[PATCH] perf machine: Don't ignore _etext when not a text symbol

[PATCH] perf machine: Don't ignore _etext when not a text symbol

[Christophe Leroy]

Depending on how vmlinux.lds is written, _etext might be the very
first data symbol instead of the very last text symbol.

Don't require it to be a text symbol, accept any symbol type.

Fixes: ed9adb2035b5 ("perf machine: Read also the end of the kernel")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 tools/perf/util/machine.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 27d5345d2b30..9be2f4479f52 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -1003,7 +1003,7 @@ static int machine__get_running_kernel_start(struct machine *machine,
 
 	err = kallsyms__get_symbol_start(filename, "_edata", &addr);
 	if (err)
-		err = kallsyms__get_function_start(filename, "_etext", &addr);
+		err = kallsyms__get_symbol_start(filename, "_etext", &addr);
 	if (!err)
 		*end = addr;
 
-- 
2.47.0

Re: [PATCH] perf machine: Don't ignore _etext when not a text symbol

[Arnaldo Carvalho de Melo]

On Wed, Jan 08, 2025 at 10:15:24AM +0100, Christophe Leroy wrote:
> Depending on how vmlinux.lds is written, _etext might be the very
> first data symbol instead of the very last text symbol.
> 
> Don't require it to be a text symbol, accept any symbol type.

I'm adding a Link:

Link: https://lore.kernel.org/all/752a31b0-4370-4f52-b7cc-45f0078c1d6c@csgroup.eu

To give more context as where this has been observed, and also add a
snippet of your explanation there, this:

----
# grep -e _stext -e _etext -e _edata /proc/kallsyms
c0000000 T _stext
c08b8000 D _etext

So there is no _edata and _etext is not text

$ ppc-linux-objdump -x vmlinux | grep -e _stext -e _etext -e _edata
c0000000 g       .head.text	00000000 _stext
c08b8000 g       .rodata	00000000 _etext
c1378000 g       .sbss	00000000 _edata
----

Thanks,

- Arnaldo

> Fixes: ed9adb2035b5 ("perf machine: Read also the end of the kernel")
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
>  tools/perf/util/machine.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> index 27d5345d2b30..9be2f4479f52 100644
> --- a/tools/perf/util/machine.c
> +++ b/tools/perf/util/machine.c
> @@ -1003,7 +1003,7 @@ static int machine__get_running_kernel_start(struct machine *machine,
>  
>  	err = kallsyms__get_symbol_start(filename, "_edata", &addr);
>  	if (err)
> -		err = kallsyms__get_function_start(filename, "_etext", &addr);
> +		err = kallsyms__get_symbol_start(filename, "_etext", &addr);
>  	if (!err)
>  		*end = addr;
>  
> -- 
> 2.47.0

Re: [PATCH] perf machine: Don't ignore _etext when not a text symbol

[Christophe Leroy]

Le 08/01/2025 à 21:14, Arnaldo Carvalho de Melo a écrit :
> On Wed, Jan 08, 2025 at 10:15:24AM +0100, Christophe Leroy wrote:
>> Depending on how vmlinux.lds is written, _etext might be the very
>> first data symbol instead of the very last text symbol.
>>
>> Don't require it to be a text symbol, accept any symbol type.
> 
> I'm adding a Link:
> 
> Link: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fall%2F752a31b0-4370-4f52-b7cc-45f0078c1d6c%40csgroup.eu&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C914f4c7995574ee91f5c08dd30211dd6%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638719640997470461%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=kqCNbhhgKri3TlJaUb3mkTU6NyFRzhnb%2BDiK93h9aSQ%3D&reserved=0
> 
> To give more context as where this has been observed, and also add a
> snippet of your explanation there, this:
> 
> ----
> # grep -e _stext -e _etext -e _edata /proc/kallsyms
> c0000000 T _stext
> c08b8000 D _etext
> 
> So there is no _edata and _etext is not text

For the absence of _edata, I sent another patch, will you take it as 
well ? :

https://lore.kernel.org/linux-perf-users/2fec8c50c271dff59f0177ff0884b6c374486ba5.1736327770.git.christophe.leroy@csgroup.eu/T/#u

Thanks
Christophe