linux-kernel - [PATCH v5 1/4] parisc: Inline a type punning version of get_unaligned

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Message-ID: <20251016205126.2882625-2-irogers@google.com>
Date: Thu, 16 Oct 2025 13:51:23 -0700
From: Ian Rogers <irogers@...gle.com>
To: "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>, Helge Deller <deller@....de>, 
	Andy Lutomirski <luto@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, 
	Vincenzo Frascino <vincenzo.frascino@....com>, Ian Rogers <irogers@...gle.com>, 
	Arnaldo Carvalho de Melo <acme@...hat.com>, linux-parisc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Eric Biggers <ebiggers@...gle.com>, 
	Al Viro <viro@...iv.linux.org.uk>, Christophe Leroy <christophe.leroy@...roup.eu>, 
	"Jason A. Donenfeld" <Jason@...c4.com>
Subject: [PATCH v5 1/4] parisc: Inline a type punning version of get_unaligned_le32

Reading the byte/char output_len with get_unaligned_le32 can trigger
compiler warnings due to the size read. Avoid these warnings by using
type punning. This avoids issues when switching get_unaligned_t to
__builtin_memcpy.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 arch/parisc/boot/compressed/misc.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/parisc/boot/compressed/misc.c b/arch/parisc/boot/compressed/misc.c
index 9c83bd06ef15..111f267230a1 100644
--- a/arch/parisc/boot/compressed/misc.c
+++ b/arch/parisc/boot/compressed/misc.c
@@ -278,6 +278,19 @@ static void parse_elf(void *output)
 	free(phdrs);
 }
 
+/*
+ * The regular get_unaligned_le32 uses __builtin_memcpy which can trigger
+ * warnings when reading a byte/char output_len as an integer, as the size of a
+ * char is less than that of an integer. Use type punning and the packed
+ * attribute, which requires -fno-strict-aliasing, to work around the problem.
+ */
+static u32 punned_get_unaligned_le32(const void *p)
+{
+	const struct { __le32 x; } __packed * __get_pptr = p;
+
+	return le32_to_cpu(__get_pptr->x);
+}
+
 asmlinkage unsigned long __visible decompress_kernel(unsigned int started_wide,
 		unsigned int command_line,
 		const unsigned int rd_start,
@@ -309,7 +322,7 @@ asmlinkage unsigned long __visible decompress_kernel(unsigned int started_wide,
 	 * leave 2 MB for the stack.
 	 */
 	vmlinux_addr = (unsigned long) &_ebss + 2*1024*1024;
-	vmlinux_len = get_unaligned_le32(&output_len);
+	vmlinux_len = punned_get_unaligned_le32(&output_len);
 	output = (char *) vmlinux_addr;
 
 	/*
-- 
2.51.0.858.gf9c4a03a3a-goog