Program mutable lamports (#4964)

programs/bpf/rust/external_spend/.gitignore

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+/target/
+
+Cargo.lock

programs/bpf/rust/external_spend/Cargo.toml

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+
+# Note: This crate must be built using build.sh
+
+[package]
+name = "solana-bpf-rust-external-spend"
+version = "0.17.0"
+description = "Solana BPF external spend program written in Rust"
+authors = ["Solana Maintainers <maintainers@solana.com>"]
+repository = "https://github.com/solana-labs/solana"
+license = "Apache-2.0"
+homepage = "https://solana.com/"
+edition = "2018"
+
+[dependencies]
+solana-sdk-bpf-utils = { path = "../../../../sdk/bpf/rust/rust-utils", version = "0.17.0" }
+
+[workspace]
+members = []
+
+[lib]
+crate-type = ["cdylib"]
+name = "solana_bpf_rust_external_spend"

programs/bpf/rust/external_spend/Xargo.toml

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+[dependencies.compiler_builtins]
+path = "../../../../sdk/bpf/dependencies/rust-bpf-sysroot/src/compiler-builtins"
+features = ["c", "mem"]
+
+[target.bpfel-unknown-unknown.dependencies]
+alloc = { path = "../../../../sdk/bpf/dependencies/rust-bpf-sysroot/src/liballoc" }

programs/bpf/rust/external_spend/src/lib.rs

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+//! @brief Example Rust-based BPF program that moves a lamport from one account to another
+
+#![no_std]
+#![allow(unreachable_code)]
+#![allow(unused_attributes)]
+
+extern crate solana_sdk_bpf_utils;
+
+use solana_sdk_bpf_utils::entrypoint::*;
+use solana_sdk_bpf_utils::{entrypoint, info};
+
+entrypoint!(process_instruction);
+fn process_instruction(ka: &mut [SolKeyedAccount], _info: &SolClusterInfo, _data: &[u8]) -> bool {
+    // account 0 is the mint and not owned by this program, any debit of its lamports
+    // should result in a failed program execution.  Test to ensure that this debit
+    // is seen by the runtime and fails as expected
+    *ka[0].lamports -= 1;
+
+    info!("Success");
+    true
+}