[1/5] dump: Allocate header

Commit Message

Janosch Frank March 10, 2022, 11:16 a.m. UTC

Allocating the header lets us write it at a later time and hence also
allows us to change section and segment table offsets until we
finally write it.

Signed-off-by: Janosch Frank <[e-mail]>
---
 dump/dump.c           | 115 ++++++++++++++++++++++--------------------
 include/sysemu/dump.h |   1 +
 2 files changed, 62 insertions(+), 54 deletions(-)

Comments

Richard Henderson March 11, 2022, 8:06 p.m. UTC | #1

On 3/10/22 03:16, Janosch Frank wrote:
> Allocating the header lets us write it at a later time and hence also
> allows us to change section and segment table offsets until we
> finally write it.
> 
> Signed-off-by: Janosch Frank <[e-mail]>
> ---
>   dump/dump.c           | 115 ++++++++++++++++++++++--------------------
>   include/sysemu/dump.h |   1 +
>   2 files changed, 62 insertions(+), 54 deletions(-)

You're collecting the important pieces that go into the header separately (phdr_offset, 
phdr_num, etc), and you can certainly change those as you go along.  But I don't see the 
point of allocating the ehdr early.  I think you should create it and write it out 
immediately.


r~

Patch

diff --git a/dump/dump.c b/dump/dump.c
index ae8ec527de..88343d7486 100644
--- a/dump/dump.c
+++ b/dump/dump.c
@@ -99,6 +99,7 @@  static int dump_cleanup(DumpState *s)
     memory_mapping_list_free(&s->list);
     close(s->fd);
     g_free(s->guest_note);
+    g_free(s->elf_header);
     s->guest_note = NULL;
     if (s->resume) {
         if (s->detached) {
@@ -127,63 +128,47 @@  static int fd_write_vmcore(const void *buf, size_t size, void *opaque)
     return 0;
 }
 
-static void write_elf64_header(DumpState *s, Error **errp)
+static void prepare_elf64_header(DumpState *s)
 {
-    uint16_t phnum = s->phdr_num >= PN_XNUM ? PN_XNUM : s->phdr_num;
-    Elf64_Ehdr elf_header;
-    int ret;
+    Elf64_Ehdr *elf_header = s->elf_header;
 
-    memset(&elf_header, 0, sizeof(Elf64_Ehdr));
-    memcpy(&elf_header, ELFMAG, SELFMAG);
-    elf_header.e_ident[EI_CLASS] = ELFCLASS64;
-    elf_header.e_ident[EI_DATA] = s->dump_info.d_endian;
-    elf_header.e_ident[EI_VERSION] = EV_CURRENT;
-    elf_header.e_type = cpu_to_dump16(s, ET_CORE);
-    elf_header.e_machine = cpu_to_dump16(s, s->dump_info.d_machine);
-    elf_header.e_version = cpu_to_dump32(s, EV_CURRENT);
-    elf_header.e_ehsize = cpu_to_dump16(s, sizeof(elf_header));
-    elf_header.e_phoff = cpu_to_dump64(s, s->phdr_offset);
-    elf_header.e_phentsize = cpu_to_dump16(s, sizeof(Elf64_Phdr));
-    elf_header.e_phnum = cpu_to_dump16(s, phnum);
+    memcpy(elf_header, ELFMAG, SELFMAG);
+    elf_header->e_ident[EI_CLASS] = ELFCLASS64;
+    elf_header->e_ident[EI_DATA] = s->dump_info.d_endian;
+    elf_header->e_ident[EI_VERSION] = EV_CURRENT;
+    elf_header->e_type = cpu_to_dump16(s, ET_CORE);
+    elf_header->e_machine = cpu_to_dump16(s, s->dump_info.d_machine);
+    elf_header->e_version = cpu_to_dump32(s, EV_CURRENT);
+    elf_header->e_ehsize = cpu_to_dump16(s, sizeof(*elf_header));
+    elf_header->e_phoff = cpu_to_dump64(s, s->phdr_offset);
+    elf_header->e_phentsize = cpu_to_dump16(s, sizeof(Elf64_Phdr));
+    elf_header->e_phnum = cpu_to_dump16(s, s->phdr_num);
     if (s->shdr_num) {
-        elf_header.e_shoff = cpu_to_dump64(s, s->shdr_offset);
-        elf_header.e_shentsize = cpu_to_dump16(s, sizeof(Elf64_Shdr));
-        elf_header.e_shnum = cpu_to_dump16(s, s->shdr_num);
-    }
-
-    ret = fd_write_vmcore(&elf_header, sizeof(elf_header), s);
-    if (ret < 0) {
-        error_setg_errno(errp, -ret, "dump: failed to write elf header");
+        elf_header->e_shoff = cpu_to_dump64(s, s->shdr_offset);
+        elf_header->e_shentsize = cpu_to_dump16(s, sizeof(Elf64_Shdr));
+        elf_header->e_shnum = cpu_to_dump16(s, s->shdr_num);
     }
 }
 
-static void write_elf32_header(DumpState *s, Error **errp)
+static void prepare_elf32_header(DumpState *s)
 {
-    uint16_t phnum = s->phdr_num >= PN_XNUM ? PN_XNUM : s->phdr_num;
-    Elf32_Ehdr elf_header;
-    int ret;
+    Elf32_Ehdr *elf_header = s->elf_header;
 
-    memset(&elf_header, 0, sizeof(Elf32_Ehdr));
-    memcpy(&elf_header, ELFMAG, SELFMAG);
-    elf_header.e_ident[EI_CLASS] = ELFCLASS32;
-    elf_header.e_ident[EI_DATA] = s->dump_info.d_endian;
-    elf_header.e_ident[EI_VERSION] = EV_CURRENT;
-    elf_header.e_type = cpu_to_dump16(s, ET_CORE);
-    elf_header.e_machine = cpu_to_dump16(s, s->dump_info.d_machine);
-    elf_header.e_version = cpu_to_dump32(s, EV_CURRENT);
-    elf_header.e_ehsize = cpu_to_dump16(s, sizeof(elf_header));
-    elf_header.e_phoff = cpu_to_dump32(s, s->phdr_offset);
-    elf_header.e_phentsize = cpu_to_dump16(s, sizeof(Elf32_Phdr));
-    elf_header.e_phnum = cpu_to_dump16(s, phnum);
+    memcpy(elf_header, ELFMAG, SELFMAG);
+    elf_header->e_ident[EI_CLASS] = ELFCLASS32;
+    elf_header->e_ident[EI_DATA] = s->dump_info.d_endian;
+    elf_header->e_ident[EI_VERSION] = EV_CURRENT;
+    elf_header->e_type = cpu_to_dump16(s, ET_CORE);
+    elf_header->e_machine = cpu_to_dump16(s, s->dump_info.d_machine);
+    elf_header->e_version = cpu_to_dump32(s, EV_CURRENT);
+    elf_header->e_ehsize = cpu_to_dump16(s, sizeof(*elf_header));
+    elf_header->e_phoff = cpu_to_dump32(s, s->phdr_offset);
+    elf_header->e_phentsize = cpu_to_dump16(s, sizeof(Elf32_Phdr));
+    elf_header->e_phnum = cpu_to_dump16(s, s->phdr_num);
     if (s->shdr_num) {
-        elf_header.e_shoff = cpu_to_dump32(s, s->shdr_offset);
-        elf_header.e_shentsize = cpu_to_dump16(s, sizeof(Elf32_Shdr));
-        elf_header.e_shnum = cpu_to_dump16(s, s->shdr_num);
-    }
-
-    ret = fd_write_vmcore(&elf_header, sizeof(elf_header), s);
-    if (ret < 0) {
-        error_setg_errno(errp, -ret, "dump: failed to write elf header");
+        elf_header->e_shoff = cpu_to_dump32(s, s->shdr_offset);
+        elf_header->e_shentsize = cpu_to_dump16(s, sizeof(Elf32_Shdr));
+        elf_header->e_shnum = cpu_to_dump16(s, s->shdr_num);
     }
 }
 
@@ -524,6 +509,26 @@  static void write_elf_notes(DumpState *s, Error **errp)
     }
 }
 
+static void prepare_elf_header(DumpState *s)
+{
+    if (dump_is_64bit(s)) {
+        prepare_elf64_header(s);
+    } else {
+        prepare_elf32_header(s);
+    }
+}
+
+static void write_elf_header(DumpState *s, Error **errp)
+{
+    size_t size = dump_is_64bit(s) ? sizeof(Elf64_Ehdr) : sizeof(Elf32_Ehdr);
+    int ret;
+
+    ret = fd_write_vmcore(s->elf_header, size, s);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret, "dump: failed to write elf header");
+    }
+}
+
 /* write elf header, PT_NOTE and elf note to vmcore. */
 static void dump_begin(DumpState *s, Error **errp)
 {
@@ -553,12 +558,11 @@  static void dump_begin(DumpState *s, Error **errp)
      * vmcore.
      */
 
-    /* write elf header to vmcore */
-    if (dump_is_64bit(s)) {
-        write_elf64_header(s, errp);
-    } else {
-        write_elf32_header(s, errp);
-    }
+    /* Write elf header to buffer */
+    prepare_elf_header(s);
+
+    /* Start to write stuff into files*/
+    write_elf_header(s, errp);
     if (*errp) {
         return;
     }
@@ -1683,6 +1687,9 @@  static void dump_init(DumpState *s, int fd, bool has_format,
         goto cleanup;
     }
 
+    s->elf_header = g_malloc0(dump_is_64bit(s) ?
+                              sizeof(Elf64_Ehdr) : sizeof(Elf32_Ehdr));
+
     /*
      * The goal of this block is to (a) update the previously guessed
      * phys_base, (b) copy the guest note out of the guest.
diff --git a/include/sysemu/dump.h b/include/sysemu/dump.h
index ffc2ea1072..9c4a83156b 100644
--- a/include/sysemu/dump.h
+++ b/include/sysemu/dump.h
@@ -172,6 +172,7 @@  typedef struct DumpState {
     int64_t begin;
     int64_t length;
 
+    void *elf_header;
     uint8_t *note_buf;          /* buffer for notes */
     size_t note_buf_offset;     /* the writing place in note_buf */
     uint32_t nr_cpus;           /* number of guest's cpu */