Re: [PATCH] ld: harmonize the value of --enable-warn-execstack=no option

[Alan Modra <amodra@gmail.com>]

On Tue, May 17, 2022 at 02:51:40PM +0200, Clément Chigot via Binutils wrote:
> This patch sets the configure value of warn-execstack to 2 when
> disabled as expected by bfd.
> 
> ld/ChangeLog:
> 
>         * configure.ac: Update ac_default_ld_warn_execstack value when
>         --enable-warn-execstack=no is given.
>         * configure: Regenerate
>         * testsuite/ld-elf/elf.exp: Add --warn-execstack to ensure
>         the warning is always shown.

Thanks for the patch, but I'm suspicious of the testsuite change and I
think we need a little more here.  I agree a change is needed to make
ld/bfd values consistent but I'm going to jump the other way, changing
link_info.warn_execstack.  Making it consistent that way is nicer in
that the flag becomes an "extended" boolean, ie. 0 => don't warn,
1 => always warn, 2 or 3 => conditional warning depending on
link_info.execstack.

Testing still in progress, I'll commit this shortly if I don't
discover the need for a testsuite change.

bfd/
	* elflink.c (bfd_elf_size_dynamic_sections): Adjust
	warn_execstack test.
include/
	* bfdlink.h (warn_execstack): Swap 0 and 2 meaning.
ld/
	* configure.ac (DEFAULT_LD_WARN_EXECSTACK): Use values of 0,
	1, 2 consistent with link_info.warn_execstack.
	* ld.texi: Typo fixes.
	* lexsup.c (parse_args): Adjust setting of link_info.warn_execstack.
	(elf_static_list_options): Adjust help message conditions.
	* configure: Regenerate.

diff --git a/bfd/elflink.c b/bfd/elflink.c
index 4d6fe663f68..96eb36aa5bf 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -7179,7 +7179,7 @@ warning: enabling an executable stack because of -z execstack command line optio
 	{
 	  if (exec)
 	    {
-	      if (info->warn_execstack != 2)
+	      if (info->warn_execstack != 0)
 		{
 		  /* PR 29072: Because an executable stack is a serious
 		     security risk, make sure that the user knows that it is
diff --git a/include/bfdlink.h b/include/bfdlink.h
index 27a8e11cc22..09a3ec01685 100644
--- a/include/bfdlink.h
+++ b/include/bfdlink.h
@@ -493,12 +493,9 @@ struct bfd_link_info
   unsigned int noexecstack: 1;
 
   /* Tri-state variable:
-     0 => warn if the linker is creating an executable stack, but
-     execstack (above) is 0.
-     1 => warn if the linker is creating an executable stack; ignores
-     the value of execstack.
-     2 => do not warn.
-     3 => not used.  */
+     0 => do not warn when creating an executable stack.
+     1 => always warn when creating an executable stack.
+     >1 => warn when creating an executable stack if execstack is 0.  */
   unsigned int warn_execstack: 2;
 
   /* TRUE if warnings should not be generated for TLS segments with eXecute
diff --git a/ld/configure b/ld/configure
index b4b0ce14ed9..16db825d5ab 100755
--- a/ld/configure
+++ b/ld/configure
@@ -15438,12 +15438,14 @@ fi
 
 
 
-ac_default_ld_warn_execstack=unset
+# By default warn when an executable stack is created due to object files
+# requesting such, not when the user specifies -z execstack.
+ac_default_ld_warn_execstack=2
 # Check whether --enable-warn-execstack was given.
 if test "${enable_warn_execstack+set}" = set; then :
   enableval=$enable_warn_execstack; case "${enableval}" in
   yes) ac_default_ld_warn_execstack=1 ;;
-  no)  ac_default_ld_warn_execstack=-1 ;;
+  no)  ac_default_ld_warn_execstack=0 ;;
 esac
 fi
 
@@ -16997,9 +16999,6 @@ _ACEOF
 
 
 
-if test "${ac_default_ld_warn_execstack}" = unset; then
-  ac_default_ld_warn_execstack=0
-fi
 
 cat >>confdefs.h <<_ACEOF
 #define DEFAULT_LD_WARN_EXECSTACK $ac_default_ld_warn_execstack
diff --git a/ld/configure.ac b/ld/configure.ac
index 0b29e810dde..01121480c6d 100644
--- a/ld/configure.ac
+++ b/ld/configure.ac
@@ -204,13 +204,15 @@ AC_ARG_ENABLE(separate-code,
 esac])
 
 
-ac_default_ld_warn_execstack=unset
+# By default warn when an executable stack is created due to object files
+# requesting such, not when the user specifies -z execstack.
+ac_default_ld_warn_execstack=2
 AC_ARG_ENABLE(warn-execstack,
 	      AS_HELP_STRING([--enable-warn-execstack],
 	      [enable warnings when creating an executable stack]),
 [case "${enableval}" in
   yes) ac_default_ld_warn_execstack=1 ;;
-  no)  ac_default_ld_warn_execstack=-1 ;;
+  no)  ac_default_ld_warn_execstack=0 ;;
 esac])
 
 ac_default_ld_warn_rwx_segments=unset
@@ -531,9 +533,6 @@ AC_DEFINE_UNQUOTED(DEFAULT_LD_Z_SEPARATE_CODE,
   [Define to 1 if you want to enable -z separate-code in ELF linker by default.])
 
 
-if test "${ac_default_ld_warn_execstack}" = unset; then
-  ac_default_ld_warn_execstack=0
-fi
 AC_DEFINE_UNQUOTED(DEFAULT_LD_WARN_EXECSTACK,
   $ac_default_ld_warn_execstack,
   [Define to 1 if you want to enable --warn-execstack in ELF linker by default.])
diff --git a/ld/ld.texi b/ld/ld.texi
index 8cad8478140..a2b162ce5b5 100644
--- a/ld/ld.texi
+++ b/ld/ld.texi
@@ -2654,7 +2654,7 @@ object file formats.  For formats like COFF or ELF, the linker can not
 detect the use of global constructors.
 
 @kindex --warn-execstack
-@cindex warnings, on exectuable stack
+@cindex warnings, on executable stack
 @cindex executable stack, warnings on
 @item --warn-execstack
 @itemx --no-warn-execstack
@@ -2667,7 +2667,7 @@ line option has been used, but this behaviour can be overridden by the
 On the other hand the linker will normally warn if the stack is made
 executable because one or more of the input files need an execuable
 stack and neither of the @command{-z execstack} or @command{-z
-noexecstack} comman line options have been specified.  This warning
+noexecstack} command line options have been specified.  This warning
 can be disabled via the @command{--no-warn-execstack} option.
 
 Note: ELF format input files specify that they need an executable
diff --git a/ld/lexsup.c b/ld/lexsup.c
index 78190472907..82c459adb51 100644
--- a/ld/lexsup.c
+++ b/ld/lexsup.c
@@ -927,7 +927,7 @@ parse_args (unsigned argc, char **argv)
 	  link_info.warn_execstack = 1;
 	  break;
 	case OPTION_NO_WARN_EXECSTACK:
-	  link_info.warn_execstack = 2;
+	  link_info.warn_execstack = 0;
 	  break;
 	case OPTION_WARN_RWX_SEGMENTS:
 	  link_info.no_warn_rwx_segments = 0;
@@ -2169,14 +2169,14 @@ elf_static_list_options (FILE *file)
   -z execstack                Mark executable as requiring executable stack\n"));
   fprintf (file, _("\
   -z noexecstack              Mark executable as not requiring executable stack\n"));
-#if DEFAULT_LD_WARN_EXECSTACK > 0
+#if DEFAULT_LD_WARN_EXECSTACK == 1
   fprintf (file, _("\
   --warn-execstack            Generate a warning if the stack is executable (default)\n"));
 #else
   fprintf (file, _("\
   --warn-execstack            Generate a warning if the stack is executable\n"));
 #endif
-#if DEFAULT_LD_WARN_EXECSTACK < 0
+#if DEFAULT_LD_WARN_EXECSTACK == 0
   fprintf (file, _("\
   --no-warn-execstack         Do not generate a warning if the stack is executable (default)\n"));
 #else

-- 
Alan Modra
Australia Development Lab, IBM