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

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.

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