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Kernel Build — FAQ

This page covers common errors and troubleshooting tips encountered during the build process. When something goes wrong, always read the full build log first — the real cause of a failure almost always appears above the Error 2 line.

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Before the Build

Q1: Why do I get No such file or directory?

Cause: The compiler cannot find a required header file (.h) or source file (.c) at the specified path.

Fix:

• Double-check that all file paths are correct
• If a system header is missing, install the corresponding dependency library, for example:

sudo apt install libssl-dev zlib1g-dev

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Q2: I see cannot open involving a .gz file?

Cause: The required kernel configuration file was never generated, or was wiped by a previous make mrproper.

Fix: Re-run the defconfig command to regenerate it:

make ARCH=arm64 O=out <your_defconfig>

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Build Errors (Error 2)

Compiler & Toolchain Compatibility

Q3: I see unrecognized command line option?

Cause: The current toolchain version does not match what the kernel source expects — either too old or too new — so a compiler flag is not recognized.

Fix: Check the relevant compiler flags in the Makefile and consider upgrading or downgrading your GCC / Clang version accordingly.

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Q4: I see target emulation unknown?

Cause: The linker (ld) does not recognize the specified emulation mode. This is typically caused by mixing LLVM and GNU toolchain components.

Fix: Make sure the LD variable points to the correct linker for your toolchain. When using LLVM, set:

LD=ld.lld

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Q5: I see assembler command failed with exit code 1?

Cause: The assembler reported an error, usually an internal Clang issue or a version incompatibility.

Fix: Try switching to a different version of Clang.

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KernelSU-Specific

Q6: I see MODULE_IMPORT_NS(...) VFS_internal...?

Cause: The official KernelSU is incompatible with Non-GKI kernels, or the wrong fork branch is being used.

Fix:

• Official KernelSU: Try rolling back to an older release such as v0.9.5
• Fork: Switch to the correct branch. For example, with SukiSU-Ultra, Non-GKI kernels require the builtin branch, not main

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Clang Issues

Q7: I see not found (required by clang)?

Cause: The host system is too old to run the version of Clang you are using.

Fix: Upgrade your OS. Ubuntu 22.04 or later is recommended.

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Q8: I see Error: junk at end of line...?

Cause: The assembler cannot parse the debug information produced by a newer Clang — a DWARF format version mismatch.

Fix (choose one):

• Downgrade Clang to a lower version (e.g. from Clang 20 to Clang 12)
• Add the following flag to KBUILD_CFLAGS in your Makefile to force a compatible DWARF format:

KBUILD_CFLAGS += -gdwarf-4

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Code & Syntax Errors

Q9: I see undefined reference to ...?

Cause: A linker error — a function is declared but its implementation cannot be found (missing library or object file).

Fix:

• Check whether a required library is missing from the link step (e.g. -lssl)
• Confirm the library path is included in LDFLAGS
• Check for typos in function names

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Q10: I see a misleading-indentation warning or error?

Cause: Code indentation does not match the logical control block structure (if / for / while), creating a potential logic trap.

Fix: Add explicit curly braces {} to the affected statements to make the scope unambiguous.

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Q11: I see type specifier missing or makes pointer from integer...?

Cause: A C variable declaration is missing a type keyword, or there is a type mismatch (e.g. an integer being used where a pointer is expected).

Fix:

• Check whether type keywords like int are missing from variable declarations
• Verify whether the kernel API being used has changed between versions

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Other Build Issues

Q12: I see multiple definition of 'yylloc'?

Cause: This is a well-known conflict between older kernel source code and newer versions of GCC.

Fix: Edit scripts/dtc/dtc-lexer.lex.c_shipped and change:

YYLTYPE yylloc;

to:

extern YYLTYPE yylloc;

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Q13: I see make[N]: *** [Error X] — what does that mean?

Cause: This is a generic Makefile build failure marker. It contains no useful diagnostic information on its own.

Fix: This line is just the result — the actual error is above it. Scroll up in the log and look for the specific error message emitted by gcc, ld, or sh.

Q14：I see undefined symbol: __stack_chk_guard？

Cause：This is the classic STACKPROTECTOR error call problem generated by higher versions of Clang.

Fix：Downgrading the Clang version. Usually downgrading to 12 or 10 allows Clang to drop the newer STACKPROTECTOR and compile in a more traditional way.