Linux Debug Tricks
This page contains many helpful suggestions for debugging issue with the Linux kernel.
Common Tools
- grep : The kernel has thousands of files. The grep tool is the most powerful way to find what you are looking for. Use the -R to search recursively . Remember that grep is case sensitive by default, so use -i if you need it to ignore case.
- And example to find a function name start_kernel: $ grep -r "start_kernel"
- find : Sometimes someone will give you just a filename, and the find command can help you find where that file is. Also, it find is very helpful when combined with grep.
- For example, if you just want to search header files: $ find * -name "*.h" | grep purple
Error Messages
- Many times an error message will be printed out. This happens a lot for a device driver that has trouble initializing during boot.
- Your first step should be to find what source code file is print that message
- Simply use the grep command with -R option and search for that error message.
Error Codes
- If a error message prints out an error code, for example "-110", you should look up what the error code means.
- You can find a list of the error code numbers mean in file include/uapi/asm-generic/errno-base.h
- Since the code will use the #defrine name (not the actual number), you can then search driver file for when that error code/name is returned.
Finding the Device Driver File
- When adding or configuring a driver to your system, you will probably be editing the Device Tree.
- If there is an issue with that driver or peripheral, you will need to find the source code for the driver
- You can use the "compatible" name listed in the device tree, and grep, in order to find the location of the device driver file.
- Do you search starting in the "drivers" directory (to avoid all the matches that will be found in other device tree files)
- Example: Find the Watchdog Timer Driver
- RZ/G2L Device Tree: rz_linux-cip/arch/arm64/boot/dts/renesas/r9a07g044.dtsi
wdt0: watchdog@12800800 { compatible = "renesas,r9a07g044-wdt", "renesas,rzg2l-wdt"; reg = <0 0x12800800 0 0x400>; clocks = <&cpg CPG_MOD R9A07G044_WDT0_PCLK>, <&cpg CPG_MOD R9A07G044_WDT0_CLK>; clock-names = "pclk", "oscclk"; interrupts = <GIC_SPI 49 IRQ_TYPE_LEVEL_HIGH>, <GIC_SPI 50 IRQ_TYPE_LEVEL_HIGH>; interrupt-names = "wdt", "perrout"; resets = <&cpg R9A07G044_WDT0_PRESETN>; power-domains = <&cpg>; status = "disabled"; };
- Use the grep command:
$ grep -R "renesas,rzg2l-wdt" * arch/arm64/boot/dts/renesas/r9a07g044.dtsi: "renesas,rzg2l-wdt"; arch/arm64/boot/dts/renesas/r9a07g044.dtsi: "renesas,rzg2l-wdt"; arch/arm64/boot/dts/renesas/r9a07g044.dtsi: "renesas,rzg2l-wdt"; arch/arm64/boot/dts/renesas/r9a07g043.dtsi: "renesas,rzg2l-wdt"; arch/arm64/boot/dts/renesas/r9a07g043.dtsi: "renesas,rzg2l-wdt"; arch/arm64/boot/dts/renesas/r9a07g054.dtsi: "renesas,rzg2l-wdt"; arch/arm64/boot/dts/renesas/r9a07g054.dtsi: "renesas,rzg2l-wdt"; arch/arm64/boot/dts/renesas/r9a07g054.dtsi: "renesas,rzg2l-wdt"; Documentation/devicetree/bindings/watchdog/renesas,wdt.yaml: - const: renesas,rzg2l-wdt # RZ/G2L Documentation/devicetree/bindings/watchdog/renesas,wdt.yaml: - renesas,rzg2l-wdt drivers/watchdog/rzg2l_wdt.c: { .compatible = "renesas,rzg2l-wdt", }, scripts/dtc/include-prefixes/arm64/renesas/r9a07g044.dtsi: "renesas,rzg2l-wdt"; scripts/dtc/include-prefixes/arm64/renesas/r9a07g044.dtsi: "renesas,rzg2l-wdt"; scripts/dtc/include-prefixes/arm64/renesas/r9a07g044.dtsi: "renesas,rzg2l-wdt"; scripts/dtc/include-prefixes/arm64/renesas/r9a07g043.dtsi: "renesas,rzg2l-wdt"; scripts/dtc/include-prefixes/arm64/renesas/r9a07g043.dtsi: "renesas,rzg2l-wdt"; scripts/dtc/include-prefixes/arm64/renesas/r9a07g054.dtsi: "renesas,rzg2l-wdt"; scripts/dtc/include-prefixes/arm64/renesas/r9a07g054.dtsi: "renesas,rzg2l-wdt"; scripts/dtc/include-prefixes/arm64/renesas/r9a07g054.dtsi: "renesas,rzg2l-wdt";
- RZ/G2L Device Tree: rz_linux-cip/arch/arm64/boot/dts/renesas/r9a07g044.dtsi
- Example: Find the UART Driver
- RZ/G2L Device Tree: rz_linux-cip/arch/arm64/boot/dts/renesas/r9a07g044.dtsi
scif0: serial@1004b800 { compatible = "renesas,scif-r9a07g044"; reg = <0 0x1004b800 0 0x400>; interrupts = <GIC_SPI 380 IRQ_TYPE_LEVEL_HIGH>, <GIC_SPI 382 IRQ_TYPE_LEVEL_HIGH>, <GIC_SPI 383 IRQ_TYPE_LEVEL_HIGH>, <GIC_SPI 381 IRQ_TYPE_LEVEL_HIGH>, <GIC_SPI 384 IRQ_TYPE_LEVEL_HIGH>, <GIC_SPI 384 IRQ_TYPE_LEVEL_HIGH>; interrupt-names = "eri", "rxi", "txi", "bri", "dri", "tei"; clocks = <&cpg CPG_MOD R9A07G044_SCIF0_CLK_PCK>; clock-names = "fck"; power-domains = <&cpg>; resets = <&cpg R9A07G044_SCIF0_RST_SYSTEM_N>; status = "disabled"; };
- Use the grep command:
$ cd drivers $ grep -R "renesas,scif-r9a07g044" *
- RZ/G2L Device Tree: rz_linux-cip/arch/arm64/boot/dts/renesas/r9a07g044.dtsi