Re: [PATCH V5 1/3] tools/perf: Add text_end to "struct dso" to save .text section size

[Namhyung Kim <namhyung@kernel.org>]

Hello,

On Thu, Sep 28, 2023 at 12:52 AM Athira Rajeev
<atrajeev@linux.vnet.ibm.com> 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. For elf, this value is derived as:
> sh_size (Size of section in byes) + sh_offset (Section file
> offst) of the elf header for text.
>
> For bfd, this value is derived as:
> 1. For PE file,
> section->size + ( section->vma - dso->text_offset)
> 2. Other cases:
> section->filepos (file position) + section->size (size of
> section)
>
> 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@linux.ibm.com>
> Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
> Reviewed-by: Adrian Hunter <adrian.hunter@intel.com>
> Reviewed-by: Kajol Jain <kjain@linux.ibm.com>

For the series,
Acked-by: Namhyung Kim <namhyung@kernel.org>

Thanks,
Namhyung


> ---
> Changelog:
> v2 -> v3:
>  Added Reviewed-by from Adrian
>
>  v1 -> v2:
>  Added text_end for bfd also by updating dso__load_bfd_symbols
>  as suggested by Adrian.
>
>  tools/perf/util/dso.h        | 1 +
>  tools/perf/util/symbol-elf.c | 4 +++-
>  tools/perf/util/symbol.c     | 2 ++
>  3 files changed, 6 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 95e99c332d7e..9e7eeaf616b8 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -1514,8 +1514,10 @@ 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);
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index 3f36675b7c8f..f25e4e62cf25 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -1733,8 +1733,10 @@ int dso__load_bfd_symbols(struct dso *dso, const char *debugfile)
>                         /* PE symbols can only have 4 bytes, so use .text high bits */
>                         dso->text_offset = section->vma - (u32)section->vma;
>                         dso->text_offset += (u32)bfd_asymbol_value(symbols[i]);
> +                       dso->text_end = (section->vma - dso->text_offset) + section->size;
>                 } else {
>                         dso->text_offset = section->vma - section->filepos;
> +                       dso->text_end = section->filepos + section->size;
>                 }
>         }
>
> --
> 2.31.1
>