elf: allow for absence of dynstr

.dynstr doesn't need to be present if there are no dynamic strings. - handle section index 0 in read::elf::SectionTable::strings - don't require .dynstr when writing if there are no strings - don't print name of symbol index 0 in readobj example
gimli-rs · Mar 18, 2024 · 5e225a2 · 5e225a2
1 parent 609f677
commit 5e225a2
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Showing 15 changed files with 68 additions and 48 deletions.
diff --git a/crates/examples/src/readobj/elf.rs b/crates/examples/src/readobj/elf.rs
@@ -398,11 +398,15 @@ fn print_section_symbols<Elf: FileHeader>(
         for (index, symbol) in symbols.iter().enumerate() {
             p.group("Symbol", |p| {
                 p.field("Index", index);
-                p.field_string(
-                    "Name",
-                    symbol.st_name(endian),
-                    symbol.name(endian, symbols.strings()),
-                );
+                if index == 0 {
+                    p.field_hex("Name", symbol.st_name(endian));
+                } else {
+                    p.field_string(
+                        "Name",
+                        symbol.st_name(endian),
+                        symbol.name(endian, symbols.strings()),
+                    );
+                }
                 if let Some(versions) = versions.as_ref() {
                     let version_index = versions.version_index(endian, index);
                     print_version(p, Some(versions), version_index);
@@ -511,6 +515,10 @@ fn print_rel_symbol<Elf: FileHeader>(
     symbols: Option<SymbolTable<'_, Elf>>,
     sym: u32,
 ) {
+    if sym == 0 {
+        p.field_hex("Symbol", sym);
+        return;
+    }
     let name = symbols.and_then(|symbols| {
         symbols
             .symbol(sym as usize)

diff --git a/crates/examples/testfiles/elf/base-aarch64.o.readobj b/crates/examples/testfiles/elf/base-aarch64.o.readobj
@@ -167,7 +167,7 @@ SectionHeader {
     EntrySize: 0x18
     Symbol {
         Index: 0
-        Name: "" (0x0)
+        Name: 0x0
         Value: 0x0
         Size: 0x0
         Type: STT_NOTYPE (0x0)

diff --git a/crates/examples/testfiles/elf/base-aarch64.readobj b/crates/examples/testfiles/elf/base-aarch64.readobj
@@ -338,7 +338,7 @@ SectionHeader {
     EntrySize: 0x18
     Symbol {
         Index: 0
-        Name: "" (0x0)
+        Name: 0x0
         Version: VER_NDX_LOCAL (0x0)
         Value: 0x0
         Size: 0x0
@@ -559,37 +559,37 @@ SectionHeader {
     Relocation {
         Offset: 0x10D80
         Type: R_AARCH64_RELATIVE (0x403)
-        Symbol: "" (0x0)
+        Symbol: 0x0
         Addend: 0x720
     }
     Relocation {
         Offset: 0x10D88
         Type: R_AARCH64_RELATIVE (0x403)
-        Symbol: "" (0x0)
+        Symbol: 0x0
         Addend: 0x6D8
     }
     Relocation {
         Offset: 0x10FC8
         Type: R_AARCH64_RELATIVE (0x403)
-        Symbol: "" (0x0)
+        Symbol: 0x0
         Addend: 0x7C8
     }
     Relocation {
         Offset: 0x10FE8
         Type: R_AARCH64_RELATIVE (0x403)
-        Symbol: "" (0x0)
+        Symbol: 0x0
         Addend: 0x748
     }
     Relocation {
         Offset: 0x10FF0
         Type: R_AARCH64_RELATIVE (0x403)
-        Symbol: "" (0x0)
+        Symbol: 0x0
         Addend: 0x724
     }
     Relocation {
         Offset: 0x11008
         Type: R_AARCH64_RELATIVE (0x403)
-        Symbol: "" (0x0)
+        Symbol: 0x0
         Addend: 0x11008
     }
     Relocation {
@@ -971,7 +971,7 @@ SectionHeader {
     EntrySize: 0x18
     Symbol {
         Index: 0
-        Name: "" (0x0)
+        Name: 0x0
         Value: 0x0
         Size: 0x0
         Type: STT_NOTYPE (0x0)

diff --git a/crates/examples/testfiles/elf/base-mips64el.o.readobj b/crates/examples/testfiles/elf/base-mips64el.o.readobj
@@ -269,7 +269,7 @@ SectionHeader {
     EntrySize: 0x18
     Symbol {
         Index: 0
-        Name: "" (0x0)
+        Name: 0x0
         Value: 0x0
         Size: 0x0
         Type: STT_NOTYPE (0x0)

diff --git a/crates/examples/testfiles/elf/base-mips64el.readobj b/crates/examples/testfiles/elf/base-mips64el.readobj
@@ -442,7 +442,7 @@ SectionHeader {
     EntrySize: 0x18
     Symbol {
         Index: 0
-        Name: "" (0x0)
+        Name: 0x0
         Version: VER_NDX_LOCAL (0x0)
         Value: 0x0
         Size: 0x0
@@ -984,7 +984,7 @@ SectionHeader {
     EntrySize: 0x18
     Symbol {
         Index: 0
-        Name: "" (0x0)
+        Name: 0x0
         Value: 0x0
         Size: 0x0
         Type: STT_NOTYPE (0x0)

diff --git a/crates/examples/testfiles/elf/base.o.readobj b/crates/examples/testfiles/elf/base.o.readobj
@@ -197,7 +197,7 @@ SectionHeader {
     EntrySize: 0x18
     Symbol {
         Index: 0
-        Name: "" (0x0)
+        Name: 0x0
         Value: 0x0
         Size: 0x0
         Type: STT_NOTYPE (0x0)

diff --git a/crates/examples/testfiles/elf/base.readobj b/crates/examples/testfiles/elf/base.readobj
@@ -371,7 +371,7 @@ SectionHeader {
     EntrySize: 0x18
     Symbol {
         Index: 0
-        Name: "" (0x0)
+        Name: 0x0
         Version: VER_NDX_LOCAL (0x0)
         Value: 0x0
         Size: 0x0
@@ -547,19 +547,19 @@ SectionHeader {
     Relocation {
         Offset: 0x200DA8
         Type: R_X86_64_RELATIVE (0x8)
-        Symbol: "" (0x0)
+        Symbol: 0x0
         Addend: 0x670
     }
     Relocation {
         Offset: 0x200DB0
         Type: R_X86_64_RELATIVE (0x8)
-        Symbol: "" (0x0)
+        Symbol: 0x0
         Addend: 0x630
     }
     Relocation {
         Offset: 0x201008
         Type: R_X86_64_RELATIVE (0x8)
-        Symbol: "" (0x0)
+        Symbol: 0x0
         Addend: 0x201008
     }
     Relocation {
@@ -959,7 +959,7 @@ SectionHeader {
     EntrySize: 0x18
     Symbol {
         Index: 0
-        Name: "" (0x0)
+        Name: 0x0
         Value: 0x0
         Size: 0x0
         Type: STT_NOTYPE (0x0)

diff --git a/crates/examples/testfiles/elf/nostd-mipsel.o.readobj b/crates/examples/testfiles/elf/nostd-mipsel.o.readobj
@@ -227,7 +227,7 @@ SectionHeader {
     EntrySize: 0x10
     Symbol {
         Index: 0
-        Name: "" (0x0)
+        Name: 0x0
         Value: 0x0
         Size: 0x0
         Type: STT_NOTYPE (0x0)

diff --git a/crates/examples/testfiles/elf/nostd-mipsel.readobj b/crates/examples/testfiles/elf/nostd-mipsel.readobj
@@ -185,7 +185,7 @@ SectionHeader {
     EntrySize: 0x10
     Symbol {
         Index: 0
-        Name: "" (0x0)
+        Name: 0x0
         Value: 0x0
         Size: 0x0
         Type: STT_NOTYPE (0x0)

diff --git a/crates/rewrite/testfiles/elf/base.delete-symbol b/crates/rewrite/testfiles/elf/base.delete-symbol
@@ -211,7 +211,7 @@ SectionHeader {
     EntrySize: 0x18
     Symbol {
         Index: 0
-        Name: ""
+        Name: 0x0
         Version: VER_NDX_LOCAL (0x0)
         Value: 0x0
         Size: 0x0
@@ -583,7 +583,7 @@ SectionHeader {
     EntrySize: 0x18
     Symbol {
         Index: 0
-        Name: ""
+        Name: 0x0
         Value: 0x0
         Size: 0x0
         Type: STT_NOTYPE (0x0)

diff --git a/crates/rewrite/testfiles/elf/base.noop b/crates/rewrite/testfiles/elf/base.noop
@@ -371,7 +371,7 @@ SectionHeader {
     EntrySize: 0x18
     Symbol {
         Index: 0
-        Name: ""
+        Name: 0x0
         Version: VER_NDX_LOCAL (0x0)
         Value: 0x0
         Size: 0x0
@@ -547,19 +547,19 @@ SectionHeader {
     Relocation {
         Offset: 0x200DA8
         Type: R_X86_64_RELATIVE (0x8)
-        Symbol: ""
+        Symbol: 0x0
         Addend: 0x670
     }
     Relocation {
         Offset: 0x200DB0
         Type: R_X86_64_RELATIVE (0x8)
-        Symbol: ""
+        Symbol: 0x0
         Addend: 0x630
     }
     Relocation {
         Offset: 0x201008
         Type: R_X86_64_RELATIVE (0x8)
-        Symbol: ""
+        Symbol: 0x0
         Addend: 0x201008
     }
     Relocation {
@@ -959,7 +959,7 @@ SectionHeader {
     EntrySize: 0x18
     Symbol {
         Index: 0
-        Name: ""
+        Name: 0x0
         Value: 0x0
         Size: 0x0
         Type: STT_NOTYPE (0x0)

diff --git a/crates/rewrite/testfiles/elf/base.rename-symbol b/crates/rewrite/testfiles/elf/base.rename-symbol
@@ -222,7 +222,7 @@ SectionHeader {
     EntrySize: 0x18
     Symbol {
         Index: 0
-        Name: ""
+        Name: 0x0
         Version: VER_NDX_LOCAL (0x0)
         Value: 0x0
         Size: 0x0
@@ -605,7 +605,7 @@ SectionHeader {
     EntrySize: 0x18
     Symbol {
         Index: 0
-        Name: ""
+        Name: 0x0
         Value: 0x0
         Size: 0x0
         Type: STT_NOTYPE (0x0)

diff --git a/src/build/elf.rs b/src/build/elf.rs
@@ -1034,15 +1034,21 @@ impl<'data> Builder<'data> {
             return Err(Error::new(
                 ".symtab.shndx section is needed but not present",
             ));
+        } else if symtab_shndx_id.is_some() {
+            writer.require_symtab_shndx();
         }
         if strtab_id.is_none() && writer.strtab_needed() {
             return Err(Error::new(".strtab section is needed but not present"));
+        } else if strtab_id.is_some() {
+            writer.require_strtab();
         }
         if dynsym_id.is_none() && !out_dynsyms.is_empty() {
             return Err(Error::new(".dynsym section is needed but not present"));
         }
         if dynstr_id.is_none() && writer.dynstr_needed() {
             return Err(Error::new(".dynstr section is needed but not present"));
+        } else if dynstr_id.is_some() {
+            writer.require_dynstr();
         }
         if gnu_verdef_id.is_none() && verdef_count > 0 {
             return Err(Error::new(

diff --git a/src/read/elf/section.rs b/src/read/elf/section.rs
@@ -86,6 +86,7 @@ impl<'data, Elf: FileHeader, R: ReadRef<'data>> SectionTable<'data, Elf, R> {
 
     /// Return the string table at the given section index.
     ///
+    /// Returns an empty string table if the index is 0.
     /// Returns an error if the section is not a string table.
     #[inline]
     pub fn strings(
@@ -94,6 +95,9 @@ impl<'data, Elf: FileHeader, R: ReadRef<'data>> SectionTable<'data, Elf, R> {
         data: R,
         index: SectionIndex,
     ) -> read::Result<StringTable<'data, R>> {
+        if index == SectionIndex(0) {
+            return Ok(StringTable::default());
+        }
         self.section(index)?
             .strings(endian, data)?
             .read_error("Invalid ELF string section type")