From b4cabde4a4fec129378988987e14b7148c074c04 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?kleines=20Filmr=C3=B6llchen?= <filmroellchen@serenityos.org>
Date: Fri, 13 Oct 2023 20:10:33 +0200
Subject: [PATCH] LibELF: Add initial RISC-V support

This is an almost-minimal patchset to get RISC-V ELF files to pass
validation. Unlike other architectures, eflags are actually used here.
---
 Userland/Libraries/LibELF/ELFABI.h       | 12 ++++++++++++
 Userland/Libraries/LibELF/Validation.cpp | 22 +++++++++++++++++-----
 2 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/Userland/Libraries/LibELF/ELFABI.h b/Userland/Libraries/LibELF/ELFABI.h
index 1f54afe89f..2372d6587e 100644
--- a/Userland/Libraries/LibELF/ELFABI.h
+++ b/Userland/Libraries/LibELF/ELFABI.h
@@ -204,6 +204,7 @@ typedef struct {
 #define EM_X86_64 EM_AMD64
 #define EM_VAX 75      /* DEC VAX */
 #define EM_AARCH64 183 /* ARM 64-bit architecture (AArch64) */
+#define EM_RISCV 243   /* RISC-V */
 
 /* Non-standard */
 #define EM_ALPHA_EXP 0x9026 /* DEC ALPHA */
@@ -219,6 +220,17 @@ typedef struct {
 /* Magic for e_phnum: get real value from sh_info of first section header */
 #define PN_XNUM 0xffff
 
+/* RISC-V specific e_flags */
+/* See: RISC-V ABI Specification 1.0, Section 8.1: File Header */
+#define EF_RISCV_RVC 0x0001              /* Binary targets the Compressed ABI */
+#define EF_RISCV_FLOAT_ABI_SOFT 0x0000   /* No hardware float ABI in use */
+#define EF_RISCV_FLOAT_ABI_SINGLE 0x0002 /* 32-bit hardware float ABI */
+#define EF_RISCV_FLOAT_ABI_DOUBLE 0x0004 /* 64-bit hardware float ABI */
+#define EF_RISCV_FLOAT_ABI_QUAD 0x0006   /* 128-bit hardware float ABI */
+#define EF_RISCV_FLOAT_ABI 0x0006        /* Test mask for float ABIs */
+#define EF_RISCV_RVE 0x0008              /* Binary targets the Embedded ABI */
+#define EF_RISCV_TSO 0x0010              /* Binary requires Ztso extension */
+
 /* Section Header */
 typedef struct {
     Elf32_Word sh_name;      /* name - index into section header
diff --git a/Userland/Libraries/LibELF/Validation.cpp b/Userland/Libraries/LibELF/Validation.cpp
index 2d898678c6..8ccb39b3dc 100644
--- a/Userland/Libraries/LibELF/Validation.cpp
+++ b/Userland/Libraries/LibELF/Validation.cpp
@@ -59,8 +59,8 @@ bool validate_elf_header(ElfW(Ehdr) const& elf_header, size_t file_size, bool ve
         return false;
     }
 
-    auto expected_machines = Array { EM_X86_64, EM_AARCH64 };
-    auto expected_machine_names = Array { "x86-64"sv, "aarch64"sv };
+    auto expected_machines = Array { EM_X86_64, EM_AARCH64, EM_RISCV };
+    auto expected_machine_names = Array { "x86-64"sv, "aarch64"sv, "riscv64"sv };
 
     if (!expected_machines.span().contains_slow(elf_header.e_machine)) {
         if (verbose)
@@ -117,9 +117,21 @@ bool validate_elf_header(ElfW(Ehdr) const& elf_header, size_t file_size, bool ve
     }
 
     if (0 != elf_header.e_flags) {
-        if (verbose)
-            dbgln("File has incorrect ELF header flags...? ({}), expected ({}).", elf_header.e_flags, 0);
-        return false;
+        // TODO: Refuse to run C ABI binaries on system without the C extension.
+        // TODO: Refuse to run TSO ABI binaries on system without the Ztso extension.
+        if (elf_header.e_machine == EM_RISCV) {
+            auto float_abi = elf_header.e_flags & EF_RISCV_FLOAT_ABI;
+            // TODO: Support 32-bit hardware float ABI somehow?
+            if (float_abi != EF_RISCV_FLOAT_ABI_DOUBLE) {
+                if (verbose)
+                    dbgln("File has unsupported float ABI ({}), only double ({}) is supported.", float_abi, EF_RISCV_FLOAT_ABI_DOUBLE);
+                return false;
+            }
+        } else {
+            if (verbose)
+                dbgln("File has incorrect ELF header flags...? ({}), expected ({}).", elf_header.e_flags, 0);
+            return false;
+        }
     }
 
     if (0 != elf_header.e_phnum && sizeof(ElfW(Phdr)) != elf_header.e_phentsize) {