From ffee86d17b463d4e2bcc1070dc1d03dc88870bc4 Mon Sep 17 00:00:00 2001 From: Hector Martin Date: Tue, 8 Apr 2025 12:17:57 +0530 Subject: [PATCH 1/2] lib/vsprintf: Add support for generic FourCCs by extending %p4cc %p4cc is designed for DRM/V4L2 FourCCs with their specific quirks, but it's useful to be able to print generic 4-character codes formatted as an integer. Extend it to add format specifiers for printing generic 32-bit FourCCs with various endian semantics: %p4ch Host byte order %p4cn Network byte order %p4cl Little-endian %p4cb Big-endian The endianness determines how bytes are interpreted as a u32, and the FourCC is then always printed MSByte-first (this is the opposite of V4L/DRM FourCCs). This covers most practical cases, e.g. %p4cn would allow printing LSByte-first FourCCs stored in host endian order (other than the hex form being in character order, not the integer value). Acked-by: Rasmus Villemoes Reviewed-by: Andy Shevchenko Reviewed-by: Petr Mladek Tested-by: Petr Mladek Signed-off-by: Hector Martin Signed-off-by: Aditya Garg Reviewed-by: Kees Cook --- Documentation/core-api/printk-formats.rst | 32 ++++++++++++++++++ lib/vsprintf.c | 40 +++++++++++++++++++---- scripts/checkpatch.pl | 2 +- 3 files changed, 67 insertions(+), 7 deletions(-) diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst index 14e093da3..99df8d175 100644 --- a/Documentation/core-api/printk-formats.rst +++ b/Documentation/core-api/printk-formats.rst @@ -630,6 +630,38 @@ Examples:: %p4cc Y10 little-endian (0x20303159) %p4cc NV12 big-endian (0xb231564e) +Generic FourCC code +------------------- + +:: + %p4c[h[R]lb] gP00 (0x67503030) + +Print a generic FourCC code, as both ASCII characters and its numerical +value as hexadecimal. + +The generic FourCC code is always printed in the big-endian format, +the most significant byte first. This is the opposite of V4L/DRM FourCCs. + +The additional ``h``, ``hR``, ``l``, and ``b`` specifiers define what +endianness is used to load the stored bytes. The data might be interpreted +using the host, reversed host byte order, little-endian, or big-endian. + +Passed by reference. + +Examples for a little-endian machine, given &(u32)0x67503030:: + + %p4ch gP00 (0x67503030) + %p4chR 00Pg (0x30305067) + %p4cl gP00 (0x67503030) + %p4cb 00Pg (0x30305067) + +Examples for a big-endian machine, given &(u32)0x67503030:: + + %p4ch gP00 (0x67503030) + %p4chR 00Pg (0x30305067) + %p4cl 00Pg (0x30305067) + %p4cb gP00 (0x67503030) + Rust ---- diff --git a/lib/vsprintf.c b/lib/vsprintf.c index c5e2ec930..af0fd89cb 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -1760,27 +1760,49 @@ char *fourcc_string(char *buf, char *end, const u32 *fourcc, char output[sizeof("0123 little-endian (0x01234567)")]; char *p = output; unsigned int i; + bool pixel_fmt = false; u32 orig, val; - if (fmt[1] != 'c' || fmt[2] != 'c') + if (fmt[1] != 'c') return error_string(buf, end, "(%p4?)", spec); if (check_pointer(&buf, end, fourcc, spec)) return buf; orig = get_unaligned(fourcc); - val = orig & ~BIT(31); + switch (fmt[2]) { + case 'h': + if (fmt[3] == 'R') + orig = swab32(orig); + break; + case 'l': + orig = (__force u32)cpu_to_le32(orig); + break; + case 'b': + orig = (__force u32)cpu_to_be32(orig); + break; + case 'c': + /* Pixel formats are printed LSB-first */ + pixel_fmt = true; + break; + default: + return error_string(buf, end, "(%p4?)", spec); + } + + val = pixel_fmt ? swab32(orig & ~BIT(31)) : orig; for (i = 0; i < sizeof(u32); i++) { - unsigned char c = val >> (i * 8); + unsigned char c = val >> ((3 - i) * 8); /* Print non-control ASCII characters as-is, dot otherwise */ *p++ = isascii(c) && isprint(c) ? c : '.'; } - *p++ = ' '; - strcpy(p, orig & BIT(31) ? "big-endian" : "little-endian"); - p += strlen(p); + if (pixel_fmt) { + *p++ = ' '; + strcpy(p, orig & BIT(31) ? "big-endian" : "little-endian"); + p += strlen(p); + } *p++ = ' '; *p++ = '('; @@ -2334,6 +2356,12 @@ char *rust_fmt_argument(char *buf, char *end, void *ptr); * read the documentation (path below) first. * - 'NF' For a netdev_features_t * - '4cc' V4L2 or DRM FourCC code, with endianness and raw numerical value. + * - '4c[h[R]lb]' For generic FourCC code with raw numerical value. Both are + * displayed in the big-endian format. This is the opposite of V4L2 or + * DRM FourCCs. + * The additional specifiers define what endianness is used to load + * the stored bytes. The data might be interpreted using the host, + * reversed host byte order, little-endian, or big-endian. * - 'h[CDN]' For a variable-length buffer, it prints it as a hex string with * a certain separator (' ' by default): * C colon diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl index b03d526e4..e6d854f56 100755 --- a/scripts/checkpatch.pl +++ b/scripts/checkpatch.pl @@ -6912,7 +6912,7 @@ sub process { ($extension eq "f" && defined $qualifier && $qualifier !~ /^w/) || ($extension eq "4" && - defined $qualifier && $qualifier !~ /^cc/)) { + defined $qualifier && $qualifier !~ /^c[hnlbc]/)) { $bad_specifier = $specifier; last; } -- 2.49.0