kexec: explain kexec_file_load failures - #3774
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On arm, where FileLoad is a stub, kexec printed only "function not implemented", after an "invalid FDT magic" line from the universal payload probe. Neither says what failed or what to do about it. - Name kexec_file_load and the architecture in the ENOSYS stub error. - When kexec_file_load fails with ENOSYS or ENOEXEC, suggest --loadsyscall. ENOEXEC is what riscv returns for an Image before Linux 6.16. - Only log the universal payload probe failure with -d when the file is not an FDT at all, since that is the common case. - Drop "(default true)" from the -d and -L docs; both default to false. On arm the output goes from Failed to load universalpayload (failed to read fdt file: ... invalid FDT magic, got 0x0000a0e1, expected 0xd00dfeed), try legacy kernel.. function not implemented to SYS_kexec_file_load is not supported on arm: function not implemented; try --loadsyscall to use kexec_load instead Fixes u-root#3384 Signed-off-by: Hung-Chun Tseng <alan.tseng.cs@gmail.com>
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Codecov Report❌ Patch coverage is 64.70588% with 6 lines in your changes missing coverage. Please review. @@ Coverage Diff @@
## main #3774 +/- ##
==========================================
- Coverage 61.46% 61.33% -0.14%
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Files 648 648
Lines 45716 45727 +11
==========================================
- Hits 28099 28045 -54
- Misses 17617 17682 +65
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rminnich
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Oct 3, 2026
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cmds/core/kexec/kexec_linux.go
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| return err | ||
| } | ||
| if errors.Is(err, syscall.ENOSYS) || errors.Is(err, syscall.ENOEXEC) { | ||
| return fmt.Errorf("%w; try --loadsyscall to use kexec_load instead", err) |
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I sometimes get complaints from tools that the %w should be last, not first; can you make it last?
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cmds/core/kexec/kexec_linux.go
| } | ||
| } else { | ||
| // universalpayload package suppresses warning message, we print messages here. | ||
| if warningMsg != nil { |
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I am sad to see packages returning nil pointers, it's going to catch us sooner or later. Any chance of fixing that package?
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cmds/core/kexec/kexec_linux.go
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| // case. Only mention it when debugging. | ||
| linux.Debug("%s is not a universal payload (%v), loading it as a kernel", opts.kernelpath, err) | ||
| } else { | ||
| log.Printf("Failed to load universalpayload (%v), try legacy kernel..", err) |
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if this is an error, shouldn't it just return here? This thicket of if ... else might be reduced a bit.
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Awesome, thanks for looking into this! I just referenced this PR in the corresponding issue I had filed a good while ago. |
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Address review on u-root#3774: - A file that is a universal payload but fails to load or execute now returns the error instead of falling back to loading it as a kernel, which could only fail again with a less useful message. The if/else becomes a switch. - Move %w to the end of the --loadsyscall hint. Signed-off-by: Hung-Chun Tseng <alan.tseng.cs@gmail.com>
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Thanks. Pushed 1942ca9:
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Fixes #3384.
On arm, where FileLoad is a stub, kexec printed only function not implemented, after an invalid FDT magic line from the universal payload probe. Neither says what failed or what to do about it.
Before (arm32 vmtest kernel, kexec -l -c KEXEC=Y /kernel):
After:
and on riscv64 with the 6.6 vmtest kernel:
Testing: added TestLoadError; go test ./cmds/core/kexec ./pkg/boot ./pkg/boot/kexec ./pkg/boot/universalpayload passes, and the outputs above are from QEMU runs under runvmtest with VMTEST_ARCH=arm and riscv64.