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Date:   Tue, 23 Feb 2021 17:46:42 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Heiko Carstens <hca@...ux.ibm.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        linux-hardening@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...nel.org>
Subject: Re: [PATCH] gcc-plugins: Disable GCC_PLUGIN_CYC_COMPLEXITY for s390

On Tue, Feb 23, 2021 at 07:03:47PM +0100, Heiko Carstens wrote:
> On Tue, Feb 23, 2021 at 09:41:40AM -0800, Guenter Roeck wrote:
> > > I tried to explain why we don't want to set COMPILE_TEST for s390
> > > anymore. It overrides architecture dependencies in Kconfig, and lots
> > > of drivers do not set dependencies for HAS_IOMEM, HAS_DMA, and friends
> > > correctly.
> > > This generates constantly fallout which is irrelevant for s390 and
> > > also for other architectures. It generates just work with close to
> > > zero benefit. For drivers which matter for s390 we still see those
> > > errors.
> > > 
> > > > On the other side, if that flag would be set explicitly by
> > > > all{yes,mod}config, it would really beg for being misused. We
> > > > might then as well add a new flag that is explicitly associated
> > > > with all{yes,mod}config, but not with randconfig.
> > > 
> > > I think that makes most sense, probably also have a flag that is set
> > > for randconfig.
> > 
> > Not sure what value such an option would have, and how it would be used.
> > I would argue that randconfig should not set COMPILE_TEST to start with,
> > since its purpose should be to test random valid configurations and not
> > to compile test arbitrary (and in that case random) code. But that is
> > a different question, and just my personal opinion.
> > 
> > Overall, the question is what kind of additional option you would find
> > useful for s390. You make it clear that you don't want COMPILE_TEST.
> > At the same time, you still want all{mod,yes}config, but presumably
> > excluding options currently restricted by !COMPILE_TEST (such as
> > DEBUG_INFO, BPF_PRELOAD, UBSAN_TRAP, GCC_PLUGIN_CYC_COMPLEXITY,
> > and a few others). SUPPRESS_NOISY_TESTS would not cover that, but
> > neither would RANDCONFIG (or whatever it would be called).
> 
> Well, if we would have e.g. RANDCONFIG, then we could probably revert
> 334ef6ed06fa ("init/Kconfig: make COMPILE_TEST depend on !S390") and
> instead let COMPILE_TEST depend on !RANDCONFIG.
> I think this _could_ solve all common problems we currently see.
> 
> And it would also do what you suggested.

Sounds good.

Question is how one would set such a flag. The code in scripts/kconfig/conf.c
doesn't really set COMPILE_TEST in conjunction with randconfig; that is
just as random as all other configuration flags. Would something like
the patch below be acceptable ?

Thanks,
Guenter

---
>From 301dc1746b259afce02c104ebbf3f0c37189ae4a Mon Sep 17 00:00:00 2001
From: Guenter Roeck <linux@...ck-us.net>
Date: Tue, 23 Feb 2021 17:21:51 -0800
Subject: [PATCH] kconfig: Introduce RANDCONFIG

"make randconfig" is intended to be used to generate random valid
configurations. It is supposed to verify if configuration dependencies
are valid and compile. It is not supposed to be used as replacement
for all{mod,yes}config.

However, that is not currently the case. "make randconfig" treats all
configurations randomly. This means that "COMPILE_TEST" will be enabled
randomly. This defeats the purpose of "make randconfig"

To solve the problem, introduce a RANDCONFIG configuration option
and set it for all "randconfig" configurations. Disable COMPILE_TEST
whenever RANDCONFIG is enabled.

Signed-off-by: Guenter Roeck <linux@...ck-us.net>
---
 init/Kconfig               | 12 ++++++++++++
 scripts/kconfig/confdata.c | 15 ++++++++++++---
 scripts/kconfig/expr.h     |  1 +
 scripts/kconfig/lexer.l    |  1 +
 scripts/kconfig/lkc.h      |  1 +
 scripts/kconfig/menu.c     |  5 +++++
 scripts/kconfig/parser.y   |  6 ++++++
 7 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index ba8bd5256980..a85099c5e383 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -111,9 +111,21 @@ config INIT_ENV_ARG_LIMIT
 	  Maximum of each of the number of arguments and environment
 	  variables passed to init from the kernel command line.
 
+config RANDCONFIG
+	bool "Compile random configurations"
+	option randconfig_y
+	help
+	  This option indicates that the configuration is random and used to
+	  test if configuration dependencies are valid and complete.
+	  Resulting images are not expected to be bootable on real hardware.
+
+	  If you are a developer and want to build test random configurations,
+	  say Y here. If you are a user/distributor, say N.
+
 config COMPILE_TEST
 	bool "Compile also drivers which will not load"
 	depends on !UML && !S390
+	depends on !RANDCONFIG
 	default n
 	help
 	  Some drivers can be compiled on a different platform than they are
diff --git a/scripts/kconfig/confdata.c b/scripts/kconfig/confdata.c
index 2568dbe16ed6..0b36cc2f702b 100644
--- a/scripts/kconfig/confdata.c
+++ b/scripts/kconfig/confdata.c
@@ -1254,10 +1254,16 @@ bool conf_set_all_new_symbols(enum conf_def_mode mode)
 			has_changed = true;
 			switch (mode) {
 			case def_yes:
-				sym->def[S_DEF_USER].tri = yes;
+				if (sym->flags & SYMBOL_RANDCONFIG_Y)
+					sym->def[S_DEF_USER].tri = no;
+				else
+					sym->def[S_DEF_USER].tri = yes;
 				break;
 			case def_mod:
-				sym->def[S_DEF_USER].tri = mod;
+				if (sym->flags & SYMBOL_RANDCONFIG_Y)
+					sym->def[S_DEF_USER].tri = no;
+				else
+					sym->def[S_DEF_USER].tri = mod;
 				break;
 			case def_no:
 				if (sym->flags & SYMBOL_ALLNOCONFIG_Y)
@@ -1267,7 +1273,10 @@ bool conf_set_all_new_symbols(enum conf_def_mode mode)
 				break;
 			case def_random:
 				sym->def[S_DEF_USER].tri = no;
-				cnt = rand() % 100;
+				if (sym->flags & SYMBOL_RANDCONFIG_Y)
+					cnt = -1;
+				else
+					cnt = rand() % 100;
 				if (sym->type == S_TRISTATE) {
 					if (cnt < pty)
 						sym->def[S_DEF_USER].tri = yes;
diff --git a/scripts/kconfig/expr.h b/scripts/kconfig/expr.h
index 5c3443692f34..70f4acce2b7b 100644
--- a/scripts/kconfig/expr.h
+++ b/scripts/kconfig/expr.h
@@ -158,6 +158,7 @@ struct symbol {
 
 /* Set symbol to y if allnoconfig; used for symbols that hide others */
 #define SYMBOL_ALLNOCONFIG_Y 0x200000
+#define SYMBOL_RANDCONFIG_Y  0x400000
 
 #define SYMBOL_MAXLENGTH	256
 #define SYMBOL_HASHSIZE		9973
diff --git a/scripts/kconfig/lexer.l b/scripts/kconfig/lexer.l
index 9c22cb554673..fd9cd3622ea7 100644
--- a/scripts/kconfig/lexer.l
+++ b/scripts/kconfig/lexer.l
@@ -92,6 +92,7 @@ n	[A-Za-z0-9_-]
 \\\n			/* escaped new line */
 \n			return T_EOL;
 "allnoconfig_y"		return T_ALLNOCONFIG_Y;
+"randconfig_y"		return T_RANDCONFIG_Y;
 "bool"			return T_BOOL;
 "choice"		return T_CHOICE;
 "comment"		return T_COMMENT;
diff --git a/scripts/kconfig/lkc.h b/scripts/kconfig/lkc.h
index bee2413bda63..871a05f887f0 100644
--- a/scripts/kconfig/lkc.h
+++ b/scripts/kconfig/lkc.h
@@ -110,6 +110,7 @@ void menu_add_symbol(enum prop_type type, struct symbol *sym, struct expr *dep);
 void menu_add_option_modules(void);
 void menu_add_option_defconfig_list(void);
 void menu_add_option_allnoconfig_y(void);
+void menu_add_option_randconfig_y(void);
 void menu_finalize(struct menu *parent);
 void menu_set_type(int type);
 
diff --git a/scripts/kconfig/menu.c b/scripts/kconfig/menu.c
index a5fbd6ccc006..5ec3a26566b8 100644
--- a/scripts/kconfig/menu.c
+++ b/scripts/kconfig/menu.c
@@ -233,6 +233,11 @@ void menu_add_option_allnoconfig_y(void)
 	current_entry->sym->flags |= SYMBOL_ALLNOCONFIG_Y;
 }
 
+void menu_add_option_randconfig_y(void)
+{
+	current_entry->sym->flags |= SYMBOL_RANDCONFIG_Y;
+}
+
 static int menu_validate_number(struct symbol *sym, struct symbol *sym2)
 {
 	return sym2->type == S_INT || sym2->type == S_HEX ||
diff --git a/scripts/kconfig/parser.y b/scripts/kconfig/parser.y
index 190f1117f35a..335ce0554c84 100644
--- a/scripts/kconfig/parser.y
+++ b/scripts/kconfig/parser.y
@@ -46,6 +46,7 @@ static struct menu *current_menu, *current_entry;
 %token <string> T_WORD
 %token <string> T_WORD_QUOTE
 %token T_ALLNOCONFIG_Y
+%token T_RANDCONFIG_Y
 %token T_BOOL
 %token T_CHOICE
 %token T_CLOSE_PAREN
@@ -233,6 +234,11 @@ config_option: T_OPTION T_ALLNOCONFIG_Y T_EOL
 	menu_add_option_allnoconfig_y();
 };
 
+config_option: T_OPTION T_RANDCONFIG_Y T_EOL
+{
+	menu_add_option_randconfig_y();
+};
+
 /* choice entry */
 
 choice: T_CHOICE word_opt T_EOL
-- 
2.17.1

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