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Subject[Patch 4/4][crash] Recognise elf-note of type NT_NOCOREDUMP before vmcore analysis
The kernel might have added a new elf-note of type NT_NOCOREDUMP for various
reasons. This patch teaches crash tool to look for the same inside a vmcore
before further analysis. If present, display the error description and exit
early.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
---
netdump.c | 136 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
1 files changed, 131 insertions(+), 5 deletions(-)

diff --git a/netdump.c b/netdump.c
index 1e9960c..3b4edec 100644
--- a/netdump.c
+++ b/netdump.c
@@ -95,6 +95,74 @@ map_cpus_to_prstatus(void)
}

/*
+ * Temporary definition of new elf-note type for compilation purposes.
+ * Not required when run on a new kernel containing this definition.
+ */
+#define NT_NOCOREDUMP 21
+
+/*
+ * Function to verify if the vmcore contains and elf-note of type NT_NOCOREDUMP.
+ * The kernel adds such an elf-note when it is known that the crash is
+ * triggered due to a reason that does not need analysis of the entire kernel
+ * memory dump (e.g. crash triggered due to a faulty memory DIMM).
+ */
+static void
+has_nt_nocoredump(void *note_ptr, unsigned long size_note)
+{
+ Elf32_Nhdr *note32 = NULL;
+ Elf64_Nhdr *note64 = NULL;
+ size_t tot, len = 0;
+ int num = 0;
+
+ for (tot = 0; tot < size_note; tot += len) {
+ if (machine_type("X86_64")) {
+ note64 = note_ptr + tot;
+ /*
+ * If vmcore is generated due to fatal hardware
+ * errors (such as Machine Check Exception, we only have
+ * a 'slim' crashdump. Don't analyse further, inform the
+ * user about it and exit.
+ */
+ if (note64->n_type == NT_NOCOREDUMP) {
+ fprintf(fp, "\"System crashed due to a hardware"
+ " memory error. No coredump"
+ " available.\"\n");
+
+ /* Do we have an accompanying error message? */
+ if (note64->n_descsz == 0)
+ goto exit;
+ fprintf(fp,"Nocoredump Reason: %s",
+ (char *)note64 + sizeof(Elf64_Nhdr));
+ }
+
+ len = sizeof(Elf64_Nhdr);
+ len = roundup(len + note64->n_namesz, 4);
+ len = roundup(len + note64->n_descsz, 4);
+ } else if (machine_type("X86")) {
+ note32 = note_ptr + tot;
+ if (note32->n_type == NT_NOCOREDUMP) {
+ fprintf(fp, "\"System crashed due to a hardware"
+ " memory error. No coredump"
+ " available.\"\n");
+
+ /* Do we have an accompanying error message? */
+ if (note32->n_descsz == 0)
+ goto exit;
+
+ fprintf(fp,"Nocoredump Reason: %s",
+ (char *)note32 + sizeof(Elf32_Nhdr));
+exit:
+ clean_exit(0);
+ }
+
+ len = sizeof(Elf32_Nhdr);
+ len = roundup(len + note32->n_namesz, 4);
+ len = roundup(len + note32->n_descsz, 4);
+ }
+ }
+}
+
+/*
* Determine whether a file is a netdump/diskdump/kdump creation,
* and if TRUE, initialize the vmcore_data structure.
*/
@@ -103,12 +171,12 @@ is_netdump(char *file, ulong source_query)
{
int i, fd, swap;
Elf32_Ehdr *elf32;
- Elf32_Phdr *load32;
+ Elf32_Phdr *load32, *myload32;
Elf64_Ehdr *elf64;
- Elf64_Phdr *load64;
+ Elf64_Phdr *load64, *myload64;
char eheader[MIN_NETDUMP_ELF_HEADER_SIZE];
char buf[BUFSIZE];
- size_t size, len, tot;
+ size_t size, mysize, len, tot;
Elf32_Off offset32;
Elf64_Off offset64;
ulong tmp_flags;
@@ -195,7 +263,10 @@ is_netdump(char *file, ulong source_query)

load32 = (Elf32_Phdr *)
&eheader[sizeof(Elf32_Ehdr)+sizeof(Elf32_Phdr)];
- size = (size_t)load32->p_offset;
+ myload32 = (Elf32_Phdr *)
+ &eheader[sizeof(Elf32_Ehdr)];
+
+ size = (size_t)myload32->p_offset;

if ((load32->p_offset & (MIN_PAGE_SIZE-1)) &&
(load32->p_align == 0))
@@ -249,7 +320,10 @@ is_netdump(char *file, ulong source_query)

load64 = (Elf64_Phdr *)
&eheader[sizeof(Elf64_Ehdr)+sizeof(Elf64_Phdr)];
- size = (size_t)load64->p_offset;
+ myload64 = (Elf64_Phdr *)
+ &eheader[sizeof(Elf64_Ehdr)];
+
+ size = (size_t)myload64->p_offset;
if ((load64->p_offset & (MIN_PAGE_SIZE-1)) &&
(load64->p_align == 0))
tmp_flags |= KDUMP_ELF64;
@@ -362,6 +436,58 @@ is_netdump(char *file, ulong source_query)
&nd->elf_header[sizeof(Elf64_Ehdr)];
nd->load64 = (Elf64_Phdr *)
&nd->elf_header[sizeof(Elf64_Ehdr)+sizeof(Elf64_Phdr)];
+ /*
+ * Find out if there exists an elf-note of type NT_NOCOREDUMP.
+ * If so, exit early from crash analysis after displaying the
+ * description string.
+ *
+ * Allocate a temporary buffer to store the PT_NOTE section and
+ * loop through them to look for NT_NOCOREDUMP.
+ */
+ for (i = 0; i < elf64->e_phnum; i++, myload64++) {
+ mysize += myload64->p_memsz;
+ if (myload64->p_type == PT_NOTE) {
+ break;
+ }
+ }
+
+ if (mysize == 0) {
+ fprintf(stderr, "No PT_NOTE section found\n");
+ clean_exit(1);
+ }
+
+ /*
+ * Size of the buffer should accommodate the Elf_Ehdr, Elf_Phdr
+ * and all sections upto the first PT_NOTE.
+ */
+ mysize += size;
+ tmp_elf_header = realloc(tmp_elf_header, mysize);
+ if (tmp_elf_header == NULL) {
+ fprintf(stderr, "cannot malloc notes buffer\n");
+ clean_exit(1);
+ }
+ if (FLAT_FORMAT()) {
+ if (!read_flattened_format(fd, 0, tmp_elf_header, mysize)) {
+ free(tmp_elf_header);
+ goto bailout;
+ }
+ } else {
+ if (lseek(fd, 0, SEEK_SET) != 0) {
+ sprintf(buf, "%s: lseek", file);
+ perror(buf);
+ goto bailout;
+ }
+ if (read(fd, tmp_elf_header, mysize) != mysize) {
+ sprintf(buf, "%s: read", file);
+ perror(buf);
+ free(tmp_elf_header);
+ goto bailout;
+ }
+ }
+
+ has_nt_nocoredump((char *)tmp_elf_header + myload64->p_offset,
+ myload64->p_memsz);
+
if (DUMPFILE_FORMAT(nd->flags) == NETDUMP_ELF64)
nd->page_size = (uint)nd->load64->p_align;
dump_Elf64_Ehdr(nd->elf64);
--
1.7.4.1


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