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Re: [PATCH 1/7] dump: Introduce shdr_num to decrease complexity

From: Janosch Frank
Subject: Re: [PATCH 1/7] dump: Introduce shdr_num to decrease complexity
Date: Tue, 8 Mar 2022 14:16:12 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 
On 3/1/22 15:42, Marc-André Lureau wrote:

Hi

On Tue, Mar 1, 2022 at 6:33 PM Janosch Frank <frankja@linux.ibm.com> wrote:


Let's move from a boolean to a int variable which will later enable us
to store the number of sections that are in the dump file.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
---
  dump/dump.c           | 43 ++++++++++++++++++-------------------------
  include/sysemu/dump.h |  2 +-
  2 files changed, 19 insertions(+), 26 deletions(-)

diff --git a/dump/dump.c b/dump/dump.c
index a84d8b1598..6696d9819a 100644
--- a/dump/dump.c
+++ b/dump/dump.c
@@ -139,12 +139,12 @@ static void write_elf64_header(DumpState *s, Error
**errp)
      elf_header.e_phoff = cpu_to_dump64(s, sizeof(Elf64_Ehdr));
      elf_header.e_phentsize = cpu_to_dump16(s, sizeof(Elf64_Phdr));
      elf_header.e_phnum = cpu_to_dump16(s, s->phdr_num);
-    if (s->have_section) {
+    if (s->shdr_num) {
          uint64_t shoff = sizeof(Elf64_Ehdr) + sizeof(Elf64_Phdr) *
s->sh_info;

          elf_header.e_shoff = cpu_to_dump64(s, shoff);
          elf_header.e_shentsize = cpu_to_dump16(s, sizeof(Elf64_Shdr));
-        elf_header.e_shnum = cpu_to_dump16(s, 1);
+        elf_header.e_shnum = cpu_to_dump16(s, s->shdr_num);
      }

      ret = fd_write_vmcore(&elf_header, sizeof(elf_header), s);
@@ -170,12 +170,12 @@ static void write_elf32_header(DumpState *s, Error
**errp)
      elf_header.e_phoff = cpu_to_dump32(s, sizeof(Elf32_Ehdr));
      elf_header.e_phentsize = cpu_to_dump16(s, sizeof(Elf32_Phdr));
      elf_header.e_phnum = cpu_to_dump16(s, s->phdr_num);
-    if (s->have_section) {
+    if (s->shdr_num) {
          uint32_t shoff = sizeof(Elf32_Ehdr) + sizeof(Elf32_Phdr) *
s->sh_info;

          elf_header.e_shoff = cpu_to_dump32(s, shoff);
          elf_header.e_shentsize = cpu_to_dump16(s, sizeof(Elf32_Shdr));
-        elf_header.e_shnum = cpu_to_dump16(s, 1);
+        elf_header.e_shnum = cpu_to_dump16(s, s->shdr_num);
      }

      ret = fd_write_vmcore(&elf_header, sizeof(elf_header), s);
@@ -482,7 +482,7 @@ static void write_elf_loads(DumpState *s, Error **errp)
      uint32_t max_index;
      Error *local_err = NULL;

-    if (s->have_section) {
+    if (s->shdr_num) {
          max_index = s->sh_info;
      } else {
          max_index = s->phdr_num;
@@ -567,7 +567,7 @@ static void dump_begin(DumpState *s, Error **errp)
          }

          /* write section to vmcore */
-        if (s->have_section) {
+        if (s->shdr_num) {
              write_elf_section(s, 1, &local_err);
              if (local_err) {
                  error_propagate(errp, local_err);
@@ -597,7 +597,7 @@ static void dump_begin(DumpState *s, Error **errp)
          }

          /* write section to vmcore */
-        if (s->have_section) {
+        if (s->shdr_num) {
              write_elf_section(s, 0, &local_err);
              if (local_err) {
                  error_propagate(errp, local_err);
@@ -1818,11 +1818,12 @@ static void dump_init(DumpState *s, int fd, bool
has_format,
       */
      s->phdr_num = 1; /* PT_NOTE */
      if (s->list.num < UINT16_MAX - 2) {
+        s->shdr_num = 0;
          s->phdr_num += s->list.num;
-        s->have_section = false;
      } else {
-        s->have_section = true;
+        /* sh_info of section 0 holds the real number of phdrs */



...



          s->phdr_num = PN_XNUM;
+        s->shdr_num = 1;
          s->sh_info = 1; /* PT_NOTE */

          /* the type of shdr->sh_info is uint32_t, so we should avoid
overflow */
@@ -1834,23 +1835,15 @@ static void dump_init(DumpState *s, int fd, bool
has_format,
      }

      if (s->dump_info.d_class == ELFCLASS64) {
-        if (s->have_section) {
-            s->memory_offset = sizeof(Elf64_Ehdr) +
-                               sizeof(Elf64_Phdr) * s->sh_info +
-                               sizeof(Elf64_Shdr) + s->note_size;
-        } else {
-            s->memory_offset = sizeof(Elf64_Ehdr) +
-                               sizeof(Elf64_Phdr) * s->phdr_num +
s->note_size;
-        }
+        s->memory_offset = sizeof(Elf64_Ehdr) +
+                           sizeof(Elf64_Phdr) * s->sh_info +



The change "removing/replacing sizeof(Elf64_Phdr) * s->phdr_num by *
s->sh_info" should be done as a preliminary step, with more comments.
I had another look at this and this patch won't work without the next patch anyway. I'll try to recombine and split the patches in a way that makes this easier to read. 




+                           sizeof(Elf64_Shdr) * s->shdr_num +

+                           s->note_size;
      } else {
-        if (s->have_section) {
-            s->memory_offset = sizeof(Elf32_Ehdr) +
-                               sizeof(Elf32_Phdr) * s->sh_info +
-                               sizeof(Elf32_Shdr) + s->note_size;
-        } else {
-            s->memory_offset = sizeof(Elf32_Ehdr) +
-                               sizeof(Elf32_Phdr) * s->phdr_num +
s->note_size;
-        }
+        s->memory_offset = sizeof(Elf32_Ehdr) +
+                           sizeof(Elf32_Phdr) * s->sh_info +
+                           sizeof(Elf32_Shdr) * s->shdr_num +
+                           s->note_size;
      }

      return;
diff --git a/include/sysemu/dump.h b/include/sysemu/dump.h
index 250143cb5a..854341da0d 100644
--- a/include/sysemu/dump.h
+++ b/include/sysemu/dump.h
@@ -155,8 +155,8 @@ typedef struct DumpState {
      ArchDumpInfo dump_info;
      MemoryMappingList list;
      uint16_t phdr_num;
+    uint32_t shdr_num;
      uint32_t sh_info;
-    bool have_section;
      bool resume;
      bool detached;
      ssize_t note_size;
--
2.32.0
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