, with no dependency on
gawk or perl.
Fixes: dc4b165855f2 ("selftests/ftrace: Use readelf to find entry point in uprobe test")
Signed-off-by: Rui Qi <redacted>OK, let me take it. Thank you!
quoted hunk ↗ jump to hunk
--- .../test.d/dynevent/add_remove_uprobe.tc | 27 +++++++++++++++++-- 1 file changed, 25 insertions(+), 2 deletions(-)diff --git a/tools/testing/selftests/ftrace/test.d/dynevent/add_remove_uprobe.tc b/tools/testing/selftests/ftrace/test.d/dynevent/add_remove_uprobe.tc index f2048c244526..19430bd5864c 100644 --- a/tools/testing/selftests/ftrace/test.d/dynevent/add_remove_uprobe.tc +++ b/tools/testing/selftests/ftrace/test.d/dynevent/add_remove_uprobe.tc@@ -12,9 +12,32 @@ echo 0 > events/enable echo > dynamic_events REALBIN=`readlink -f /bin/sh` -ENTRYPOINT=`readelf -h ${REALBIN} | grep Entry | sed -e 's/[^0]*//'` -echo "p:myevent ${REALBIN}:${ENTRYPOINT}" >> uprobe_events +# Get the entry point virtual address from ELF header +ENTRY=`readelf -hW ${REALBIN} | grep "Entry point" | awk '{print $NF}'` + +# Convert virtual address to file offset: find the LOAD segment containing +# the entry point, then compute file_offset = e_entry - p_vaddr + p_offset. +# For PIE binaries this is a no-op (vaddr == file offset), but for non-PIE +# executables the virtual address is much larger than the file size and +# must be converted, otherwise uprobe_register() rejects it with -EINVAL. +ENTRY_DEC=$(printf '%d' "$ENTRY") +OFFSET=$ENTRY +while IFS= read -r line; do + set -- $line + [ "$1" = "LOAD" ] || continue + VA_DEC=$(printf '%d' "$3") + OFF_DEC=$(printf '%d' "$2") + FSZ_DEC=$(printf '%d' "$5") + if [ "$ENTRY_DEC" -ge "$VA_DEC" ] && [ "$ENTRY_DEC" -lt "$((VA_DEC + FSZ_DEC))" ]; then + OFFSET=$(printf '0x%x' "$((ENTRY_DEC - VA_DEC + OFF_DEC))") + break + fi +done << EOF +$(readelf -lW ${REALBIN} | grep LOAD) +EOF + +echo "p:myevent ${REALBIN}:${OFFSET}" >> uprobe_events grep -q myevent uprobe_events test -d events/uprobes/myevent-- 2.20.1
-- Masami Hiramatsu (Google) [off-list ref]