kconfig: re-sync with Linux 4.17-rc4

Align Kconfig to Linux 4.17-rc4 with minimal impact on non-kconfig files.

Previous Kconfig sync was done by commit bf7ab1e70fd762 ("kconfig:
re-sync with Linux 4.10") and it achieved almost perfect alignment with
a few (intended) exceptions, caused by below U-boot commits:

[A] v2015.04 5f9eb2207500 ("kbuild: remove scripts/multiconfig.sh")
[B] v2015.07 20c20826efab ("Kconfig: Enable usage of escape char '\' in string values")
[C] v2016.01 da58dec86616 ("Various Makefiles: Add SPDX-License-Identifier tags")
[D] v2016.03 5b8031ccb4ed ("Add more SPDX-License-Identifier tags")
[E] v2016.03 192bc6948b02 ("Fix GCC format-security errors and convert sprintfs.")

Here is the list of Kconfig commits which followed the v4.10 alignment:

[F] v2018.01 0931ed3c0d0f ("kconfig/symbol.c: use correct pointer type argument for sizeof")
[G] v2018.03 1414e09b4f25 ("kconfig: revert change that was not needed for -Wformat-security")
[H] v2018.05 83d290c56fab ("SPDX: Convert all of our single license tags to Linux Kernel style")

Commit [F] was subsequently applied to Linux kernel as commit [I]
with the same patch id, so it won't contribute to further misalignment.

[I] v4.15-rc1 88127dae6ed9 ("kconfig/symbol.c: use correct pointer type argument for sizeof")

Commit [G] is a Kconfig-specific revert of commit [E].
Commit [H] relocated and reformatted the license doing no functional change.

In summary, the only functional change that makes U-boot Kconfig
diverge from Linux Kconfig is commit [B]. After a brief analysis,
the purpose of [B] seems to be placing "\n" literals in string symbols
like CONFIG_AUTOBOOT_PROMPT="autoboot in %d seconds\n" in order to pass
them directly to printf and expect correct output at runtime. Currently,
Linux doesn't seem to have this requirement, so for the moment [B] looks
like a U-boot specific feature/fix. From point of view of further Kconfig
alignment and backporting efforts, it is highly desired that commits
like [B] are propagated to Linux and any Kconfig fixes/features are
contributed to Linux kernel first. This specific Kconfig re-sync just
keeps [B] in place.

Contrary to 4.10 Kconfig re-sync (which achieves zero non-kconfig
changes), 4.17-rc4 re-sync does some amount of updates in Kbuild
(striving to keep them at minimum), due to a number of reasons:
* Kbuild is affected by the removal of Kconfig "*shipped" files and now
  requires flex and bison pre-installed on the host.
* PYTHON{2,3} variables are defined in top-level Makefile as
  prerequisite for running the newly developed Kconfig unit tests.
* silentoldconfig becomes an "internal implementation detail" deprecated
  for external use, being renamed to syncconfig.

The exact non-kconfig files touched by this commit are:

$ git show --format="" --stat -- ':!scripts/kconfig'
 .gitignore             |  2 ++
 Makefile               |  9 +++++++--
 scripts/Makefile.build | 11 +++++++++++
 scripts/Makefile.lib   | 41 ++++++++++++-----------------------------

The imported Linux commits touching the above files are:

c054be10ffdbd5   ("remove gperf left-overs from build system")
73a4f6dbe70a1b   ("kbuild: add LEX and YACC variables")
033dba2ec06c47   ("kbuild: prepare to remove C files pre-generated by flex and bison")
eea199b445f64c   ("kbuild: remove unnecessary LEX_PREFIX and YACC_PREFIX")
e71de5ee08dcb0   ("kbuild: remove remaining use of undefined YACC_PREFIX")
d59fbbd09d5d6b   ("kbuild: replace hardcoded bison in cmd_bison_h with $(YACC)")
911a91c39cabcb H ("kconfig: rename silentoldconfig to syncconfig")
59889300274569   (".gitignore: move *.lex.c *.tab.[ch] patterns to the top-level .gitignore")
9a8dfb394c0467   ("kbuild: clean up *.lex.c and *.tab.[ch] patterns from top-level Makefile")
833e622459432e H ("genksyms: generate lexer and parser during build instead of shipping")
b23d1a241f4eb4 H ("kbuild: add %.lex.c and %.tab.[ch] to 'targets' automatically")
e9781b52d4e0e3 H ("kbuild: add PYTHON2 and PYTHON3 variables")

The commits marked with 'H' are assessed as "hard" (build will fail)
prerequisites and the rest of them are assessed as "soft" prerequisites
for the re-sync. In spite of relatively high number of non-H commits,
they belong to this Kconfig update topic-wise and decrease the number of
cherry pick conflicts for many commits in this series. Additional effort
can be put in eliminating the soft prerequisites, if really needed.

The commits which contributed to this Kconfig re-sync are listed below.
Whenever a conflict resolution has been performed (mostly by hand, but
sometimes automatically by git), it is revealed by the '!' sign in the
second column, which means a patch id mismatch between Linux and U-boot
commits:

9be3213b14d44f   ("gconfig: remove misleading parentheses around a condition")
ff85a1a80e0034   ("kconfig: Check for libncurses before menuconfig")
ad8181060788c8   ("kconfig: fix sparse warnings in nconfig")
cb77f0d623ff33 ! ("scripts: Switch to more portable Perl shebang")
bb3290d91695bb ! ("Remove gperf usage from toolchain")
c054be10ffdbd5   ("remove gperf left-overs from build system")
b24413180f5600 ! ("License cleanup: add SPDX GPL-2.0 license identifier to files with no license")
9059a3493efea6 ! ("kconfig: fix relational operators for bool and tristate symbols")
2c37e08464a850   ("kconfig: Warn if choice default is not in choice")
33ca1a24866373   ("kconfig: Document the 'menu' struct")
52aede4ba5efd1   ("kconfig: Document the 'symbol' struct")
c873443430ebd1   ("kconfig: Sync zconf.y with zconf.tab.c_shipped")
9a826842ff2fbd   ("kconfig: Rename menu_check_dep() to rewrite_m()")
fa8cedaef814ce   ("kconfig: Clarify expression rewriting")
f77850d3fe0c96   ("kconfig: Clean up modules handling and fix crash")
e3b03bf29d6b99   ("kconfig: display recursive dependency resolution hint just once")
73a4f6dbe70a1b ! ("kbuild: add LEX and YACC variables")
033dba2ec06c47 ! ("kbuild: prepare to remove C files pre-generated by flex and bison")
29c833061c1d8c   ("kconfig: generate lexer and parser during build instead of shipping")
26e47a3c11a25c   ("kconfig: Don't leak symbol names during parsing")
24161a6711c945   ("kconfig: Don't leak 'source' filenames during parsing")
bc28fe1d5ede88   ("kconfig: Don't leak 'option' arguments during parsing")
0724a7c32a54e3   ("kconfig: Don't leak main menus during parsing")
ae7440ef0c8013   ("kconfig: Fix automatic menu creation mem leak")
5b1374b3b3c2fc   ("kconfig: Fix expr_free() E_NOT leak")
7cf33f88e29410   ("kconfig: Fix choice symbol expression leak")
05cccce580456d   ("kconfig: Document automatic submenu creation code")
0735f7e5def2ab   ("kconfig: Document important expression functions")
df60f4b92d3d0b   ("kconfig: Remove menu_end_entry()")
b92d804a51796b   ("kconfig: drop 'boolean' keyword")
6479f327dea60d   ("kconfig: Warn if there is more than one help text")
52e58a3caeba5d   ("kconfig: make input_mode static")
5a3dc717b3c785   ("kconfig: make xfgets() really static")
84dd95d4f87a0d   ("kconfig: make conf_unsaved a local variable of conf_read()")
765f4cdef6f80d   ("kconfig: use default 'yy' prefix for lexer and parser")
eea199b445f64c   ("kbuild: remove unnecessary LEX_PREFIX and YACC_PREFIX")
e71de5ee08dcb0   ("kbuild: remove remaining use of undefined YACC_PREFIX")
d59fbbd09d5d6b ! ("kbuild: replace hardcoded bison in cmd_bison_h with $(YACC)")
3e41ba05b6d60c   ("kconfig: Document SYMBOL_OPTIONAL logic")
d3465af60f4471   ("kconfig: Clarify choice dependency propagation")
9d1a9e8bc18bea   ("kconfig: Document 'if' flattening logic")
b53688014e3325   ("kconfig: Clarify menu and 'if' dependency propagation")
d0fd0428ecf04b   ("kconfig: fix make xconfig when gettext is missing")
312ee68752faaa   ("kconfig: announce removal of oldnoconfig if used")
1ccb27143360bd   ("kconfig: make "Selected by:" and "Implied by:" readable")
cedd55d49dee94 ! ("kconfig: Remove silentoldconfig from help and docs; fix kconfig/conf's help")
1b9eda2e4892cb   ("kconfig: Warn if help text is blank")
cb67ab2cd2b8ab   ("kconfig: do not write choice values when their dependency becomes n")
4f208f392103e8   ("kconfig: show '?' prompt even if no help text is available")
cd58a91def2acc   ("kconfig: remove 'config*' pattern from .gitignnore")
d2a04648a5dbc3   ("kconfig: remove check_stdin()")
f3ff6fb5db68bc   ("kconfig: echo stdin to stdout if either is redirected")
9e3e10c725360b   ("kconfig: send error messages to stderr")
d717f24d8c6808   ("kconfig: add xrealloc() helper")
523ca58b7db2e3   ("kconfig: remove const qualifier from sym_expand_string_value()")
cd81fc82b93fa4   ("kconfig: add xstrdup() helper")
f4bc1eefc1608e   ("kconfig: set SYMBOL_AUTO to the symbol marked with defconfig_list")
bf0bbdcf100322   ("kconfig: Don't leak choice names during parsing")
1a90ce36c6eff6   ("kconfig: Update ncurses package names for menuconfig")
5ae6fcc4bb82bd   ("kconfig: fix line number in recursive inclusion error message")
07a422bb213adb ! ("kbuild: restore autoksyms.h touch to the top Makefile")
9a47ceec543bfb   ("kconfig: clean-up reverse dependency help implementation")
d9119b5925a03b   ("kconfig: Print reverse dependencies in groups")
f467c5640c29ad   ("kconfig: only write '# CONFIG_FOO is not set' for visible symbols")
59a80b5e892dde   ("kconfig: do not call check_conf() for olddefconfig")
4bb3a5b085cd6f   ("kconfig: remove unneeded input_mode test in conf()")
99f0b6578bab44   ("kconfig: remove redundant input_mode test for check_conf() loop")
2aad9b89621386   ("kconfig: hide irrelevant sub-menus for oldconfig")
81d2bc2273052e   ("kconfig: invoke oldconfig instead of silentoldconfig from local*config")
911a91c39cabcb ! ("kconfig: rename silentoldconfig to syncconfig")
2a61625835c7c8 ! ("kconfig: remove redundant streamline_config.pl prerequisite")
022a4bf6b59dfd   ("kconfig: tests: add framework for Kconfig unit testing")
1903c511905984   ("kconfig: tests: add basic choice tests")
49ac3c0c3aa3b7   ("kconfig: tests: test automatic submenu creation")
b76960c0f6b25d   ("kconfig: tests: test if new symbols in choice are asked")
930c429a656fdb   ("kconfig: tests: check unneeded "is not set" with unmet dependency")
ee236610653ede   ("kconfig: tests: check visibility of tristate choice values in y choice")
beaaddb625400e   ("kconfig: tests: test defconfig when two choices interact")
3e4888c2e3d77d   ("kconfig: tests: test randconfig for choice in choice")
29c434f367ea7b   ("kconfig: tests: test if recursive dependencies are detected")
e2c75e7667c737   ("kconfig: tests: test if recursive inclusion is detected")
f622f827958162   ("kconfig: warn unmet direct dependency of tristate symbols selected by y")
f8f69dc0b4e070   ("kconfig: make unmet dependency warnings readable")
26561514cc9def   ("kconfig: do not include both curses.h and ncurses.h for nconfig")
32a94b8b0c3e5a   ("kconfig: remove duplicated file name and lineno of recursive inclusion")
379a8eb8eb1a55   ("kconfig: detect recursive inclusion earlier")
18492685e479fd   ("kconfig: use yylineno option instead of manual lineno increments")
59889300274569 ! (".gitignore: move *.lex.c *.tab.[ch] patterns to the top-level .gitignore")
9a8dfb394c0467 ! ("kbuild: clean up *.lex.c and *.tab.[ch] patterns from top-level Makefile")
833e622459432e ! ("genksyms: generate lexer and parser during build instead of shipping")
b23d1a241f4eb4 ! ("kbuild: add %.lex.c and %.tab.[ch] to 'targets' automatically")
17baab68d337a0   ("kconfig: extend output of 'listnewconfig'")
e9781b52d4e0e3 ! ("kbuild: add PYTHON2 and PYTHON3 variables")

The current Kconfig update generates below build-time warnings:
  YACC    scripts/dtc/dtc-parser.tab.h
scripts/dtc/dtc-parser.y: warning: 3 shift/reduce conflicts [-Wconflicts-sr]
  YACC    scripts/dtc/dtc-parser.tab.c
scripts/dtc/dtc-parser.y: warning: 3 shift/reduce conflicts [-Wconflicts-sr]

This seems to happen because the Kbuild updates apparently didn't make
room for both "*shipped"-based builds and flex/bison-based builds. A
similar problem has been reported for genksyms parser in v4.17-rc1
commit 833e622459432e ("genksyms: generate lexer and parser during build
instead of shipping"). I have figured out empirically that the warnings
are healed after updating the in-tree U-boot DTC to upstream v1.4.6-9,
same as done by Linux v4.17-rc1 commit 9130ba88464032 ("scripts/dtc:
Update to upstream version v1.4.6-9-gaadd0b65c987"). Whether fixing the
DTC-related yacc warnings should be done together with the Kconfig
re-sync, I would like to hear from community.

My testing was limited to:
- make defconfig all
- make ARCH=arm CROSS_COMPILE=aarch64-linux-gnu- r8a7795_ulcb_defconfig all
- comparing .config before and after the re-sync
- running the newly imported Kconfig unit tests as seen below:

$ make testconfig
Tested-by: Petr Vorel <petr.vorel@gmail.com>

============================= test session starts =============================
scripts/kconfig/tests/auto_submenu/__init__.py::test PASSED             [  7%]
scripts/kconfig/tests/choice/__init__.py::test_oldask0 PASSED           [ 14%]
scripts/kconfig/tests/choice/__init__.py::test_oldask1 PASSED           [ 21%]
scripts/kconfig/tests/choice/__init__.py::test_allyes PASSED            [ 28%]
scripts/kconfig/tests/choice/__init__.py::test_allmod PASSED            [ 35%]
scripts/kconfig/tests/choice/__init__.py::test_allno PASSED             [ 42%]
scripts/kconfig/tests/choice/__init__.py::test_alldef PASSED            [ 50%]
scripts/kconfig/tests/choice_value_with_m_dep/__init__.py::test PASSED  [ 57%]
scripts/kconfig/tests/err_recursive_inc/__init__.py::test PASSED        [ 64%]
scripts/kconfig/tests/inter_choice/__init__.py::test PASSED             [ 71%]
scripts/kconfig/tests/new_choice_with_dep/__init__.py::test PASSED      [ 78%]
scripts/kconfig/tests/no_write_if_dep_unmet/__init__.py::test PASSED    [ 85%]
scripts/kconfig/tests/rand_nested_choice/__init__.py::test PASSED       [ 92%]
scripts/kconfig/tests/warn_recursive_dep/__init__.py::test PASSED       [100%]
========================== 14 passed in 0.34 seconds ==========================

Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>
Reviewed-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Tested-by: Petr Vorel <petr.vorel@gmail.com>

1 files changed, 146 insertions, 47 deletions

diff --git a/scripts/kconfig/expr.c b/scripts/kconfig/expr.c
index cbf4996dd9..e1a39e9084 100644
--- a/scripts/kconfig/expr.c
+++ b/scripts/kconfig/expr.c
@@ -94,7 +94,7 @@ struct expr *expr_copy(const struct expr *org)
 		e->right.expr = expr_copy(org->right.expr);
 		break;
 	default:
-		printf("can't copy type %d\n", e->type);
+		fprintf(stderr, "can't copy type %d\n", e->type);
 		free(e);
 		e = NULL;
 		break;
@@ -113,7 +113,7 @@ void expr_free(struct expr *e)
 		break;
 	case E_NOT:
 		expr_free(e->left.expr);
-		return;
+		break;
 	case E_EQUAL:
 	case E_GEQ:
 	case E_GTH:
@@ -127,7 +127,7 @@ void expr_free(struct expr *e)
 		expr_free(e->right.expr);
 		break;
 	default:
-		printf("how to free type %d?\n", e->type);
+		fprintf(stderr, "how to free type %d?\n", e->type);
 		break;
 	}
 	free(e);
@@ -138,8 +138,18 @@ static int trans_count;
 #define e1 (*ep1)
 #define e2 (*ep2)
 
+/*
+ * expr_eliminate_eq() helper.
+ *
+ * Walks the two expression trees given in 'ep1' and 'ep2'. Any node that does
+ * not have type 'type' (E_OR/E_AND) is considered a leaf, and is compared
+ * against all other leaves. Two equal leaves are both replaced with either 'y'
+ * or 'n' as appropriate for 'type', to be eliminated later.
+ */
 static void __expr_eliminate_eq(enum expr_type type, struct expr **ep1, struct expr **ep2)
 {
+	/* Recurse down to leaves */
+
 	if (e1->type == type) {
 		__expr_eliminate_eq(type, &e1->left.expr, &e2);
 		__expr_eliminate_eq(type, &e1->right.expr, &e2);
@@ -150,12 +160,18 @@ static void __expr_eliminate_eq(enum expr_type type, struct expr **ep1, struct e
 		__expr_eliminate_eq(type, &e1, &e2->right.expr);
 		return;
 	}
+
+	/* e1 and e2 are leaves. Compare them. */
+
 	if (e1->type == E_SYMBOL && e2->type == E_SYMBOL &&
 	    e1->left.sym == e2->left.sym &&
 	    (e1->left.sym == &symbol_yes || e1->left.sym == &symbol_no))
 		return;
 	if (!expr_eq(e1, e2))
 		return;
+
+	/* e1 and e2 are equal leaves. Prepare them for elimination. */
+
 	trans_count++;
 	expr_free(e1); expr_free(e2);
 	switch (type) {
@@ -172,6 +188,35 @@ static void __expr_eliminate_eq(enum expr_type type, struct expr **ep1, struct e
 	}
 }
 
+/*
+ * Rewrites the expressions 'ep1' and 'ep2' to remove operands common to both.
+ * Example reductions:
+ *
+ *	ep1: A && B           ->  ep1: y
+ *	ep2: A && B && C      ->  ep2: C
+ *
+ *	ep1: A || B           ->  ep1: n
+ *	ep2: A || B || C      ->  ep2: C
+ *
+ *	ep1: A && (B && FOO)  ->  ep1: FOO
+ *	ep2: (BAR && B) && A  ->  ep2: BAR
+ *
+ *	ep1: A && (B || C)    ->  ep1: y
+ *	ep2: (C || B) && A    ->  ep2: y
+ *
+ * Comparisons are done between all operands at the same "level" of && or ||.
+ * For example, in the expression 'e1 && (e2 || e3) && (e4 || e5)', the
+ * following operands will be compared:
+ *
+ *	- 'e1', 'e2 || e3', and 'e4 || e5', against each other
+ *	- e2 against e3
+ *	- e4 against e5
+ *
+ * Parentheses are irrelevant within a single level. 'e1 && (e2 && e3)' and
+ * '(e1 && e2) && e3' are both a single level.
+ *
+ * See __expr_eliminate_eq() as well.
+ */
 void expr_eliminate_eq(struct expr **ep1, struct expr **ep2)
 {
 	if (!e1 || !e2)
@@ -197,6 +242,12 @@ void expr_eliminate_eq(struct expr **ep1, struct expr **ep2)
 #undef e1
 #undef e2
 
+/*
+ * Returns true if 'e1' and 'e2' are equal, after minor simplification. Two
+ * &&/|| expressions are considered equal if every operand in one expression
+ * equals some operand in the other (operands do not need to appear in the same
+ * order), recursively.
+ */
 static int expr_eq(struct expr *e1, struct expr *e2)
 {
 	int res, old_count;
@@ -243,6 +294,17 @@ static int expr_eq(struct expr *e1, struct expr *e2)
 	return 0;
 }
 
+/*
+ * Recursively performs the following simplifications in-place (as well as the
+ * corresponding simplifications with swapped operands):
+ *
+ *	expr && n  ->  n
+ *	expr && y  ->  expr
+ *	expr || n  ->  expr
+ *	expr || y  ->  y
+ *
+ * Returns the optimized expression.
+ */
 static struct expr *expr_eliminate_yn(struct expr *e)
 {
 	struct expr *tmp;
@@ -516,12 +578,21 @@ static struct expr *expr_join_and(struct expr *e1, struct expr *e2)
 	return NULL;
 }
 
+/*
+ * expr_eliminate_dups() helper.
+ *
+ * Walks the two expression trees given in 'ep1' and 'ep2'. Any node that does
+ * not have type 'type' (E_OR/E_AND) is considered a leaf, and is compared
+ * against all other leaves to look for simplifications.
+ */
 static void expr_eliminate_dups1(enum expr_type type, struct expr **ep1, struct expr **ep2)
 {
 #define e1 (*ep1)
 #define e2 (*ep2)
 	struct expr *tmp;
 
+	/* Recurse down to leaves */
+
 	if (e1->type == type) {
 		expr_eliminate_dups1(type, &e1->left.expr, &e2);
 		expr_eliminate_dups1(type, &e1->right.expr, &e2);
@@ -532,6 +603,9 @@ static void expr_eliminate_dups1(enum expr_type type, struct expr **ep1, struct
 		expr_eliminate_dups1(type, &e1, &e2->right.expr);
 		return;
 	}
+
+	/* e1 and e2 are leaves. Compare and process them. */
+
 	if (e1 == e2)
 		return;
 
@@ -568,6 +642,17 @@ static void expr_eliminate_dups1(enum expr_type type, struct expr **ep1, struct
 #undef e2
 }
 
+/*
+ * Rewrites 'e' in-place to remove ("join") duplicate and other redundant
+ * operands.
+ *
+ * Example simplifications:
+ *
+ *	A || B || A    ->  A || B
+ *	A && B && A=y  ->  A=y && B
+ *
+ * Returns the deduplicated expression.
+ */
 struct expr *expr_eliminate_dups(struct expr *e)
 {
 	int oldcount;
@@ -584,6 +669,7 @@ struct expr *expr_eliminate_dups(struct expr *e)
 			;
 		}
 		if (!trans_count)
+			/* No simplifications done in this pass. We're done */
 			break;
 		e = expr_eliminate_yn(e);
 	}
@@ -591,6 +677,12 @@ struct expr *expr_eliminate_dups(struct expr *e)
 	return e;
 }
 
+/*
+ * Performs various simplifications involving logical operators and
+ * comparisons.
+ *
+ * Allocates and returns a new expression.
+ */
 struct expr *expr_transform(struct expr *e)
 {
 	struct expr *tmp;
@@ -805,6 +897,20 @@ bool expr_depends_symbol(struct expr *dep, struct symbol *sym)
  	return false;
 }
 
+/*
+ * Inserts explicit comparisons of type 'type' to symbol 'sym' into the
+ * expression 'e'.
+ *
+ * Examples transformations for type == E_UNEQUAL, sym == &symbol_no:
+ *
+ *	A              ->  A!=n
+ *	!A             ->  A=n
+ *	A && B         ->  !(A=n || B=n)
+ *	A || B         ->  !(A=n && B=n)
+ *	A && (B || C)  ->  !(A=n || (B=n && C=n))
+ *
+ * Allocates and returns a new expression.
+ */
 struct expr *expr_trans_compare(struct expr *e, enum expr_type type, struct symbol *sym)
 {
 	struct expr *e1, *e2;
@@ -893,7 +999,10 @@ static enum string_value_kind expr_parse_string(const char *str,
 	switch (type) {
 	case S_BOOLEAN:
 	case S_TRISTATE:
-		return k_string;
+		val->s = !strcmp(str, "n") ? 0 :
+			 !strcmp(str, "m") ? 1 :
+			 !strcmp(str, "y") ? 2 : -1;
+		return k_signed;
 	case S_INT:
 		val->s = strtoll(str, &tail, 10);
 		kind = k_signed;
@@ -1028,49 +1137,9 @@ static int expr_compare_type(enum expr_type t1, enum expr_type t2)
 	return 0;
 }
 
-static inline struct expr *
-expr_get_leftmost_symbol(const struct expr *e)
-{
-
-	if (e == NULL)
-		return NULL;
-
-	while (e->type != E_SYMBOL)
-		e = e->left.expr;
-
-	return expr_copy(e);
-}
-
-/*
- * Given expression `e1' and `e2', returns the leaf of the longest
- * sub-expression of `e1' not containing 'e2.
- */
-struct expr *expr_simplify_unmet_dep(struct expr *e1, struct expr *e2)
-{
-	struct expr *ret;
-
-	switch (e1->type) {
-	case E_OR:
-		return expr_alloc_and(
-		    expr_simplify_unmet_dep(e1->left.expr, e2),
-		    expr_simplify_unmet_dep(e1->right.expr, e2));
-	case E_AND: {
-		struct expr *e;
-		e = expr_alloc_and(expr_copy(e1), expr_copy(e2));
-		e = expr_eliminate_dups(e);
-		ret = (!expr_eq(e, e1)) ? e1 : NULL;
-		expr_free(e);
-		break;
-		}
-	default:
-		ret = e1;
-		break;
-	}
-
-	return expr_get_leftmost_symbol(ret);
-}
-
-void expr_print(struct expr *e, void (*fn)(void *, struct symbol *, const char *), void *data, int prevtoken)
+void expr_print(struct expr *e,
+		void (*fn)(void *, struct symbol *, const char *),
+		void *data, int prevtoken)
 {
 	if (!e) {
 		fn(data, NULL, "y");
@@ -1204,3 +1273,33 @@ void expr_gstr_print(struct expr *e, struct gstr *gs)
 {
 	expr_print(e, expr_print_gstr_helper, gs, E_NONE);
 }
+
+/*
+ * Transform the top level "||" tokens into newlines and prepend each
+ * line with a minus. This makes expressions much easier to read.
+ * Suitable for reverse dependency expressions.
+ */
+static void expr_print_revdep(struct expr *e,
+			      void (*fn)(void *, struct symbol *, const char *),
+			      void *data, tristate pr_type, const char **title)
+{
+	if (e->type == E_OR) {
+		expr_print_revdep(e->left.expr, fn, data, pr_type, title);
+		expr_print_revdep(e->right.expr, fn, data, pr_type, title);
+	} else if (expr_calc_value(e) == pr_type) {
+		if (*title) {
+			fn(data, NULL, *title);
+			*title = NULL;
+		}
+
+		fn(data, NULL, "  - ");
+		expr_print(e, fn, data, E_NONE);
+		fn(data, NULL, "\n");
+	}
+}
+
+void expr_gstr_print_revdep(struct expr *e, struct gstr *gs,
+			    tristate pr_type, const char *title)
+{
+	expr_print_revdep(e, expr_print_gstr_helper, gs, pr_type, &title);
+}