linux-user: introduce functions to detect CPU type

Add a function to return ELF e_flags and use it
to select the CPU model.
Signed-off-by: NYunQiang Su <syq@debian.org>
[lv: split the patch and some cleanup in get_elf_eflags()]
Signed-off-by: NLaurent Vivier <laurent@vivier.eu>
Reviewed-by: NRichard Henderson <richard.henderson@linaro.org>
Message-Id: <20180220173307.25125-3-laurent@vivier.eu>

linux-user/elfload.c

@@ -2396,6 +2396,41 @@ give_up:
     g_free(syms);
 }
 
+uint32_t get_elf_eflags(int fd)
+{
+    struct elfhdr ehdr;
+    off_t offset;
+    int ret;
+
+    /* Read ELF header */
+    offset = lseek(fd, 0, SEEK_SET);
+    if (offset == (off_t) -1) {
+        return 0;
+    }
+    ret = read(fd, &ehdr, sizeof(ehdr));
+    if (ret < sizeof(ehdr)) {
+        return 0;
+    }
+    offset = lseek(fd, offset, SEEK_SET);
+    if (offset == (off_t) -1) {
+        return 0;
+    }
+
+    /* Check ELF signature */
+    if (!elf_check_ident(&ehdr)) {
+        return 0;
+    }
+
+    /* check header */
+    bswap_ehdr(&ehdr);
+    if (!elf_check_ehdr(&ehdr)) {
+        return 0;
+    }
+
+    /* return architecture id */
+    return ehdr.e_flags;
+}
+
 int load_elf_binary(struct linux_binprm *bprm, struct image_info *info)
 {
     struct image_info interp_info;

linux-user/main.c

@@ -4344,8 +4344,17 @@ int main(int argc, char **argv, char **envp)
 
     init_qemu_uname_release();
 
+    execfd = qemu_getauxval(AT_EXECFD);
+    if (execfd == 0) {
+        execfd = open(filename, O_RDONLY);
+        if (execfd < 0) {
+            printf("Error while loading %s: %s\n", filename, strerror(errno));
+            _exit(EXIT_FAILURE);
+        }
+    }
+
     if (cpu_model == NULL) {
-        cpu_model = cpu_get_model(0);
+        cpu_model = cpu_get_model(get_elf_eflags(execfd));
     }
     tcg_exec_init(0);
     /* NOTE: we need to init the CPU at this stage to get
@@ -4438,15 +4447,6 @@ int main(int argc, char **argv, char **envp)
     cpu->opaque = ts;
     task_settid(ts);
 
-    execfd = qemu_getauxval(AT_EXECFD);
-    if (execfd == 0) {
-        execfd = open(filename, O_RDONLY);
-        if (execfd < 0) {
-            printf("Error while loading %s: %s\n", filename, strerror(errno));
-            _exit(EXIT_FAILURE);
-        }
-    }
-
     ret = loader_exec(execfd, filename, target_argv, target_environ, regs,
         info, &bprm);
     if (ret != 0) {

linux-user/qemu.h

@@ -186,6 +186,7 @@ int loader_exec(int fdexec, const char *filename, char **argv, char **envp,
              struct target_pt_regs * regs, struct image_info *infop,
              struct linux_binprm *);
 
+uint32_t get_elf_eflags(int fd);
 int load_elf_binary(struct linux_binprm *bprm, struct image_info *info);
 int load_flt_binary(struct linux_binprm *bprm, struct image_info *info);