From:   Asahi Lina <lina@asahilina.net>
To:     Arnd Bergmann <arnd@arndb.de>, Hector Martin <marcan@marcan.st>,
        Sven Peter <sven@svenpeter.dev>
Cc:     Alyssa Rosenzweig <alyssa@rosenzweig.io>, asahi@lists.linux.dev,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Asahi Lina <lina@asahilina.net>
Subject: [PATCH] soc: apple: rtkit: Do not copy the reg state structure to the stack
Date:   Sat, 11 Feb 2023 18:13:02 +0900
Message-Id: <20230211091302.4576-1-lina@asahilina.net>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The register state struct is 848 bytes, which ends up bloating the
apple_rtkit_crashlog_dump_regs stack frame beyond 1024 on some
32-bit platforms, triggering compile warnings.

This doesn't matter for 64BIT/ARM64, but there's also no good reason to
copy the structure to the stack in this case. We can use __packed to
avoid alignment issues, there are no double-read hazards, and this is a
fatal error path so performance does not matter.

Fixes: 22991d8d5725 ("soc: apple: rtkit: Add register dump decoding to crashlog")
Signed-off-by: Asahi Lina <lina@asahilina.net>
---
 drivers/soc/apple/rtkit-crashlog.c | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/drivers/soc/apple/rtkit-crashlog.c b/drivers/soc/apple/rtkit-crashlog.c
index dfa74b32eda2..8319e365110b 100644
--- a/drivers/soc/apple/rtkit-crashlog.c
+++ b/drivers/soc/apple/rtkit-crashlog.c
@@ -57,7 +57,7 @@ struct apple_rtkit_crashlog_regs {
 	u64 unk_X;
 	u64 esr;
 	u64 unk_Z;
-};
+} __packed;
 static_assert(sizeof(struct apple_rtkit_crashlog_regs) == 0x350);
 
 static void apple_rtkit_crashlog_dump_str(struct apple_rtkit *rtk, u8 *bfr,
@@ -126,18 +126,18 @@ static void apple_rtkit_crashlog_dump_mailbox(struct apple_rtkit *rtk, u8 *bfr,
 static void apple_rtkit_crashlog_dump_regs(struct apple_rtkit *rtk, u8 *bfr,
 					   size_t size)
 {
-	struct apple_rtkit_crashlog_regs regs;
+	struct apple_rtkit_crashlog_regs *regs;
 	const char *el;
 	int i;
 
-	if (size < sizeof(regs)) {
+	if (size < sizeof(*regs)) {
 		dev_warn(rtk->dev, "RTKit: Regs section too small: 0x%zx", size);
 		return;
 	}
 
-	memcpy(&regs, bfr, sizeof(regs));
+	regs = (struct apple_rtkit_crashlog_regs *)bfr;
 
-	switch (regs.psr & PSR_MODE_MASK) {
+	switch (regs->psr & PSR_MODE_MASK) {
 	case PSR_MODE_EL0t:
 		el = "EL0t";
 		break;
@@ -160,11 +160,11 @@ static void apple_rtkit_crashlog_dump_regs(struct apple_rtkit *rtk, u8 *bfr,
 
 	dev_warn(rtk->dev, "RTKit: Exception dump:");
 	dev_warn(rtk->dev, "  == Exception taken from %s ==", el);
-	dev_warn(rtk->dev, "  PSR    = 0x%llx", regs.psr);
-	dev_warn(rtk->dev, "  PC     = 0x%llx\n", regs.pc);
-	dev_warn(rtk->dev, "  ESR    = 0x%llx\n", regs.esr);
-	dev_warn(rtk->dev, "  FAR    = 0x%llx\n", regs.far);
-	dev_warn(rtk->dev, "  SP     = 0x%llx\n", regs.sp);
+	dev_warn(rtk->dev, "  PSR    = 0x%llx", regs->psr);
+	dev_warn(rtk->dev, "  PC     = 0x%llx\n", regs->pc);
+	dev_warn(rtk->dev, "  ESR    = 0x%llx\n", regs->esr);
+	dev_warn(rtk->dev, "  FAR    = 0x%llx\n", regs->far);
+	dev_warn(rtk->dev, "  SP     = 0x%llx\n", regs->sp);
 	dev_warn(rtk->dev, "\n");
 
 	for (i = 0; i < 31; i += 4) {
@@ -172,12 +172,12 @@ static void apple_rtkit_crashlog_dump_regs(struct apple_rtkit *rtk, u8 *bfr,
 			dev_warn(rtk->dev,
 					 "  x%02d-x%02d = %016llx %016llx %016llx %016llx\n",
 					 i, i + 3,
-					 regs.regs[i], regs.regs[i + 1],
-					 regs.regs[i + 2], regs.regs[i + 3]);
+					 regs->regs[i], regs->regs[i + 1],
+					 regs->regs[i + 2], regs->regs[i + 3]);
 		else
 			dev_warn(rtk->dev,
 					 "  x%02d-x%02d = %016llx %016llx %016llx\n", i, i + 3,
-					 regs.regs[i], regs.regs[i + 1], regs.regs[i + 2]);
+					 regs->regs[i], regs->regs[i + 1], regs->regs[i + 2]);
 	}
 
 	dev_warn(rtk->dev, "\n");
-- 
2.35.1