[PULL 12/18] linux-user: detect mismatched ELF ABI in qemu-mips[n32][el]

[Laurent Vivier]

From: Carlo Marcelo Arenas Belón <carenas@gmail.com>

MIPS provides 2 ILP32 ABIs, and therefore 4 possible qemu-mips binaries
with 2 pairs using the same endianess and bitness.

This could lead to an O32 image loading in the N32 binary or vice versa
and in cryptic errors (if lucky that the CPU doesn't match the FPU used)
like :

  qemu: Unexpected FPU mode       (o32 ELF loaded to qemu-mipsn32[el])
  ELF binary's NaN mode not supported by CPU    (n32 -> qemu-mips[el])

Add an ABI check macro that could be used while checking the ELF header
that relies in the ABI2 flag to identify n32 binaries and abort instead
early with a more descriptive error :

  Invalid ELF image for this architecture

Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20200823101703.18451-1-carenas@gmail.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
---
 linux-user/elfload.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index fe9dfe795ddd..69936dcd4595 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -918,6 +918,12 @@ static void elf_core_copy_regs(target_elf_gregset_t *regs, 
const CPUPPCState *en
 
 #define elf_check_arch(x) ((x) == EM_MIPS || (x) == EM_NANOMIPS)
 
+#ifdef TARGET_ABI_MIPSN32
+#define elf_check_abi(x) ((x) & EF_MIPS_ABI2)
+#else
+#define elf_check_abi(x) (!((x) & EF_MIPS_ABI2))
+#endif
+
 static inline void init_thread(struct target_pt_regs *regs,
                                struct image_info *infop)
 {
@@ -1487,6 +1493,10 @@ static void elf_core_copy_regs(target_elf_gregset_t 
*regs,
 #define elf_check_arch(x) ((x) == ELF_ARCH)
 #endif
 
+#ifndef elf_check_abi
+#define elf_check_abi(x) (1)
+#endif
+
 #ifndef ELF_HWCAP
 #define ELF_HWCAP 0
 #endif
@@ -1644,6 +1654,7 @@ static bool elf_check_ident(struct elfhdr *ehdr)
 static bool elf_check_ehdr(struct elfhdr *ehdr)
 {
     return (elf_check_arch(ehdr->e_machine)
+            && elf_check_abi(ehdr->e_flags)
             && ehdr->e_ehsize == sizeof(struct elfhdr)
             && ehdr->e_phentsize == sizeof(struct elf_phdr)
             && (ehdr->e_type == ET_EXEC || ehdr->e_type == ET_DYN));
-- 
2.26.2