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SubjectRe: [RFC][PATCH v4 27/32] objtool: mcount: Generic location and relocation table types
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On 6/9/20 11:42 PM, Matt Helsley wrote:

[...]

>> Hi Matt,
>>
>> I was trying out the patch series on ppc64le and found that __mcount_loc
>> and .rela__mcount_loc section pairs do not get generated.
>>
>> # readelf -S fs/proc/cmdline.o|grep mcount
>> #
>>
>> Debugged the cause to get_mcountsym()'s return type. It returns reloc
>> type from GELF_R_INFO() and expects Elf64_Xword a.k.a unsigned long
>> to be the return type but get_mcountsym() returns unsigned int on 64-bit.
>>
>> On power the _mcount is of relocation type R_PPC64_REL24 (info 0x170000000a),
>> using unsigned int truncates the value to 0xa and fails the above check.
>> Using below fix, that converts mcount_sym_info to use unsigned long, generates
>> the __mcount_loc section pairs.
>>
>> --- a/tools/objtool/mcount.c
>> +++ b/tools/objtool/mcount.c
>> @@ -163,7 +163,7 @@ static int is_mcounted_section_name(char const *const txtname)
>> strcmp(".cpuidle.text", txtname) == 0;
>> }
>>
>> -static unsigned int get_mcount_sym_info(struct reloc *reloc)
>> +static unsigned long get_mcount_sym_info(struct reloc *reloc)
>> {
>> struct symbol *sym = reloc->sym;
>> char const *symname = sym->name;
>> @@ -274,7 +274,7 @@ static int nop_mcount(struct section * const rels,
>> {
>> struct reloc *reloc;
>> struct section *txts = find_section_by_index(lf, rels->sh.sh_info);
>> - unsigned int mcount_sym_info = 0;
>> + unsigned long mcount_sym_info = 0;
>> int once = 0;
>>
>> list_for_each_entry(reloc, &rels->reloc_list, list) {
>> @@ -363,7 +363,7 @@ static void sift_rel_mcount(GElf_Addr **mlocpp,
>> {
>> GElf_Rel *mrelp = *mrelpp;
>> GElf_Rela *mrelap = *mrelpp;
>> - unsigned int mcount_sym_info = 0;
>> + unsigned long mcount_sym_info = 0;
>> struct reloc *reloc;
>>
>> list_for_each_entry(reloc, &rels->reloc_list, list) {
>>
>> # readelf -S fs/proc/cmdline.o|grep mcount
>> [31] __mcount_loc PROGBITS 0000000000000000 00022f10
>> [32] .rela__mcount_loc RELA 0000000000000000 00022f20
>
> Fixed for next posting.
>
> I've essentially added this as another patch before it moves into
> recordmcount.c, gets renamed to get_mcount_sym_info(), etc. I did it
> this way because it only becomes necessary to change the type before
> moving the function (and eventually its callers) out of the wrapper.
>
> I feel I should credit you as author or at least co-author of the added
> patch since it's basically a "backported" version of the changes you
> suggested. I reviewed the process in submitting-patches.rst and propose
> the commit message:
>
> objtool: mcount: Extend mcountsym size
>
> Before we can move this function out of the wrapper and into
> wordsize-independent code we need to explicitly size the
> type returned from get_mcountsym() to preserve the symbol info.
>
> Reported-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
> Signed-off-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
> Signed-off-by: Matt Helsley <mhelsley@vmware.com>
>
> Is that OK with you or do you have another preference?

Thanks, it works for me.

--
Kamalesh

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