[PATCH V2 1/2] tools/perf: Add text_end to "struct dso" to save .text section size

[Athira Rajeev]

> On 18-Aug-2023, at 12:07 PM, Adrian Hunter <adrian.hunter at intel.com> wrote:
> 
> On 17/08/23 20:18, Athira Rajeev wrote:
>> Update "struct dso" to include new member "text_end".
>> This new field will represent the offset for end of text
>> section for a dso. This value is derived as:
>> sh_size (Size of section in byes) + sh_offset (Section file
>> offst) of the elf header for text.
>> 
>> To resolve the address from a sample, perf looks at the
>> DSO maps. In case of address from a kernel module, there
>> were some address found to be not resolved. This was
>> observed while running perf test for "Object code reading".
>> Though the ip falls beteen the start address of the loaded
>> module (perf map->start ) and end address ( perf map->end),
>> it was unresolved.
>> 
>> Example:
>> 
>>    Reading object code for memory address: 0xc008000007f0142c
>>    File is: /lib/modules/6.5.0-rc3+/kernel/fs/xfs/xfs.ko
>>    On file address is: 0x1114cc
>>    Objdump command is: objdump -z -d --start-address=0x11142c --stop-address=0x1114ac /lib/modules/6.5.0-rc3+/kernel/fs/xfs/xfs.ko
>>    objdump read too few bytes: 128
>>    test child finished with -1
>> 
>> Here, module is loaded at:
>>    # cat /proc/modules | grep xfs
>>    xfs 2228224 3 - Live 0xc008000007d00000
>> 
>> From objdump for xfs module, text section is:
>>    text 0010f7bc  0000000000000000 0000000000000000 000000a0 2**4
>> 
>> Here the offset for 0xc008000007f0142c ie  0x112074 falls out
>> .text section which is up to 0x10f7bc.
>> 
>> In this case for module, the address 0xc008000007e11fd4 is pointing
>> to stub instructions. This address range represents the module stubs
>> which is allocated on module load and hence is not part of DSO offset.
>> 
>> To identify such  address, which falls out of text
>> section and within module end, added the new field "text_end" to
>> "struct dso".
>> 
>> Reported-by: Disha Goel <disgoel at linux.ibm.com>
>> Signed-off-by: Athira Rajeev <atrajeev at linux.vnet.ibm.com>
>> ---
>> Changelog:
>>   v1 -> v2:
>>   Changed commit message to explain need for "text_end"
>> 
>> tools/perf/util/dso.h        | 1 +
>> tools/perf/util/symbol-elf.c | 4 +++-
>> 2 files changed, 4 insertions(+), 1 deletion(-)
>> 
>> diff --git a/tools/perf/util/dso.h b/tools/perf/util/dso.h
>> index b41c9782c754..70fe0fe69bef 100644
>> --- a/tools/perf/util/dso.h
>> +++ b/tools/perf/util/dso.h
>> @@ -181,6 +181,7 @@ struct dso {
>> u8  rel;
>> struct build_id  bid;
>> u64  text_offset;
>> + u64  text_end;
>> const char  *short_name;
>> const char  *long_name;
>> u16  long_name_len;
>> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
>> index 8bd466d1c2bd..252d26a59e64 100644
>> --- a/tools/perf/util/symbol-elf.c
>> +++ b/tools/perf/util/symbol-elf.c
>> @@ -1512,8 +1512,10 @@ dso__load_sym_internal(struct dso *dso, struct map *map, struct symsrc *syms_ss,
>> }
>> 
>> if (elf_section_by_name(runtime_ss->elf, &runtime_ss->ehdr, &tshdr,
>> - ".text", NULL))
>> + ".text", NULL)) {
>> dso->text_offset = tshdr.sh_addr - tshdr.sh_offset;
>> + dso->text_end = tshdr.sh_offset + tshdr.sh_size;
>> + }
>> 
>> if (runtime_ss->opdsec)
>> opddata = elf_rawdata(runtime_ss->opdsec, NULL);
> 
> Should probably amend dso__load_bfd_symbols() also

Hi Adrian,

Thanks for checking. Will address this in V2 

Thanks
Athira