kpatch-build: account for __pfx_-less NOP padding #1350
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Some kernel configurations generate function NOP padding, but without associated __pfx_<function> symbols. For example: $ git describe HEAD v6.4-rc7-72-gdad9774deaf1 # Initial default config turns on Indirect Branch Tracking and 16-NOP padding bytes $ make defconfig $ grep -e CONFIG_X86_KERNEL_IBT -e CONFIG_FUNCTION_PADDING_BYTES .config CONFIG_X86_KERNEL_IBT=y CONFIG_FUNCTION_PADDING_BYTES=16 # Test .o build generates 16 bytes of NOPs but no "__pfx_" symbol $ make -j$(nproc) fs/proc/cmdline.o $ objdump -Dr -j .text fs/proc/cmdline.o | grep -e '<.*>:' -e 'Disassembly' Disassembly of section .text: 0000000000000000 <cmdline_proc_show-0x10>: 0000000000000010 <cmdline_proc_show>: This is because objtool operation on the object code may be delayed under certain configurations. As such, create-diff-object should be prepared to encounter NOP padded functions in object files before any __pfx_ symbols are created. Fixes: 3e54c63 ("create-diff-object: support x86 NOP-padded functions") Closes: dynup#1347 ("x86 NOP padded functions without __pfx_ symbol") Reported-by: Ryan Sullivan <[email protected]> Signed-off-by: Joe Lawrence <[email protected]>
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Internal testing notes: Ryan reports that this fixes x86-64 integration tests for the v6.3 upstream kernel when CONFIG_X86_KERNEL_IBT=y |
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Unfortunately I'm not sure this approach is safe (see the discussion in #1320). We may have to add support for running create-diff-object on vmlinux.o. |
Ah right thanks for referencing that, I had filed that in my brain as an LTO-specific issue. I'll close this PR, but should we consider throwing an error on |
Yeah, that would probably be a good idea. |
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This PR has been open for 60 days with no activity and no assignee. It will be closed in 7 days unless a comment is added. |
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This PR was closed because it was inactive for 7 days after being marked stale. |
Some kernel configurations generate function NOP padding, but without associated _pfx symbols. For example:
This is because objtool operation on the object code may be delayed under certain configurations. As such, create-diff-object should be prepared to encounter NOP padded functions in object files before any _pfx symbols are created.
Fixes: 3e54c63 ("create-diff-object: support x86 NOP-padded functions")
Closes: #1347 ("x86 NOP padded functions without _pfx symbol")