risc0-binfmt: use no_std for anyhow and elf (#869)

This change uses `default-features = false` for `anyhow` and `elf`
crates. Using these features resulted in several compiler warnings about
error type conversions. To fix the errors, I've added pattern matching
for Ok(...) and Err(...) mainly for u64 -> u32 conversions.

---------

Co-authored-by: Frank Laub <flaub@risc0.com>
Co-authored-by: Victor Graf <victor@risczero.com>

risc0/binfmt/Cargo.toml

@@ -15,13 +15,13 @@ tracing = "0.1"
 tracing-subscriber = "0.3"
 
 [dependencies]
-anyhow = { version = "1.0" }
-elf = "0.7"
+anyhow = { version = "1.0", default-features = false }
+elf = { version = "0.7", default-features = false }
 log = "0.4"
 risc0-zkp = { workspace = true }
 risc0-zkvm-platform = { workspace = true }
-serde = { version = "1.0", default-features = false, features = ["derive"] }
+serde = { version = "1.0", default-features = false, features = ["derive", "alloc"] }
 
 [features]
 default = ["std"]
-std = ["log/std", "risc0-zkp/std", "serde/std"]
+std = ["anyhow/std", "elf/std", "log/std", "risc0-zkp/std", "serde/std"]

risc0/binfmt/src/elf.rs

@@ -32,7 +32,8 @@ impl Program {
     /// Initialize a RISC Zero Program from an appropriate ELF file
     pub fn load_elf(input: &[u8], max_mem: u32) -> Result<Program> {
         let mut image: BTreeMap<u32, u32> = BTreeMap::new();
-        let elf = ElfBytes::<LittleEndian>::minimal_parse(input)?;
+        let elf = ElfBytes::<LittleEndian>::minimal_parse(input)
+            .map_err(|err| anyhow!("Elf parse error: {err}"))?;
         if elf.ehdr.class != Class::ELF32 {
             bail!("Not a 32-bit ELF");
         }
@@ -42,7 +43,11 @@ impl Program {
         if elf.ehdr.e_type != elf::abi::ET_EXEC {
             bail!("Invalid ELF type, must be executable");
         }
-        let entry: u32 = elf.ehdr.e_entry.try_into()?;
+        let entry: u32 = elf
+            .ehdr
+            .e_entry
+            .try_into()
+            .map_err(|err| anyhow!("e_entry was larger than 32 bits. {err}"))?;
         if entry >= max_mem || entry % 4 != 0 {
             bail!("Invalid entrypoint");
         }
@@ -51,16 +56,28 @@ impl Program {
             bail!("Too many program headers");
         }
         for segment in segments.iter().filter(|x| x.p_type == elf::abi::PT_LOAD) {
-            let file_size: u32 = segment.p_filesz.try_into()?;
+            let file_size: u32 = segment
+                .p_filesz
+                .try_into()
+                .map_err(|err| anyhow!("filesize was larger than 32 bits. {err}"))?;
             if file_size >= max_mem {
                 bail!("Invalid segment file_size");
             }
-            let mem_size: u32 = segment.p_memsz.try_into()?;
+            let mem_size: u32 = segment
+                .p_memsz
+                .try_into()
+                .map_err(|err| anyhow!("mem_size was larger than 32 bits {err}"))?;
             if mem_size >= max_mem {
                 bail!("Invalid segment mem_size");
             }
-            let vaddr: u32 = segment.p_vaddr.try_into()?;
-            let offset: u32 = segment.p_offset.try_into()?;
+            let vaddr: u32 = segment
+                .p_vaddr
+                .try_into()
+                .map_err(|err| anyhow!("vaddr is larger than 32 bits. {err}"))?;
+            let offset: u32 = segment
+                .p_offset
+                .try_into()
+                .map_err(|err| anyhow!("offset is larger than 32 bits. {err}"))?;
             for i in (0..mem_size).step_by(4) {
                 let addr = vaddr.checked_add(i).context("Invalid segment vaddr")?;
                 if i >= file_size {

risc0/cargo-risczero/src/commands/build_guest.rs

@@ -213,11 +213,11 @@ mod test {
         let tester = Tester::new("risc0/zkvm/methods/guest/Cargo.toml");
         tester.compare_image_id(
             "risc0_zkvm_methods_guest/multi_test",
-            "e292842cb47a065057c3b7dae52c93dd849307e2e2746eec22c58517a3474f92",
+            "417778745b43c82a20db33a55c2b1d6e0805e0fa7eec80c9654e7321121e97af",
         );
         tester.compare_image_id(
             "risc0_zkvm_methods_guest/hello_commit",
-            "993d3ceaefdbcd0dc855418c16a60ada197954d15cb9e7568ca5a70772abc501",
+            "c7c399c25ecf26b79e987ed060efce1f0836a594ad1059b138b6ed2f123dad38",
         );
         tester.compare_image_id(
             "risc0_zkvm_methods_guest/slice_io",