[PATCH v4 11/17] dump/dump: Add section string table support

[Janosch Frank <frankja@linux.ibm.com>]

As sections don't have a type like the notes do we need another way to
determine their contents. The string table allows us to assign each
section an identification string which architectures can then use to
tag their sections with.

There will be no string table if the architecture doesn't add custom
sections which are introduced in a following patch.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
---
 dump/dump.c           | 81 ++++++++++++++++++++++++++++++++++++++++++-
 include/sysemu/dump.h |  1 +
 2 files changed, 81 insertions(+), 1 deletion(-)

diff --git a/dump/dump.c b/dump/dump.c
index 3cf846d0a0..298a1e923f 100644
--- a/dump/dump.c
+++ b/dump/dump.c
@@ -99,6 +99,7 @@ static int dump_cleanup(DumpState *s)
     close(s->fd);
     g_free(s->guest_note);
     g_free(s->elf_header);
+    g_array_unref(s->string_table_buf);
     s->guest_note = NULL;
     if (s->resume) {
         if (s->detached) {
@@ -357,21 +358,72 @@ static size_t prepare_elf_section_hdr_zero(DumpState *s)
     return dump_is_64bit(s) ? sizeof(Elf64_Shdr) : sizeof(Elf32_Shdr);
 }
 
+static void write_elf_section_hdr_string(DumpState *s, void *buff)
+{
+    Elf32_Shdr shdr32;
+    Elf64_Shdr shdr64;
+    int shdr_size;
+    void *shdr = buff;
+
+    if (dump_is_64bit(s)) {
+        shdr_size = sizeof(Elf64_Shdr);
+        memset(&shdr64, 0, shdr_size);
+        shdr64.sh_type = SHT_STRTAB;
+        shdr64.sh_offset = s->section_offset + s->elf_section_data_size;
+        shdr64.sh_name = s->string_table_buf->len;
+        g_array_append_vals(s->string_table_buf, ".strtab", sizeof(".strtab"));
+        shdr64.sh_size = s->string_table_buf->len;
+        shdr = &shdr64;
+    } else {
+        shdr_size = sizeof(Elf32_Shdr);
+        memset(&shdr32, 0, shdr_size);
+        shdr32.sh_type = SHT_STRTAB;
+        shdr32.sh_offset = s->section_offset + s->elf_section_data_size;
+        shdr32.sh_name = s->string_table_buf->len;
+        g_array_append_vals(s->string_table_buf, ".strtab", sizeof(".strtab"));
+        shdr32.sh_size = s->string_table_buf->len;
+        shdr = &shdr32;
+    }
+
+    memcpy(buff, shdr, shdr_size);
+}
+
 static void prepare_elf_section_hdrs(DumpState *s)
 {
     size_t len, sizeof_shdr;
+    Elf64_Ehdr *hdr64 = s->elf_header;
+    Elf32_Ehdr *hdr32 = s->elf_header;
+    void *buff_hdr;
 
     /*
      * Section ordering:
      * - HDR zero (if needed)
+     * - String table hdr
      */
     sizeof_shdr = dump_is_64bit(s) ? sizeof(Elf64_Shdr) : sizeof(Elf32_Shdr);
     len = sizeof_shdr * s->shdr_num;
     s->elf_section_hdrs = g_malloc0(len);
+    buff_hdr = s->elf_section_hdrs;
 
     /* Write special section first */
     if (s->phdr_num == PN_XNUM) {
         prepare_elf_section_hdr_zero(s);
+        buff_hdr += sizeof_shdr;
+    }
+
+    if (s->shdr_num < 2) {
+        return;
+    }
+
+    /*
+     * String table needs to be last section since strings are added
+     * via arch_sections_write_hdr().
+     */
+    write_elf_section_hdr_string(s, buff_hdr);
+    if (dump_is_64bit(s)) {
+        hdr64->e_shstrndx = cpu_to_dump16(s, s->shdr_num - 1);
+    } else {
+        hdr32->e_shstrndx = cpu_to_dump16(s, s->shdr_num - 1);
     }
 }
 
@@ -401,11 +453,18 @@ static void write_elf_sections(DumpState *s, Error **errp)
 {
     int ret;
 
-    /* Write section zero */
+    /* Write section zero and arch sections */
     ret = fd_write_vmcore(s->elf_section_data, s->elf_section_data_size, s);
     if (ret < 0) {
         error_setg_errno(errp, -ret, "dump: failed to write section data");
     }
+
+    /* Write string table data */
+    ret = fd_write_vmcore(s->string_table_buf->data,
+                          s->string_table_buf->len, s);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret, "dump: failed to write string table data");
+    }
 }
 
 static void write_data(DumpState *s, void *buf, int length, Error **errp)
@@ -713,6 +772,7 @@ static void create_vmcore(DumpState *s, Error **errp)
         return;
     }
 
+    /* Iterate over memory and dump it to file */
     dump_iterate(s, errp);
     if (*errp) {
         return;
@@ -1695,6 +1755,13 @@ static void dump_init(DumpState *s, int fd, bool has_format,
     s->has_filter = has_filter;
     s->begin = begin;
     s->length = length;
+    /* First index is 0, it's the special null name */
+    s->string_table_buf = g_array_new(FALSE, TRUE, 1);
+    /*
+     * Allocate the null name, due to the clearing option set to true
+     * it will be 0.
+     */
+    g_array_set_size(s->string_table_buf, 1);
 
     memory_mapping_list_init(&s->list);
 
@@ -1855,6 +1922,18 @@ static void dump_init(DumpState *s, int fd, bool has_format,
         }
     }
 
+    /*
+     * calculate shdr_num and elf_section_data_size so we know the offsets and
+     * sizes of all parts.
+     *
+     * If phdr_num overflowed we have at least one section header
+     * More sections/hdrs can be added by the architectures
+     */
+    if (s->shdr_num > 1) {
+        /* Reserve the string table */
+        s->shdr_num += 1;
+    }
+
     tmp = (s->phdr_num == PN_XNUM) ? s->sh_info : s->phdr_num;
     if (dump_is_64bit(s)) {
         s->shdr_offset = sizeof(Elf64_Ehdr);
diff --git a/include/sysemu/dump.h b/include/sysemu/dump.h
index 696e6c67d6..299b611180 100644
--- a/include/sysemu/dump.h
+++ b/include/sysemu/dump.h
@@ -178,6 +178,7 @@ typedef struct DumpState {
     void *elf_section_hdrs;
     uint64_t elf_section_data_size;
     void *elf_section_data;
+    GArray *string_table_buf;  /* String table section */
 
     uint8_t *note_buf;          /* buffer for notes */
     size_t note_buf_offset;     /* the writing place in note_buf */
-- 
2.34.1