5.10-stable patches

added patches:
	drm-edid-fix-objtool-warning-in-drm_cvt_modes.patch

diff --git a/queue-5.10/drm-edid-fix-objtool-warning-in-drm_cvt_modes.patch b/queue-5.10/drm-edid-fix-objtool-warning-in-drm_cvt_modes.patch
new file mode 100644 (file)
index 0000000..6407b47
--- /dev/null
+++ b/queue-5.10/drm-edid-fix-objtool-warning-in-drm_cvt_modes.patch
@@ -0,0 +1,91 @@
+From d652d5f1eeeb06046009f4fcb9b4542249526916 Mon Sep 17 00:00:00 2001
+From: Linus Torvalds <torvalds@linux-foundation.org>
+Date: Thu, 17 Dec 2020 09:27:57 -0800
+Subject: drm/edid: fix objtool warning in drm_cvt_modes()
+
+From: Linus Torvalds <torvalds@linux-foundation.org>
+
+commit d652d5f1eeeb06046009f4fcb9b4542249526916 upstream.
+
+Commit 991fcb77f490 ("drm/edid: Fix uninitialized variable in
+drm_cvt_modes()") just replaced one warning with another.
+
+The original warning about a possibly uninitialized variable was due to
+the compiler not being smart enough to see that the case statement
+actually enumerated all possible cases.  And the initial fix was just to
+add a "default" case that had a single "unreachable()", just to tell the
+compiler that that situation cannot happen.
+
+However, that doesn't actually fix the fundamental reason for the
+problem: the compiler still doesn't see that the existing case
+statements enumerate all possibilities, so the compiler will still
+generate code to jump to that unreachable case statement.  It just won't
+complain about an uninitialized variable any more.
+
+So now the compiler generates code to our inline asm marker that we told
+it would not fall through, and end end result is basically random.  We
+have created a bridge to nowhere.
+
+And then, depending on the random details of just exactly what the
+compiler ends up doing, 'objtool' might end up complaining about the
+conditional branches (for conditions that cannot happen, and that thus
+will never be taken - but if the compiler was not smart enough to figure
+that out, we can't expect objtool to do so) going off in the weeds.
+
+So depending on how the compiler has laid out the result, you might see
+something like this:
+
+    drivers/gpu/drm/drm_edid.o: warning: objtool: do_cvt_mode() falls through to next function drm_mode_detailed.isra.0()
+
+and now you have a truly inscrutable warning that makes no sense at all
+unless you start looking at whatever random code the compiler happened
+to generate for our bare "unreachable()" statement.
+
+IOW, don't use "unreachable()" unless you have an _active_ operation
+that generates code that actually makes it obvious that something is not
+reachable (ie an UD instruction or similar).
+
+Solve the "compiler isn't smart enough" problem by just marking one of
+the cases as "default", so that even when the compiler doesn't otherwise
+see that we've enumerated all cases, the compiler will feel happy and
+safe about there always being a valid case that initializes the 'width'
+variable.
+
+This also generates better code, since now the compiler doesn't generate
+comparisons for five different possibilities (the four real ones and the
+one that can't happen), but just for the three real ones and "the rest"
+(which is that last one).
+
+A smart enough compiler that sees that we cover all the cases won't care.
+
+Cc: Lyude Paul <lyude@redhat.com>
+Cc: Ilia Mirkin <imirkin@alum.mit.edu>
+Cc: Josh Poimboeuf <jpoimboe@redhat.com>
+Cc: Peter Zijlstra <peterz@infradead.org>
+Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ drivers/gpu/drm/drm_edid.c |    4 ++--
+ 1 file changed, 2 insertions(+), 2 deletions(-)
+
+--- a/drivers/gpu/drm/drm_edid.c
++++ b/drivers/gpu/drm/drm_edid.c
+@@ -3102,6 +3102,8 @@ static int drm_cvt_modes(struct drm_conn
+ 
+               height = (cvt->code[0] + ((cvt->code[1] & 0xf0) << 4) + 1) * 2;
+               switch (cvt->code[1] & 0x0c) {
++              /* default - because compiler doesn't see that we've enumerated all cases */
++              default:
+               case 0x00:
+                       width = height * 4 / 3;
+                       break;
+@@ -3114,8 +3116,6 @@ static int drm_cvt_modes(struct drm_conn
+               case 0x0c:
+                       width = height * 15 / 9;
+                       break;
+-              default:
+-                      unreachable();
+               }
+ 
+               for (j = 1; j < 5; j++) {

diff --git a/queue-5.10/series b/queue-5.10/series
index 5564bf45d6f541785bd93a0485b307b55ccbe6d6..284ea689d979a6b4603526875f45931e553cba3c 100644 (file)
--- a/queue-5.10/series
+++ b/queue-5.10/series
@@ -715,3 +715,4 @@ rtc-ep93xx-fix-null-pointer-dereference-in-ep93xx_rtc_read_time.patch
 revert-ring-buffer-remove-have_64bit_aligned_access.patch
 null_blk-fix-zone-size-initialization.patch
 null_blk-fail-zone-append-to-conventional-zones.patch
+drm-edid-fix-objtool-warning-in-drm_cvt_modes.patch