Debugging Missing Kernel Headers in LTP Build System

Problem

The LTP build system fails with missing headers (mm.h, module.h) despite kernel headers being installed. Key observations:

  1. GCC commands show no reference to system kernel headers (only LTP internal paths)

  2. Error messages indicate invalid kernel configuration

  3. grep -oP fails due to unsupported Perl regex on the system

Diagnosis

  1. Missing Header Paths:

    • Compiler not searching /usr/src/kernels/$(uname -r)/include

    • No -I flags pointing to system kernel headers

  2. Configuration Issues:

    • LTP’s configure script failed to detect kernel headers

    • Repeated error: ERROR: Kernel configuration is invalid

Debugging Steps

1. Verify Kernel Headers Installation

ls -l /usr/src/kernels/$(uname -r)/include/linux/mm.h
ls -l /lib/modules/$(uname -r)/build/include/linux/module.h

# If missing:
yum install kernel-devel-$(uname -r)

2. Re-run Configure with Debugging

./configure --with-linux-dir=/lib/modules/$(uname -r)/build --verbose 2>&1 | tee configure.log

# Check for:
grep -i "checking for kernel" configure.log

3. Test Header Accessibility

echo "#include <linux/mm.h>" | gcc -E - -I/lib/modules/$(uname -r)/build/include

4. Force Include Paths

export CFLAGS="$CFLAGS -I/lib/modules/$(uname -r)/build/include"
make clean && make

5. Alternative Grep Commands

# For include paths
grep -o -I[^[:space:]]* make_output.log | sort | uniq

# For errors
grep -i "error:" make_output.log

# For missing headers
grep -i "mm.h" make_output.log
grep -i "module.h" make_output.log

Solution Summary

  1. Ensure kernel headers match running kernel version

  2. Explicitly specify kernel path during configure:

    --with-linux-dir=/lib/modules/$(uname -r)/build

  3. Manually add include paths if automatic detection fails

Additional Information

If issues persist, provide:

  • Full configure.log output

  • Results of grep -i "checking for kernel" config.log

  • Complete make V=1 error output