[PATCH 2/2] selftests/ftrace: Convert ELF entry point to file offset in uprobe test
From: Rui Qi <hidden>
Date: 2026-08-06 08:31:40
Also in:
linux-kselftest, lkml
Subsystem:
kernel selftest framework, the rest, tracing · Maintainers:
Shuah Khan, Shuah Khan, Linus Torvalds, Steven Rostedt, Masami Hiramatsu
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 (ET_DYN), 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 (ET_EXEC),
e_entry is an absolute virtual address (e.g. 0x406ad0) that far exceeds
the file size (e.g. 0x7be60). When the probe is enabled, uprobe_register()
checks offset > i_size_read(inode) and rejects it with -EINVAL.
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 (printf, arithmetic
expansion) 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>
---
.../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 f33a863be68b..9207fd817aae 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=`LC_ALL=C 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=`LC_ALL=C 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' "$((ENTRY_DEC - VA_DEC + OFF_DEC))") + break + fi +done << EOF +$(LC_ALL=C 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