[PATCH 1/8] MIPS: Use a union to access the ELF file header

[Maciej W. Rozycki]

Rewrite `arch_elf_pt_proc' and `arch_check_elf' using a union to access 
the ELF file header.

Signed-off-by: Maciej W. Rozycki <ma...@imgtec.com>
---
linux-mips-elf-ehdr.diff
Index: linux-sfr-test/arch/mips/kernel/elf.c
===================================================================
--- linux-sfr-test.orig/arch/mips/kernel/elf.c  2015-09-04 22:46:08.374274000 
+0100
+++ linux-sfr-test/arch/mips/kernel/elf.c       2015-09-04 22:47:56.448146000 
+0100
@@ -68,15 +68,23 @@ static struct mode_req none_req = { true
 int arch_elf_pt_proc(void *_ehdr, void *_phdr, struct file *elf,
                     bool is_interp, struct arch_elf_state *state)
 {
-       struct elf32_hdr *ehdr32 = _ehdr;
+       union {
+               struct elf32_hdr e32;
+               struct elf64_hdr e64;
+       } *ehdr = _ehdr;
        struct elf32_phdr *phdr32 = _phdr;
        struct elf64_phdr *phdr64 = _phdr;
        struct mips_elf_abiflags_v0 abiflags;
+       bool elf32;
+       u32 flags;
        int ret;
 
+       elf32 = ehdr->e32.e_ident[EI_CLASS] == ELFCLASS32;
+       flags = elf32 ? ehdr->e32.e_flags : ehdr->e64.e_flags;
+
        /* Lets see if this is an O32 ELF */
-       if (ehdr32->e_ident[EI_CLASS] == ELFCLASS32) {
-               if (ehdr32->e_flags & EF_MIPS_FP64) {
+       if (elf32) {
+               if (flags & EF_MIPS_FP64) {
                        /*
                         * Set MIPS_ABI_FP_OLD_64 for EF_MIPS_FP64. We will 
override it
                         * later if needed
@@ -123,10 +131,17 @@ int arch_elf_pt_proc(void *_ehdr, void *
 int arch_check_elf(void *_ehdr, bool has_interpreter,
                   struct arch_elf_state *state)
 {
-       struct elf32_hdr *ehdr = _ehdr;
+       union {
+               struct elf32_hdr e32;
+               struct elf64_hdr e64;
+       } *ehdr = _ehdr;
        struct mode_req prog_req, interp_req;
        int fp_abi, interp_fp_abi, abi0, abi1, max_abi;
-       bool is_mips64;
+       bool elf32;
+       u32 flags;
+
+       elf32 = ehdr->e32.e_ident[EI_CLASS] == ELFCLASS32;
+       flags = elf32 ? ehdr->e32.e_flags : ehdr->e64.e_flags;
 
        if (!config_enabled(CONFIG_MIPS_O32_FP64_SUPPORT))
                return 0;
@@ -142,21 +157,18 @@ int arch_check_elf(void *_ehdr, bool has
                abi0 = abi1 = fp_abi;
        }
 
-       is_mips64 = (ehdr->e_ident[EI_CLASS] == ELFCLASS64) ||
-                   (ehdr->e_flags & EF_MIPS_ABI2);
+       if (elf32 && !(flags & EF_MIPS_ABI2)) {
+               /* Default to a mode capable of running code expecting FR=0 */
+               state->overall_fp_mode = cpu_has_mips_r6 ? FP_FRE : FP_FR0;
 
-       if (is_mips64) {
+               /* Allow all ABIs we know about */
+               max_abi = MIPS_ABI_FP_64A;
+       } else {
                /* MIPS64 code always uses FR=1, thus the default is easy */
                state->overall_fp_mode = FP_FR1;
 
                /* Disallow access to the various FPXX & FP64 ABIs */
                max_abi = MIPS_ABI_FP_SOFT;
-       } else {
-               /* Default to a mode capable of running code expecting FR=0 */
-               state->overall_fp_mode = cpu_has_mips_r6 ? FP_FRE : FP_FR0;
-
-               /* Allow all ABIs we know about */
-               max_abi = MIPS_ABI_FP_64A;
        }
 
        if ((abi0 > max_abi && abi0 != MIPS_ABI_FP_UNKNOWN) ||
--
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