Simplify the futility linker script a bit.

The alignment rules were complicated and not always correct. This change
sorts pointers instead of structures, and aligns the pointer table better.

BUG=chromium:224734
BRANCH=ToT
TEST=make runtests

Change-Id: I16c4e9b777fffe7537127aba15413b54e8e0f0a4
Signed-off-by: Bill Richardson <wfrichar@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/207717
Reviewed-by: Randall Spangler <rspangler@chromium.org>

3 files changed, 32 insertions, 50 deletions

diff --git a/futility/futility.c b/futility/futility.c
index 35620865..52c2d7dd 100644
--- a/futility/futility.c
+++ b/futility/futility.c
@@ -56,17 +56,17 @@ must be located in a directory named \"" SUBDIR "\" underneath\n\
 the " MYNAME " executable.\n\
 \n";
 
-static int help(int argc, char *argv[])
+static int do_help(int argc, char *argv[])
 {
-  futil_cmd_t *cmd;
+  struct futil_cmd_t **cmd;
   int i;
 
   fputs(usage, stdout);
 
   printf("The following commands are built-in:\n");
 
-  for (cmd = futil_cmds_start(); cmd < futil_cmds_end(); cmd++)
-    printf("  %-20s %s\n", cmd->name, cmd->shorthelp);
+  for (cmd = futil_cmds; *cmd; cmd++)
+    printf("  %-20s %s\n", (*cmd)->name, (*cmd)->shorthelp);
   printf("\n");
 
   if (argc) {
@@ -77,7 +77,7 @@ static int help(int argc, char *argv[])
 
   return 0;
 }
-DECLARE_FUTIL_COMMAND(help, help, "show a bit of help");
+DECLARE_FUTIL_COMMAND(help, do_help, "show a bit of help");
 
 
 /******************************************************************************/
@@ -209,7 +209,7 @@ int main(int argc, char *argv[], char *envp[])
   pid_t myproc;
   ssize_t r;
   char *s;
-  futil_cmd_t *cmd;
+  struct futil_cmd_t **cmd;
 
   log_args(argc, argv);
 
@@ -223,7 +223,7 @@ int main(int argc, char *argv[], char *envp[])
   /* Invoked directly by name */
   if (0 == strcmp(progname, MYNAME) || 0 == strcmp(progname, MYNAME_S)) {
     if (argc < 2) {                     /* must have an argument */
-      help(0, 0);
+      do_help(0, 0);
       exit(1);
     }
 
@@ -240,9 +240,9 @@ int main(int argc, char *argv[], char *envp[])
   }
 
   /* See if it's asking for something we know how to do ourselves */
-  for (cmd = futil_cmds_start(); cmd < futil_cmds_end(); cmd++)
-    if (0 == strcmp(cmd->name, progname))
-      return cmd->handler(argc, argv);
+  for (cmd = futil_cmds; *cmd; cmd++)
+    if (0 == strcmp((*cmd)->name, progname))
+      return (*cmd)->handler(argc, argv);
 
   /* Nope, it must be wrapped */
 
diff --git a/futility/futility.h b/futility/futility.h
index c94ce734..005a0ce7 100644
--- a/futility/futility.h
+++ b/futility/futility.h
@@ -8,50 +8,31 @@
 #ifndef VBOOT_REFERENCE_FUTILITY_H_
 #define VBOOT_REFERENCE_FUTILITY_H_
 
-/*
-  Here's a structure to define the commands that futility implements.
- */
-typedef struct {
+/* Here's a structure to define the commands that futility implements. */
+struct futil_cmd_t {
   const char * const name;
   int (*handler)(int argc, char **argv);
   const char * const shorthelp;
-} __attribute__ ((aligned (16))) futil_cmd_t ; /* align for x86_64 ABI */
+};
 
 /*
- * Create an instance in a separate section. We'll have a linker script to
- * gather them all up later, so we can refer to them without explictly
- * declaring every function in a header somewhere
- */
-#define DECLARE_FUTIL_COMMAND(name, handler, shorthelp)          \
-        static const char __futil_cmd_name_##name[] = #name;     \
-        const futil_cmd_t __futil_cmd_##name                     \
-        __attribute__((section(".futil_cmds." #name)))           \
-          = { __futil_cmd_name_##name, handler, shorthelp }
-
-/*
- * Functions to find the command table. We have to play some games here,
- * because the x86_64 ABI says this:
- *
- *   An array uses the same alignment as its elements, except that a local or
- *   global array variable that requires at least 16 bytes, or a C99 local or
- *   global variable-length array variable, always has alignment of at least
- *   16 bytes.
+ * Macro to define a command.
  *
- * The linker script doesn't know what alignment to use for __futil_cmds_start,
- * because that's determined at compile-time and unavailable to the script
- * unless we define one global futil_cmd_t in advance.
+ * This defines the struct, then puts a pointer to it in a separate section.
+ * We'll have a linker script to gather the pointers up later, so we can refer
+ * to them without explictly declaring every function in a header somewhere.
  */
-static inline futil_cmd_t *futil_cmds_start(void)
-{
-  extern uintptr_t __futil_cmds_start[]; /* from linker script */
-  uintptr_t mask = sizeof(futil_cmd_t) - 1;
-  uintptr_t addr = (uintptr_t)(__futil_cmds_start);
-  return (futil_cmd_t *)((addr + mask) & ~mask);
-}
-static inline futil_cmd_t *futil_cmds_end(void)
-{
-  extern uintptr_t __futil_cmds_end[]; /* from linker script */
-  return (futil_cmd_t *)(&__futil_cmds_end[0]);
-}
+#define DECLARE_FUTIL_COMMAND(NAME, HANDLER, SHORTHELP)           \
+        static struct futil_cmd_t cmd_##NAME = {		  \
+                .name = #NAME,                                    \
+                .handler = HANDLER,                               \
+                .shorthelp = SHORTHELP                            \
+        };							  \
+        const struct futil_cmd_t *__cmd_ptr_##NAME		  \
+        __attribute__((section(".futil_cmds." #NAME)))		  \
+          = &cmd_##NAME
+
+/* This is the list of pointers to all commands. */
+extern struct futil_cmd_t *futil_cmds[];
 
 #endif /* VBOOT_REFERENCE_FUTILITY_H_ */
diff --git a/futility/futility.lds b/futility/futility.lds
index e03ab5c4..0650507f 100644
--- a/futility/futility.lds
+++ b/futility/futility.lds
@@ -7,8 +7,9 @@
 SECTIONS
 {
   .rodata : {
-    __futil_cmds_start = .;
+    . = ALIGN(32);
+    futil_cmds = .;                           /* Create the list of commands */
     *(SORT(.futil_cmds.*));
-    __futil_cmds_end = .;
+    QUAD(0);                                  /* Null-terminated */
   }
 }