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selftests/ftrace: Convert ELF entry point to file offset in uprobe test

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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.

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.

Link: https://lore.kernel.org/all/20260807081512.2974757-3-qirui.001@bytedance.com/

Fixes: dc4b165855 ("selftests/ftrace: Use readelf to find entry point in uprobe test")
Cc: stable@vger.kernel.org
Signed-off-by: Rui Qi <qirui.001@bytedance.com>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
This commit is contained in:
Rui Qi 2026-08-07 16:15:12 +08:00 committed by Masami Hiramatsu (Google)
parent f9a2394a23
commit 24aa630f62
1 changed files with 25 additions and 2 deletions
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27
tools/testing/selftests/ftrace/test.d/dynevent/add_remove_uprobe.tc
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@ -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