Comments (6)
See comparison of cmdline_proc_show() for when CONFIG_FTRACE_MCOUNT_USE_OBJTOOL vs CONFIG_FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY:
--- mcount_objtool 2024-03-25 15:31:39.819471809 -0400
+++ mcount_patchable_fun_entry 2024-03-25 15:32:10.441579666 -0400
@@ -5,7 +5,6 @@ Disassembly of section .text.cmdline_pro
0: R_PPC64_REL16_HA .TOC.
4: 00 00 42 38 addi r2,r2,0
4: R_PPC64_REL16_LO .TOC.+0x4
- 8: a6 02 08 7c mflr r0
- c: 01 00 00 48 bl c <cmdline_proc_show+0xc>
- c: R_PPC64_REL24 _mcount
+ 8: 00 00 00 60 nop
+ c: 00 00 00 60 nop
10: a6 02 08 7c mflr r0
The checks in kpatch_find_func_profiling_calls() for the PPC64 arch look for that "_mcount" relocation, which isn't present in the patchable-function-entry case.
To support this config, we could look for the nop instructions directly, like the S390 case, or maybe verify that there is a "patchable_function_entries" relocation for the function. This gets a little weird as the compiler seems to generate multiple __patchable_function_entries sections (one for each section?):
$ objdump -j__patchable_function_entries -r fs/proc/cmdline.o
fs/proc/cmdline.o: file format elf64-powerpcle
RELOCATION RECORDS FOR [__patchable_function_entries]:
OFFSET TYPE VALUE
0000000000000000 R_PPC64_ADDR64 .init.text+0x0000000000000008
RELOCATION RECORDS FOR [__patchable_function_entries]:
OFFSET TYPE VALUE
0000000000000000 R_PPC64_ADDR64 .text.cmdline_proc_show+0x0000000000000008
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Multiple sections with the same name, weird :-) IMO, checking for the nops is probably sufficient.
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This issue has been open for 30 days with no activity and no assignee. It will be closed in 7 days unless a comment is added.
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This issue has been open for 30 days with no activity and no assignee. It will be closed in 7 days unless a comment is added.
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This issue was closed because it was inactive for 7 days after being marked stale.
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