From 6a1aff20685fecafe88760345f1cac9141ac2af3 Mon Sep 17 00:00:00 2001
From: dramforever <dramforever@live.com>
Date: Sun, 19 Mar 2023 14:23:27 +0800
Subject: [PATCH] Rework riscv -march and -mabi detection

Instead of adding cases for all the operating systems, Use target
architecture directly as ISA string, replacing "riscv" with "rv", and
detect floating point ABI based on support for the D and F extensions.

Fixes #795
---
 src/lib.rs | 47 ++++++++++++++++++++++++++++++-----------------
 1 file changed, 30 insertions(+), 17 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index 688f476fe..906bf68e3 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1958,25 +1958,38 @@ impl Build {
                     let mut parts = target.split('-');
                     if let Some(arch) = parts.next() {
                         let arch = &arch[5..];
-                        if target.contains("linux") && arch.starts_with("64") {
-                            cmd.args.push(("-march=rv64gc").into());
-                            cmd.args.push("-mabi=lp64d".into());
-                        } else if target.contains("freebsd") && arch.starts_with("64") {
-                            cmd.args.push(("-march=rv64gc").into());
-                            cmd.args.push("-mabi=lp64d".into());
-                        } else if target.contains("openbsd") && arch.starts_with("64") {
-                            cmd.args.push(("-march=rv64gc").into());
-                            cmd.args.push("-mabi=lp64d".into());
-                        } else if target.contains("linux") && arch.starts_with("32") {
-                            cmd.args.push(("-march=rv32gc").into());
-                            cmd.args.push("-mabi=ilp32d".into());
-                        } else if arch.starts_with("64") {
-                            cmd.args.push(("-march=rv".to_owned() + arch).into());
-                            cmd.args.push("-mabi=lp64".into());
+
+                        // Assume that "rv{arch}" is a valid RISC-V ISA string.
+                        // The compiler would error out otherwise, and we fix
+                        // that later.
+                        cmd.args.push(("-march=rv".to_owned() + arch).into());
+
+                        // Detect single-letter extensions from `arch`, assuming
+                        // no version numbers and canonical order
+                        let riscv_implements = |ext: &str| -> bool {
+                            let pattern = |c| ['_', 'z', 's'].contains(&c);
+                            let single_letter =
+                                arch.split(pattern).next().expect("Empty arch string?");
+                            single_letter.contains(ext)
+                        };
+
+                        let float_abi = if riscv_implements("g") || riscv_implements("d") {
+                            // Implements "d" (double-float), use double-float ABI
+                            "d"
+                        } else if riscv_implements("f") {
+                            // Implements "f" (single-float), use single-float ABI
+                            "f"
+                        } else {
+                            // No floating support, use soft-float ABI
+                            ""
+                        };
+
+                        if arch.starts_with("64") {
+                            cmd.args.push(("-mabi=lp64".to_owned() + float_abi).into());
                         } else {
-                            cmd.args.push(("-march=rv".to_owned() + arch).into());
-                            cmd.args.push("-mabi=ilp32".into());
+                            cmd.args.push(("-mabi=ilp32".to_owned() + float_abi).into());
                         }
+
                         cmd.args.push("-mcmodel=medany".into());
                     }
                 }