Alexander Egorenkov <[email protected]> writes:
> Hi,
>
> lijiang <[email protected]> writes:
>
>> On Mon, Mar 28, 2022 at 5:04 PM <[email protected]> wrote:
>>
>>> Date: Mon, 28 Mar 2022 11:03:38 +0200
>>> From: Alexander Egorenkov <[email protected]>
>>> To: "[email protected]" <[email protected]>,
>>> "[email protected]" <[email protected]>
>>> Subject: Re: [Crash-utility] [PATCH] kernel: fix start-up time
>>> degradation caused by strings command
>>> Message-ID: <[email protected]>
>>> Content-Type: text/plain
>>>
>>> "[email protected]" <[email protected]> writes:
>>>
>>> > verify_namelist() uses strings command and scans full part of vmlinux
>>> > file to find linux_banner string. However, vmlinux file is quite large
>>> > these days, reaching over 500MB. As a result, this degradates start-up
>>> > time of crash command 10 or more seconds. (Of course, this depends on
>>> > machines you use for investigation, but I guess typically we cannot
>>> > use such powerful machines to investigate crash dump...)
>>> >
>>> > To resolve this issue, let's use bfd library and read linux_banner
>>> > string in vmlinux file directly.
>>> >
>>> > A simple benchmark shows the following result:
>>> >
>>> > Without the fix:
>>> >
>>> > # cat ./commands.txt
>>> > quit
>>> > # time ./crash -i ./commands.txt \
>>> > /usr/lib/debug/lib/modules/5.16.15-201.fc35.x86_64/vmlinux \
>>> > /var/crash/*/vmcore >/dev/null 2>&1
>>> >
>>> > real 0m20.251s
>>> > user 0m19.022s
>>> > sys 0m1.054s
>>> >
>>> > With the fix:
>>> >
>>> > # time ./crash -i ./commands.txt \
>>> > /usr/lib/debug/lib/modules/5.16.15-201.fc35.x86_64/vmlinux \
>>> > /var/crash/*/vmcore >/dev/null 2>&1
>>> >
>>> > real 0m6.528s
>>> > user 0m6.143s
>>> > sys 0m0.431s
>>> >
>>> > Note that this commit keeps the original logic that uses strings
>>> > command for backward compatibility for in case.
>>> >
>>> > Signed-off-by: HATAYAMA Daisuke <[email protected]>
>>> > ---
>>> > Makefile | 2 +-
>>> > kernel.c | 41 +++++++++++++++++++++++++++++++++++++++++
>>> > 2 files changed, 42 insertions(+), 1 deletion(-)
>>> >
>>> > diff --git a/Makefile b/Makefile
>>> > index 007d030..e520b12 100644
>>> > --- a/Makefile
>>> > +++ b/Makefile
>>> > @@ -364,7 +364,7 @@ task.o: ${GENERIC_HFILES} task.c
>>> > ${CC} -c ${CRASH_CFLAGS} task.c ${WARNING_OPTIONS} ${WARNING_ERROR}
>>> >
>>> > kernel.o: ${GENERIC_HFILES} kernel.c
>>> > - ${CC} -c ${CRASH_CFLAGS} kernel.c ${WARNING_OPTIONS}
>>> ${WARNING_ERROR}
>>> > + ${CC} -c ${CRASH_CFLAGS} kernel.c -I${BFD_DIRECTORY}
>>> -I${GDB_INCLUDE_DIRECTORY} ${WARNING_OPTIONS} ${WARNING_ERROR}
>>> >
>>> > printk.o: ${GENERIC_HFILES} printk.c
>>> > ${CC} -c ${CRASH_CFLAGS} printk.c ${WARNING_OPTIONS}
>>> ${WARNING_ERROR}
>>> > diff --git a/kernel.c b/kernel.c
>>> > index 1c63447..92434a3 100644
>>> > --- a/kernel.c
>>> > +++ b/kernel.c
>>> > @@ -23,6 +23,11 @@
>>> > #include <ctype.h>
>>> > #include <stdbool.h>
>>> > #include "xendump.h"
>>> > +#if defined(GDB_7_6) || defined(GDB_10_2)
>>> > +#define __CONFIG_H__ 1
>>> > +#include "config.h"
>>> > +#endif
>>> > +#include "bfd.h"
>>> >
>>> > static void do_module_cmd(ulong, char *, ulong, char *, char *);
>>> > static void show_module_taint(void);
>>> > @@ -97,6 +102,7 @@ static void dump_printk_safe_seq_buf(int);
>>> > static char *vmcoreinfo_read_string(const char *);
>>> > static void check_vmcoreinfo(void);
>>> > static int is_pvops_xen(void);
>>> > +static int get_linux_banner_from_vmlinux(char *, size_t);
>>> >
>>> >
>>> > /*
>>> > @@ -1324,6 +1330,12 @@ verify_namelist()
>>> > target_smp = strstr(kt->utsname.version, " SMP ") ? TRUE : FALSE;
>>> > namelist_smp = FALSE;
>>> >
>>> > + if (get_linux_banner_from_vmlinux(buffer, sizeof(buffer)) &&
>>> > + strstr(buffer, kt->proc_version)) {
>>> > + found = TRUE;
>>> > + goto found;
>>> > + }
>>> > +
>>> > sprintf(command, "/usr/bin/strings %s", namelist);
>>> > if ((pipe = popen(command, "r")) == NULL) {
>>> > error(INFO, "%s: %s\n", namelist, strerror(errno));
>>> > @@ -1384,6 +1396,7 @@ verify_namelist()
>>> > }
>>> > }
>>> >
>>> > +found:
>>> > if (found) {
>>> > if (CRASHDEBUG(1)) {
>>> > fprintf(fp, "verify_namelist:\n");
>>> > @@ -11770,3 +11783,31 @@ check_vmcoreinfo(void)
>>> > }
>>> > }
>>> > }
>>> > +
>>> > +static
>>> > +int get_linux_banner_from_vmlinux(char *buf, size_t size)
>>> > +{
>>> > + struct bfd_section *sect;
>>> > + long offset;
>>> > +
>>> > + sect = bfd_get_section_by_name(st->bfd, ".rodata");
>>> > + if (!sect)
>>> > + return FALSE;
>>> > +
>>> > + /*
>>> > + * Although symbol_value() returns dynamic symbol value that
>>> > + * is affected by kaslr, which is different from static symbol
>>> > + * value in vmlinux file, but relative offset to linux_banner
>>> > + * object in .rodata section is idential.
>>> > + */
>>> > + offset = symbol_value("linux_banner") - symbol_value(".rodata");
>>> > +
>>> > + if (!bfd_get_section_contents(st->bfd,
>>> > + sect,
>>> > + buf,
>>> > + offset,
>>> > + size))
>>> > + return FALSE;
>>> > +
>>> > + return TRUE;
>>> > +}
>>> > --
>>> > 2.31.1
>>> >
>>> >
>>> >
>>> > --
>>> > Crash-utility mailing list
>>> > [email protected]
>>> > https://listman.redhat.com/mailman/listinfo/crash-utility
>>> > Contribution Guidelines: https://github.com/crash-utility/crash/wiki
>>>
>>> Hi,
>>>
>>> this patch broke crash-utility on s390.
>>> When i try to open a dump file, then i get this error message:
>>>
>>> crash: cannot resolve ".rodata"
>>>
>>>
>> Thank you for pointing out this issue, Alex.
>>
>> Any idea why .rodata symbol is missing ?
>
> Where does the symbol '.rodata' come from ?
> I couldn't find it in x86's vmlinux with nm as well.
>
> On Fedora 34:
>
> $ nm /usr/lib/debug/lib/modules/5.16.16-100.fc34.x86_64/vmlinux | grep rodata
> ffffffff82c1d000 D __end_rodata
> ffffffff82e00000 D __end_rodata_aligned
> ffffffff82e00000 D __end_rodata_hpage_align
> ffffffff81199420 t frob_rodata
> ffffffff81c3eec7 T mark_rodata_ro
> ffffffff826dd200 D rodata_enabled
> ffffffff82e2cec0 d rodata_resource
> ffffffff81352690 T rodata_test
> ffffffff81c50238 t rodata_test.cold
> ffffffff8223d9d0 d rodata_test_data
> ffffffff836c2c36 t set_debug_rodata
> ffffffff838ff890 d __setup_set_debug_rodata
> ffffffff838b4b18 d __setup_str_set_debug_rodata
> ffffffff82200000 D __start_rodata
>
> Regards
> Alex
Found the reason why all symbols starting with '.' are dropped for s390x
/*
* Accept or reject a symbol from the kernel namelist.
*/
static int
s390x_verify_symbol(const char *name, ulong value, char type)
{
int i;
...
/* throw away all symbols containing a '.' */
for(i = 0; i < strlen(name);i++){
if(name[i] == '.') <-------------- !!!
return FALSE;
}
return TRUE;
}
But i have no idea why. Anybody familiar with this ?
Thanks
Regards
Alex
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