[Crash-utility] Re: [PATCH] Revert "vmcoreinfo: read vmcoreinfo using 'vmcoreinfo_data' when unavailable in elf note"

On Wed, Nov 19, 2025 at 12:51 PM <devel-request(a)lists.crash-utility.osci.io&gt; wrote: > > Date: Wed, 19 Nov 2025 17:06:32 +1300 > From: Tao Liu <ltao(a)redhat.com&gt; > Subject: [Crash-utility] [PATCH] Revert "vmcoreinfo: read vmcoreinfo > using 'vmcoreinfo_data' when unavailable in elf note" > To: devel(a)lists.crash-utility.osci.io > Cc: Tao Liu <ltao(a)redhat.com&gt; > Message-ID: <20251119040631.19214-2-ltao(a)redhat.com&gt; > Content-Type: text/plain; charset="US-ASCII"; x-default=true > > This patch will cause a regression on some x86_64 vmcores. > > $ crash -s vmcore vmlinux.gz > WARNING: vmcoreinfo is empty, will read from symbols > crash: cannot malloc vmcoreinfo buffer > crash: /var/tmp/vmlinux.gz_fWV3kA and vmcore do not match! > > The root cause is, in main.c, is_kdump() calls is_netdump(), which will > set pc->read_vmcoreinfo as vmcoreinfo_read_from_memory(), rather than > original vmcoreinfo_read_string(). > > Later in machdep_init(PRE_SYMTAB), vmcoreinfo_read_from_memory() doesn't > get "relocate" string, so fails for set kaslr flag, then fails for > linux_banner detection: > > Thread 1 "crash" hit Breakpoint 2, verify_version (): > 1096 if (!IS_KVADDR(linux_banner)) > (gdb) p/x linux_banner > $4 = 0xffffffff81e00100 > > crash> sym linux_banner > ffffffff9aa00100 (R) linux_banner > > As we can see with the patch applied, linux_banner got a wrong address. > So this patch currently is unsafe, and should be reverted before the fix. > > Signed-off-by: Tao Liu <ltao(a)redhat.com&gt; > --- > > Since it is too close to the new release date of crash utility, I don't > have enough time for full root cause analysis and re-testing. So currently > the best option is to revert it for now, and fix it in the next release then > re-apply. > Agree. Thanks for working on it, Tao. So: Acke Lianbo > --- > defs.h | 1 - > diskdump.c | 18 ------------------ > kernel.c | 17 +++++------------ > netdump.c | 19 ------------------- > 4 files changed, 5 insertions(+), 50 deletions(-) > > diff --git a/defs.h b/defs.h > index ab4aee8..ae6ea01 100644 > --- a/defs.h > +++ b/defs.h > @@ -6225,7 +6225,6 @@ void dump_kernel_table(int); > void dump_bt_info(struct bt_info *, char *where); > void dump_log(int); > void parse_kernel_version(char *); > -char *vmcoreinfo_read_from_memory(const char *); > > #define LOG_LEVEL(v) ((v) & 0x07) > #define SHOW_LOG_LEVEL (0x1) > diff --git a/diskdump.c b/diskdump.c > index de90755..ce3cbb7 100644 > --- a/diskdump.c > +++ b/diskdump.c > @@ -1041,13 +1041,6 @@ pfn_to_pos(ulong pfn) > return desc_pos; > } > > -/** > - * Check if vmcoreinfo in vmcore is missing/empty > - */ > -static bool is_diskdump_vmcoreinfo_empty(void) > -{ > - return (dd->sub_header_kdump->size_vmcoreinfo == 0); > -} > > /* > * Determine whether a file is a diskdump creation, and if TRUE, > @@ -1095,17 +1088,6 @@ is_diskdump(char *file) > > pc->read_vmcoreinfo = vmcoreinfo_read_string; > > - /* > - * vmcoreinfo can be empty in case of dump collected via virsh-dump > - * > - * check if vmcoreinfo is not available in vmcore, and try to read > - * the vmcoreinfo from memory, using "vmcoreinfo_data" symbol > - */ > - if (is_diskdump_vmcoreinfo_empty()) { > - error(WARNING, "vmcoreinfo is empty, will read from symbols\n"); > - pc->read_vmcoreinfo = vmcoreinfo_read_from_memory; > - } > - > if ((pc->flags2 & GET_LOG) && KDUMP_CMPRS_VALID()) { > pc->dfd = dd->dfd; > pc->readmem = read_diskdump; > diff --git a/kernel.c b/kernel.c > index 13f3374..e077275 100644 > --- a/kernel.c > +++ b/kernel.c > @@ -99,6 +99,7 @@ static ulong dump_audit_skb_queue(ulong); > static ulong __dump_audit(char *); > static void dump_audit(void); > 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); > @@ -11894,8 +11895,8 @@ dump_printk_safe_seq_buf(int msg_flags) > * Returns a string (that has to be freed by the caller) that contains the > * value for key or NULL if the key has not been found. > */ > -char * > -vmcoreinfo_read_from_memory(const char *key) > +static char * > +vmcoreinfo_read_string(const char *key) > { > char *buf, *value_string, *p1, *p2; > size_t value_length; > @@ -11905,14 +11906,6 @@ vmcoreinfo_read_from_memory(const char *key) > > buf = value_string = NULL; > > - if (!(pc->flags & GDB_INIT)) { > - /* > - * GDB interface hasn't been initialised yet, so can't > - * access vmcoreinfo_data > - */ > - return NULL; > - } > - > switch (get_symbol_type("vmcoreinfo_data", NULL, NULL)) > { > case TYPE_CODE_PTR: > @@ -11968,10 +11961,10 @@ check_vmcoreinfo(void) > switch (get_symbol_type("vmcoreinfo_data", NULL, NULL)) > { > case TYPE_CODE_PTR: > - pc->read_vmcoreinfo = vmcoreinfo_read_from_memory; > + pc->read_vmcoreinfo = vmcoreinfo_read_string; > break; > case TYPE_CODE_ARRAY: > - pc->read_vmcoreinfo = vmcoreinfo_read_from_memory; > + pc->read_vmcoreinfo = vmcoreinfo_read_string; > break; > } > } > diff --git a/netdump.c b/netdump.c > index 69100a9..c7ff009 100644 > --- a/netdump.c > +++ b/netdump.c > @@ -111,14 +111,6 @@ map_cpus_to_prstatus(void) > FREEBUF(nt_ptr); > } > > -/** > - * Check if vmcoreinfo in vmcore is missing/empty > - */ > -static bool is_netdump_vmcoreinfo_empty(void) > -{ > - return (nd->size_vmcoreinfo == 0); > -} > - > /* > * Determine whether a file is a netdump/diskdump/kdump creation, > * and if TRUE, initialize the vmcore_data structure. > @@ -472,17 +464,6 @@ is_netdump(char *file, ulong source_query) > > pc->read_vmcoreinfo = vmcoreinfo_read_string; > > - /* > - * vmcoreinfo can be empty in case of dump collected via virsh-dump > - * > - * check if vmcoreinfo is not available in vmcore, and try to read > - * the vmcoreinfo from memory, using "vmcoreinfo_data" symbol > - */ > - if (is_netdump_vmcoreinfo_empty()) { > - error(WARNING, "vmcoreinfo is empty, will read from symbols\n"); > - pc->read_vmcoreinfo = vmcoreinfo_read_from_memory; > - } > - > if ((source_query == KDUMP_LOCAL) && > (pc->flags2 & GET_OSRELEASE)) > kdump_get_osrelease(); > -- > 2.47.0