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[2a02:3100:b027:cd01:554a:ffde:5279:f351]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c24966f6b48sm1006377166b.33.2026.08.23.18.47.21 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Sun, 23 Aug 2026 18:47:22 -0700 (PDT) From: Karl Mehltretter To: Miquel Raynal , Richard Weinberger , Vignesh Raghavendra Cc: Karl Mehltretter , Andy Shevchenko , David Laight , Lukas Wunner , linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org Subject: [PATCH] mtd: cfi_cmdset_0001: shrink do_write_buffer() stack frame Date: Mon, 24 Aug 2026 03:47:03 +0200 Message-Id: <20260824014703.56502-1-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit arm32 allmodconfig fails to build with gcc: drivers/mtd/chips/cfi_cmdset_0001.c:1883:1: error: the frame size of 1296 bytes is larger than 1280 bytes [-Werror=frame-larger-than=] With MTD_MAP_BANK_WIDTH_32 a map_word is 32 bytes, and with KASAN_STACK every temporary gets its own redzoned slot. do_write_buffer() builds a map_word for each of the twelve commands it issues, and those temporaries dominate its frame. Issue the commands through a small noinline helper that takes the command as a plain value and builds the map_word in its own frame. The sequence of reads and writes to the chip is unchanged. The helper must not be inlined, and reusing one map_word local is not enough: clang cannot assume the callee does not observe the local, so it still returns each CMD() into a per-call-site temporary, and the frame grows (1760 -> 1824 bytes in cfi_intelext_writev(), into which clang inlines do_write_buffer()). Frame sizes with MTD_MAP_BANK_WIDTH_32 and KASAN_STACK: gcc 15.2 do_write_buffer() 1296 -> 520 clang 21 cfi_intelext_writev() 1760 -> 896 The helper itself takes 168 (gcc) / 160 (clang) bytes. Reported-by: Andy Shevchenko Closes: https://lore.kernel.org/all/20260408211407.2295175-1-andriy.shevchenko@linux.intel.com/ Suggested-by: Miquel Raynal Link: https://lore.kernel.org/all/87ik9cfm6g.fsf@bootlin.com/ Assisted-by: LLM Signed-off-by: Karl Mehltretter --- drivers/mtd/chips/cfi_cmdset_0001.c | 42 ++++++++++++++++++----------- 1 file changed, 26 insertions(+), 16 deletions(-) diff --git a/drivers/mtd/chips/cfi_cmdset_0001.c b/drivers/mtd/chips/cfi_cmdset_0001.c index b73596a8e021..a7c77c4e76ae 100644 --- a/drivers/mtd/chips/cfi_cmdset_0001.c +++ b/drivers/mtd/chips/cfi_cmdset_0001.c @@ -1716,12 +1716,24 @@ static int cfi_intelext_write_words (struct mtd_info *mtd, loff_t to , size_t le } +/* + * Keep noinline: inlined, the map_word temporaries put do_write_buffer() over + * the frame-size limit with MTD_MAP_BANK_WIDTH_32 and KASAN_STACK. + */ +static noinline void __xipram cfi_write_cmd(struct map_info *map, + unsigned long cmd, unsigned long adr) +{ + struct cfi_private *cfi = map->fldrv_priv; + + map_write(map, CMD(cmd), adr); +} + static int __xipram do_write_buffer(struct map_info *map, struct flchip *chip, unsigned long adr, const struct kvec **pvec, unsigned long *pvec_seek, int len) { struct cfi_private *cfi = map->fldrv_priv; - map_word status, write_cmd, datum; + map_word status, datum; unsigned long cmd_adr; int ret, wbufsize, word_gap, words; const struct kvec *vec; @@ -1740,9 +1752,6 @@ static int __xipram do_write_buffer(struct map_info *map, struct flchip *chip, if (is_LH28F640BF(cfi)) cmd_adr = adr; - /* Let's determine this according to the interleave only once */ - write_cmd = (cfi->cfiq->P_ID != P_ID_INTEL_PERFORMANCE) ? CMD(0xe8) : CMD(0xe9); - mutex_lock(&chip->mutex); ret = get_chip(map, chip, cmd_adr, FL_WRITING); if (ret) { @@ -1759,7 +1768,7 @@ static int __xipram do_write_buffer(struct map_info *map, struct flchip *chip, So we must check here and reset those bits if they're set. Otherwise we're just pissing in the wind */ if (chip->state != FL_STATUS) { - map_write(map, CMD(0x70), cmd_adr); + cfi_write_cmd(map, 0x70, cmd_adr); chip->state = FL_STATUS; } status = map_read(map, cmd_adr); @@ -1767,21 +1776,22 @@ static int __xipram do_write_buffer(struct map_info *map, struct flchip *chip, xip_enable(map, chip, cmd_adr); printk(KERN_WARNING "SR.4 or SR.5 bits set in buffer write (status %lx). Clearing.\n", status.x[0]); xip_disable(map, chip, cmd_adr); - map_write(map, CMD(0x50), cmd_adr); - map_write(map, CMD(0x70), cmd_adr); + cfi_write_cmd(map, 0x50, cmd_adr); + cfi_write_cmd(map, 0x70, cmd_adr); } chip->state = FL_WRITING_TO_BUFFER; - map_write(map, write_cmd, cmd_adr); + cfi_write_cmd(map, (cfi->cfiq->P_ID != P_ID_INTEL_PERFORMANCE) ? 0xe8 : 0xe9, + cmd_adr); ret = WAIT_TIMEOUT(map, chip, cmd_adr, 0, 0); if (ret) { /* Argh. Not ready for write to buffer */ map_word Xstatus = map_read(map, cmd_adr); - map_write(map, CMD(0x70), cmd_adr); + cfi_write_cmd(map, 0x70, cmd_adr); chip->state = FL_STATUS; status = map_read(map, cmd_adr); - map_write(map, CMD(0x50), cmd_adr); - map_write(map, CMD(0x70), cmd_adr); + cfi_write_cmd(map, 0x50, cmd_adr); + cfi_write_cmd(map, 0x70, cmd_adr); xip_enable(map, chip, cmd_adr); printk(KERN_ERR "%s: Chip not ready for buffer write. Xstatus = %lx, status = %lx\n", map->name, Xstatus.x[0], status.x[0]); @@ -1800,7 +1810,7 @@ static int __xipram do_write_buffer(struct map_info *map, struct flchip *chip, } /* Write length of data to come */ - map_write(map, CMD(words), cmd_adr ); + cfi_write_cmd(map, words, cmd_adr); /* Write data */ vec = *pvec; @@ -1837,7 +1847,7 @@ static int __xipram do_write_buffer(struct map_info *map, struct flchip *chip, *pvec_seek = vec_seek; /* GO GO GO */ - map_write(map, CMD(0xd0), cmd_adr); + cfi_write_cmd(map, 0xd0, cmd_adr); chip->state = FL_WRITING; ret = INVAL_CACHE_AND_WAIT(map, chip, cmd_adr, @@ -1845,7 +1855,7 @@ static int __xipram do_write_buffer(struct map_info *map, struct flchip *chip, chip->buffer_write_time, chip->buffer_write_time_max); if (ret) { - map_write(map, CMD(0x70), cmd_adr); + cfi_write_cmd(map, 0x70, cmd_adr); chip->state = FL_STATUS; xip_enable(map, chip, cmd_adr); printk(KERN_ERR "%s: buffer write error (status timeout)\n", map->name); @@ -1858,8 +1868,8 @@ static int __xipram do_write_buffer(struct map_info *map, struct flchip *chip, unsigned long chipstatus = MERGESTATUS(status); /* reset status */ - map_write(map, CMD(0x50), cmd_adr); - map_write(map, CMD(0x70), cmd_adr); + cfi_write_cmd(map, 0x50, cmd_adr); + cfi_write_cmd(map, 0x70, cmd_adr); xip_enable(map, chip, cmd_adr); if (chipstatus & 0x02) { -- 2.39.5 (Apple Git-154)