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Re: [PATCH v5 12/18] dump/dump: Add section string table support

From: Janosch Frank
Subject: Re: [PATCH v5 12/18] dump/dump: Add section string table support
Date: Tue, 30 Aug 2022 16:02:28 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0

On 8/30/22 13:35, Steffen Eiden wrote:
Hi Janosch,

On 8/11/22 14:11, Janosch Frank wrote:
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           | 71 +++++++++++++++++++++++++++++++++++++++++++
   include/sysemu/dump.h |  4 +++
   2 files changed, 75 insertions(+)

diff --git a/dump/dump.c b/dump/dump.c
index 31eb20108c..0d6dbf453a 100644
--- a/dump/dump.c
+++ b/dump/dump.c
[ snip ]
+static void prepare_elf_section_hdr_string(DumpState *s, void *buff)
+    Elf32_Shdr shdr32;
+    Elf64_Shdr shdr64;
+    int shdr_size;
+    void *shdr;
+    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"));
I think you mixed up .strtab and .shstrtab here.
'.shstrtab' should be used here.

The ELF specs define bots as follows (from man 5 elf) :

                This section holds section names.  This section is of type
                SHT_STRTAB.  No attribute types are used.

                This section holds strings, most commonly the strings that
                represent the names associated with symbol table entries.
                If the file has a loadable segment that includes the
                symbol string table, the section's attributes will include
                the SHF_ALLOC bit.  Otherwise, the bit will be off.  This
                section is of type SHT_STRTAB.

However, the name lookup works, as you correctly specified that this
section holds the section header names via the 'e_shstrndx' field in the
elf header.

We can make this a shstrtab only strtab since that's effectively what it does right now. It annoys me that we'll need a second strtab if we ever want to name other structures. Or at least we'll need special handling.

+        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);
Also, with your patches the dump output places the headers in this ordering:
[elf hdr]
[section hdrs]
[program hdrs]

**normally** program hdrs are placed before section hdrs,
but this is just a convention IIRC.

I don't see why this should be a problem, that's what the offsets are for.


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