[Crash-utility] [PATCH] kernel: fix start-up time degradation caused by strings command
Alexander Egorenkov
egorenar at linux.ibm.com
Mon Mar 28 11:13:01 UTC 2022
Hi,
lijiang <lijiang at redhat.com> writes:
> On Mon, Mar 28, 2022 at 5:04 PM <crash-utility-request at redhat.com> wrote:
>
>> Date: Mon, 28 Mar 2022 11:03:38 +0200
>> From: Alexander Egorenkov <egorenar at linux.ibm.com>
>> To: "d.hatayama at fujitsu.com" <d.hatayama at fujitsu.com>,
>> "crash-utility at redhat.com" <crash-utility at redhat.com>
>> Subject: Re: [Crash-utility] [PATCH] kernel: fix start-up time
>> degradation caused by strings command
>> Message-ID: <87ee2m4ff9.fsf at oc8242746057.ibm.com>
>> Content-Type: text/plain
>>
>> "d.hatayama at fujitsu.com" <d.hatayama at fujitsu.com> 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 <d.hatayama at fujitsu.com>
>> > ---
>> > 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
>> > Crash-utility at redhat.com
>> > 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
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