[PATCH] scripts/gdb: fix debugging modules compiled with hot/cold partitioning

[PATCH] scripts/gdb: fix debugging modules compiled with hot/cold partitioning

[Ilya Leoshkevich]

gcc's -freorder-blocks-and-partition option makes it group frequently
and infrequently used code in .text.hot and .text.unlikely sections
respectively. At least when building modules on s390, this option is
used by default.

gdb assumes that all code is located in .text section, and that .text
section is located at module load address. With such modules this is no
longer the case: there is code in .text.hot and .text.unlikely, and
either of them might precede .text.

Fix by explicitly telling gdb the addresses of code sections.

It might be tempting to do this for all sections, not only the ones in
the white list. Unfortunately, gdb appears to have an issue, when telling
it about e.g. loadable .note.gnu.build-id section causes it to think that
non-loadable .note.Linux section is loaded at address 0, which in turn
causes NULL pointers to be resolved to bogus symbols. So keep using the
white list approach for the time being.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 scripts/gdb/linux/symbols.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/scripts/gdb/linux/symbols.py b/scripts/gdb/linux/symbols.py
index 7b7c2fafbc68..be984aa29b75 100644
--- a/scripts/gdb/linux/symbols.py
+++ b/scripts/gdb/linux/symbols.py
@@ -99,7 +99,8 @@ lx-symbols command."""
             attrs[n]['name'].string(): attrs[n]['address']
             for n in range(int(sect_attrs['nsections']))}
         args = []
-        for section_name in [".data", ".data..read_mostly", ".rodata", ".bss"]:
+        for section_name in [".data", ".data..read_mostly", ".rodata", ".bss",
+                             ".text", ".text.hot", ".text.unlikely"]:
             address = section_name_to_address.get(section_name)
             if address:
                 args.append(" -s {name} {addr}".format(
-- 
2.23.0

Re: [PATCH] scripts/gdb: fix debugging modules compiled with hot/cold partitioning

[Jan Kiszka]

On 28.10.19 16:27, Ilya Leoshkevich wrote:
> gcc's -freorder-blocks-and-partition option makes it group frequently
> and infrequently used code in .text.hot and .text.unlikely sections
> respectively. At least when building modules on s390, this option is
> used by default.
> 
> gdb assumes that all code is located in .text section, and that .text
> section is located at module load address. With such modules this is no
> longer the case: there is code in .text.hot and .text.unlikely, and
> either of them might precede .text.
> 
> Fix by explicitly telling gdb the addresses of code sections.
> 
> It might be tempting to do this for all sections, not only the ones in
> the white list. Unfortunately, gdb appears to have an issue, when telling
> it about e.g. loadable .note.gnu.build-id section causes it to think that
> non-loadable .note.Linux section is loaded at address 0, which in turn
> causes NULL pointers to be resolved to bogus symbols. So keep using the
> white list approach for the time being.

Did you report this to gdb?

> 
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
>  scripts/gdb/linux/symbols.py | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/scripts/gdb/linux/symbols.py b/scripts/gdb/linux/symbols.py
> index 7b7c2fafbc68..be984aa29b75 100644
> --- a/scripts/gdb/linux/symbols.py
> +++ b/scripts/gdb/linux/symbols.py
> @@ -99,7 +99,8 @@ lx-symbols command."""
>              attrs[n]['name'].string(): attrs[n]['address']
>              for n in range(int(sect_attrs['nsections']))}
>          args = []
> -        for section_name in [".data", ".data..read_mostly", ".rodata", ".bss"]:
> +        for section_name in [".data", ".data..read_mostly", ".rodata", ".bss",
> +                             ".text", ".text.hot", ".text.unlikely"]:
>              address = section_name_to_address.get(section_name)
>              if address:
>                  args.append(" -s {name} {addr}".format(
> 

Reviewed-by: Jan Kiszka <jan.kiszka@siemens.com>

Jan

-- 
Siemens AG, Corporate Technology, CT RDA IOT SES-DE
Corporate Competence Center Embedded Linux

Re: [PATCH] scripts/gdb: fix debugging modules compiled with hot/cold partitioning

[Ilya Leoshkevich]

> Am 30.10.2019 um 19:29 schrieb Jan Kiszka <jan.kiszka@siemens.com>:
> 
> On 28.10.19 16:27, Ilya Leoshkevich wrote:
>> gcc's -freorder-blocks-and-partition option makes it group frequently
>> and infrequently used code in .text.hot and .text.unlikely sections
>> respectively. At least when building modules on s390, this option is
>> used by default.
>> 
>> gdb assumes that all code is located in .text section, and that .text
>> section is located at module load address. With such modules this is no
>> longer the case: there is code in .text.hot and .text.unlikely, and
>> either of them might precede .text.
>> 
>> Fix by explicitly telling gdb the addresses of code sections.
>> 
>> It might be tempting to do this for all sections, not only the ones in
>> the white list. Unfortunately, gdb appears to have an issue, when telling
>> it about e.g. loadable .note.gnu.build-id section causes it to think that
>> non-loadable .note.Linux section is loaded at address 0, which in turn
>> causes NULL pointers to be resolved to bogus symbols. So keep using the
>> white list approach for the time being.
> 
> Did you report this to gdb?

Yes: https://sourceware.org/bugzilla/show_bug.cgi?id=25152

Best regards,
Ilya