Refuse to load non-EXEC/non-RISC-V/non-V1 ELFs (#388)

Stricter validation of ELF binaries improves usability with informative
assertions. This prevents users from loading ELF relocatable files and
binaries compiled for their (non-RISC-V) workstations, for example.

Without this patch, spike would attempt to load nearly any ELF given,
but it would usually fail with an error about debug module accesses,
since the given ELF causes accesses in the debug module's memory space.
Even if spike successfully loaded the ELF file, it would still misbehave
during simulation, for example in the case of ELF relocatable files.

ELF magic numbers come from official ELF documents:
TIS ELF spec v1.2, via Linux Foundation Referenced Specifications
See: https://refspecs.linuxbase.org/

RISC-V magic number comes from official RISC-V ELF documents:
See: riscv/riscv-elf-psabi-doc@60c25981b62c0b43d16142f8a12c8b1e98e60d4d

1 files changed, 3 insertions, 0 deletions

diff --git a/fesvr/elfloader.cc b/fesvr/elfloader.cc
index 610e520..fe0fbf0 100644
--- a/fesvr/elfloader.cc
+++ b/fesvr/elfloader.cc
@@ -32,6 +32,9 @@ std::map<std::string, uint64_t> load_elf(const char* fn, memif_t* memif, reg_t*
   const Elf64_Ehdr* eh64 = (const Elf64_Ehdr*)buf;
   assert(IS_ELF32(*eh64) || IS_ELF64(*eh64));
   assert(IS_ELFLE(*eh64));
+  assert(IS_ELF_EXEC(*eh64));
+  assert(IS_ELF_RISCV(*eh64));
+  assert(IS_ELF_VCURRENT(*eh64));
 
   std::vector<uint8_t> zeros;
   std::map<std::string, uint64_t> symbols;