On May 2, 2012, at 9:12 PM, Steven Bosscher wrote:
> Hello,
>
> alpha-vms is the only target that does not define
> ASM_OUTPUT_ADDR_DIFF_ELT. That makes the code in stmt.c to handle this
> case alpha-vms specific. But there is a better way to handle this:
> Just mimic -fno-jump-tables if flag_pic is nonzero.
>
> Tested by building a cross-compiler for alpha-dec-vms and verifying
> that flag_jump_tables==0 in expand_case.
> OK for trunk?
-fpic is never used on VMS as the 'calling standard' makes it useless: code
is always position independent. In the jump table cases, at worst relocations
entries will be generated by the linker for them.
Tristan.
>
> Ciao!
> Steven
>
>
> * config/alpha/vms.h (SUBTARGET_OVERRIDE_OPTIONS): For pic code,
> unset flag_jump_tables.
> * stmt.c (expand_case): Remove special flag_pic case conditional
> on ASM_OUTPUT_ADDR_DIFF_ELT not being defined.
>
> Index: config/alpha/vms.h
> ===================================================================
> --- config/alpha/vms.h (revision 187046)
> +++ config/alpha/vms.h (working copy)
> @@ -257,7 +257,15 @@ typedef struct {int num_args; enum avms_
> #undef ASM_FINAL_SPEC
>
> /* The VMS convention is to always provide minimal debug info
> - for a traceback unless specifically overridden. */
> + for a traceback unless specifically overridden.
> +
> + Because ASM_OUTPUT_ADDR_DIFF_ELT is not defined for alpha-vms,
> + jump tables cannot be output for PIC code, because you can't put
> + an absolute address in a readonly section. Putting the table in
> + a writable section is a security hole. Therefore, we unset the
> + flag_jump_tables flag, forcing switch statements to be expanded
> + using decision trees. There are probably other ways to address
> + this issue, but using a decision tree is clearly safe. */
>
> #undef SUBTARGET_OVERRIDE_OPTIONS
> #define SUBTARGET_OVERRIDE_OPTIONS \
> @@ -268,6 +276,8 @@ do {
> write_symbols = VMS_DEBUG; \
> debug_info_level = DINFO_LEVEL_TERSE; \
> } \
> + if (flag_pic == 1) \
> + flag_jump_tables = 0; \
> } while (0)
>
> #undef LINK_SPEC
> Index: stmt.c
> ===================================================================
> --- stmt.c (revision 187046)
> +++ stmt.c (working copy)
> @@ -2198,9 +2198,6 @@ expand_case (gimple stmt)
> /* RANGE may be signed, and really large ranges will show up
> as negative numbers. */
> || compare_tree_int (range, 0) < 0
> -#ifndef ASM_OUTPUT_ADDR_DIFF_ELT
> - || flag_pic
> -#endif
> || !flag_jump_tables
> || TREE_CONSTANT (index_expr)
> /* If neither casesi or tablejump is available, we can
