read/pe: `dynamic_symbols` iterator is empty

[afonso360]

👋 Hey,

When reading Windows DLL's the dynamic_symbols() API returns an empty iterator. I tried running the objdump example and it correctly detects the symbols as Exports.

It also looks like its somewhat intentional?

object/src/read/pe/file.rs

Lines 244 to 247 in 40d77b2

	CoffSymbolIterator {
	file: &self.common,
	// Hack: don't return any.
	index: self.common.symbols.len(),

So I'm not sure if we should be using some other API?

[bjorn3]

So I'm not sure if we should be using some other API?

symbols() contains unexported symbols and doesn't work for stripped dynamic libraries.

[philipc]

dynamic_symbols is primarily for ELF which often has two symbol tables, but PE doesn't have this so we leave it empty. To write code which works for both PE and ELF, probably what you want is to use symbols first, and fall back to dynamic_symbols if symbols is empty (or you could chain the two together).

[bjorn3]

Looking at dynamic_symbols first is more correct I think if you want to emulate a dynamic linker (like in this case). Also can't PE have dynamic_symbols return the same value as symbols given that there is no distinction between the two at file format level for PE executables?

[bjorn3]

By the way in my usecase (cg_clif's jit mode) it important that no symbols are returned for which dlsym or the equivalent on windows fails as what it does is dlsym all symbols to add to the symbol mapping of Cranelift's jit engine.

[afonso360]

For this DLL I think neither symbols or dynamic_symbols are producing anything (if I'm reading this right):

`cargo run --bin objdump \\?\C:\Users\Afonso\CLionProjects\rustc_codegen_cranelift\target\out\mini_core.dll`

PS C:\Users\Afonso\CLionProjects\object\crates\examples> cargo run --bin objdump \\?\C:\Users\Afonso\CLionProjects\rustc_codegen_cranelift\target\out\mini_core.dll
    Finished dev [unoptimized + debuginfo] target(s) in 0.05s
     Running `C:\Users\Afonso\CLionProjects\object\target\debug\objdump.exe \\?\C:\Users\Afonso\CLionProjects\rustc_codegen_cranelift\target\out\mini_core.dll`
Format: Pe Little-endian 64-bit
Kind: Dynamic
Architecture: X86_64
Flags: Coff { characteristics: 2022 }
Relative Address Base: 180000000
Entry Address: 180001be0
PDB file: C:\Users\Afonso\CLionProjects\rustc_codegen_cranelift\target\out\mini_core.pdb, GUID: [c3, e2, c0, 9f, bf, 2c, 9d, 42, bd, 14, a7, b4, fa, 60, 5d, 29], Age: 1
Segment { name: ".text", address: 180001000, size: 1548 }
Segment { name: ".rdata", address: 180003000, size: 236e }
Segment { name: ".data", address: 180006000, size: d8 }
Segment { name: ".pdata", address: 180007000, size: 198 }
Segment { name: ".rustc", address: 180008000, size: be32 }
Segment { name: ".reloc", address: 180014000, size: 7c }
1: Section { name: ".text", address: 180001000, size: 1548, align: 1000, kind: Text, flags: Coff { characteristics: 60000020 } }
2: Section { name: ".rdata", address: 180003000, size: 236e, align: 1000, kind: ReadOnlyData, flags: Coff { characteristics: 40000040 } }
3: Section { name: ".data", address: 180006000, size: d8, align: 1000, kind: Data, flags: Coff { characteristics: c0000040 } }
4: Section { name: ".pdata", address: 180007000, size: 198, align: 1000, kind: ReadOnlyData, flags: Coff { characteristics: 40000040 } }
5: Section { name: ".rustc", address: 180008000, size: be32, align: 1000, kind: ReadOnlyData, flags: Coff { characteristics: 40000040 } }
6: Section { name: ".reloc", address: 180014000, size: 7c, align: 1000, kind: Other, flags: Coff { characteristics: 42000040 } }

Symbols

Dynamic symbols

Import { library: "KERNEL32.dll", name: "QueryPerformanceCounter" }
Import { library: "KERNEL32.dll", name: "GetCurrentProcessId" }
Import { library: "KERNEL32.dll", name: "GetCurrentThreadId" }
Import { library: "KERNEL32.dll", name: "GetSystemTimeAsFileTime" }
Import { library: "KERNEL32.dll", name: "DisableThreadLibraryCalls" }
Import { library: "KERNEL32.dll", name: "InitializeSListHead" }
Import { library: "KERNEL32.dll", name: "RtlCaptureContext" }
Import { library: "KERNEL32.dll", name: "RtlLookupFunctionEntry" }
Import { library: "KERNEL32.dll", name: "RtlVirtualUnwind" }
Import { library: "KERNEL32.dll", name: "IsDebuggerPresent" }
Import { library: "KERNEL32.dll", name: "UnhandledExceptionFilter" }
Import { library: "KERNEL32.dll", name: "SetUnhandledExceptionFilter" }
Import { library: "KERNEL32.dll", name: "IsProcessorFeaturePresent" }
Import { library: "VCRUNTIME140.dll", name: "__C_specific_handler" }
Import { library: "VCRUNTIME140.dll", name: "__std_type_info_destroy_list" }
Import { library: "VCRUNTIME140.dll", name: "memset" }
Import { library: "api-ms-win-crt-stdio-l1-1-0.dll", name: "__stdio_common_vfprintf" }
Import { library: "api-ms-win-crt-stdio-l1-1-0.dll", name: "__acrt_iob_func" }
Import { library: "api-ms-win-crt-stdio-l1-1-0.dll", name: "puts" }
Import { library: "api-ms-win-crt-heap-l1-1-0.dll", name: "malloc" }
Import { library: "api-ms-win-crt-runtime-l1-1-0.dll", name: "_cexit" }
Import { library: "api-ms-win-crt-runtime-l1-1-0.dll", name: "_execute_onexit_table" }
Import { library: "api-ms-win-crt-runtime-l1-1-0.dll", name: "_initterm" }
Import { library: "api-ms-win-crt-runtime-l1-1-0.dll", name: "_initialize_onexit_table" }
Import { library: "api-ms-win-crt-runtime-l1-1-0.dll", name: "_initialize_narrow_environment" }
Import { library: "api-ms-win-crt-runtime-l1-1-0.dll", name: "_configure_narrow_argv" }
Import { library: "api-ms-win-crt-runtime-l1-1-0.dll", name: "_seh_filter_dll" }
Import { library: "api-ms-win-crt-runtime-l1-1-0.dll", name: "_initterm_e" }

Export { name: "_ZN37_$LT$i8$u20$as$u20$mini_core..Add$GT$3add17hb127499ffca5eb39E", address: 180001102 }
Export { name: "_ZN37_$LT$i8$u20$as$u20$mini_core..Neg$GT$3neg17hb5f9c32b4322992bE", address: 1800016a8 }
Export { name: "_ZN37_$LT$i8$u20$as$u20$mini_core..Sub$GT$3sub17hc6b45c8b1fdf4baeE", address: 180001214 }
Export { name: "_ZN37_$LT$u8$u20$as$u20$mini_core..Add$GT$3add17h6aec7f1f2aef0c61E", address: 1800010c1 }
Export { name: "_ZN37_$LT$u8$u20$as$u20$mini_core..Mul$GT$3mul17h6e7be35e79f50831E", address: 180001013 }
Export { name: "_ZN37_$LT$u8$u20$as$u20$mini_core..Sub$GT$3sub17h4383d5a72c63d48cE", address: 1800011d3 }
Export { name: "_ZN38_$LT$f32$u20$as$u20$mini_core..Neg$GT$3neg17hf7deaec39c75b9b3E", address: 180001767 }
Export { name: "_ZN38_$LT$i16$u20$as$u20$mini_core..Neg$GT$3neg17he1c97940a064a5beE", address: 1800016fb }
Export { name: "_ZN38_$LT$i16$u20$as$u20$mini_core..Sub$GT$3sub17h376d768bdbfcdd26E", address: 18000125f }
Export { name: "_ZN39_$LT$bool$u20$as$u20$mini_core..Not$GT$3not17h6bc448b7065a9a2fE", address: 180001000 }
Export { name: "_ZN39_$LT$u128$u20$as$u20$mini_core..Shl$GT$3shl17h088219955c05482aE", address: 1800015ca }
Export { name: "_ZN40_$LT$isize$u20$as$u20$mini_core..Neg$GT$3neg17hcac1e45aa1338a0fE", address: 180001707 }
Export { name: "_ZN40_$LT$usize$u20$as$u20$mini_core..Add$GT$3add17h35d64e8497e37cacE", address: 18000114d }
Export { name: "_ZN40_$LT$usize$u20$as$u20$mini_core..Mul$GT$3mul17hfed9f86051e68be4E", address: 18000105b }
Export { name: "_ZN40_$LT$usize$u20$as$u20$mini_core..Rem$GT$3rem17h7d7f89ad5d5ed33aE", address: 1800012ac }
Export { name: "_ZN40_$LT$usize$u20$as$u20$mini_core..Sub$GT$3sub17h51ec339336055bd2E", address: 180001190 }
Export { name: "_ZN45_$LT$char$u20$as$u20$mini_core..PartialEq$GT$2ne17hfd5706d3b12f20a3E", address: 1800015b4 }
Export { name: "_ZN45_$LT$u128$u20$as$u20$mini_core..PartialEq$GT$2eq17h0ffeaf1e4f7b3adeE", address: 180001444 }
Export { name: "_ZN45_$LT$u128$u20$as$u20$mini_core..PartialEq$GT$2ne17h8802883f7869eb63E", address: 18000147a }
Export { name: "_ZN46_$LT$isize$u20$as$u20$mini_core..PartialEq$GT$2eq17hdfc1d4ff93090061E", address: 180001572 }
Export { name: "_ZN46_$LT$isize$u20$as$u20$mini_core..PartialEq$GT$2ne17h07d0888bcbdc6c04E", address: 180001588 }
Export { name: "_ZN46_$LT$usize$u20$as$u20$mini_core..PartialEq$GT$2eq17h4bf1c72c5c1f558fE", address: 1800014b0 }
Export { name: "_ZN46_$LT$usize$u20$as$u20$mini_core..PartialEq$GT$2ne17h4936b5511acd9acfE", address: 1800014c6 }
Export { name: "_ZN57_$LT$$RF$bool$u20$as$u20$mini_core..BitOr$LT$bool$GT$$GT$5bitor17hed6ff0fa4aefd001E", address: 180001309 }
Export { name: "_ZN9mini_core18panic_bounds_check17hf264484ec56e4a33E", address: 1800017da }
Export { name: "_ZN9mini_core5panic17h555d4b90a53c9ec6E", address: 18000179c }
Export { name: "_ZN9mini_core8A_STATIC17hc53ef79cc689fdd5E", address: 1800035d7 }
Export { name: "_ZN9mini_core8allocate17h0a37b8e5fe56d584E", address: 180001828 }
Export { name: "rust_eh_personality", address: 18000181f }
Export { name: "rust_metadata_mini_core_4f527cb27cbd947d", address: 180008000 }

I'm not sure if this is an issue in object or elsewhere, I'm not too familiar with any of this.

[philipc]

Looking at dynamic_symbols first is more correct I think if you want to emulate a dynamic linker (like in this case).

The dynamic linker doesn't use the symbol table for PE. Probably what you want is imports or exports instead then.

[afonso360]

It sounds like this isn't very actionable on your side, thanks for all the help, and sorry for the noise!