Le 03/03/2021 à 18:46, Will Deacon a écrit :

On Wed, Mar 03, 2021 at 06:38:16PM +0100, Christophe Leroy wrote:

quoted

Le 03/03/2021 à 18:28, Will Deacon a écrit :

quoted

On Tue, Mar 02, 2021 at 05:25:17PM +0000, Christophe Leroy wrote:

quoted

This code provides architectures with a way to build command line
based on what is built in the kernel and what is handed over by the
bootloader, based on selected compile-time options.

Signed-off-by: Christophe Leroy <redacted>
---
   include/linux/cmdline.h | 62 +++++++++++++++++++++++++++++++++++++++++
   1 file changed, 62 insertions(+)
   create mode 100644 include/linux/cmdline.h

diff --git a/include/linux/cmdline.h b/include/linux/cmdline.h
new file mode 100644
index 000000000000..ae3610bb0ee2
--- /dev/null
+++ b/include/linux/cmdline.h

@@ -0,0 +1,62 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_CMDLINE_H
+#define _LINUX_CMDLINE_H
+
+static __always_inline size_t cmdline_strlen(const char *s)
+{
+	const char *sc;
+
+	for (sc = s; *sc != '\0'; ++sc)
+		; /* nothing */
+	return sc - s;
+}
+
+static __always_inline size_t cmdline_strlcat(char *dest, const char *src, size_t count)
+{
+	size_t dsize = cmdline_strlen(dest);
+	size_t len = cmdline_strlen(src);
+	size_t res = dsize + len;
+
+	/* This would be a bug */
+	if (dsize >= count)
+		return count;
+
+	dest += dsize;
+	count -= dsize;
+	if (len >= count)
+		len = count - 1;
+	memcpy(dest, src, len);
+	dest[len] = 0;
+	return res;
+}

Why are these needed instead of using strlen and strlcat directly?

Because on powerpc (at least), it will be used in prom_init, it is very
early in the boot and KASAN shadow memory is not set up yet so calling
generic string functions would crash the board.

Hmm. We deliberately setup a _really_ early shadow on arm64 for this, can
you not do something similar? Failing that, I think it would be better to
offer the option for an arch to implement cmdline_*, but have then point to
the normal library routines by default.

I don't think it is possible to setup an earlier early shadow.

At the point we are in prom_init, the code is not yet relocated at the address it was linked for, 
and it is running with the MMU set by the bootloader, I can't imagine being able to setup MMU 
entries for the early shadow KASAN yet without breaking everything.

Is it really worth trying to point to the normal library routines by default ? It is really only a 
few lines of code hence only not many bytes, and anyway they are in __init section so they get 
discarded at the end.

quoted

quoted

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+/*
+ * This function will append a builtin command line to the command
+ * line provided by the bootloader. Kconfig options can be used to alter
+ * the behavior of this builtin command line.
+ * @dest: The destination of the final appended/prepended string.
+ * @src: The starting string or NULL if there isn't one. Must not equal dest.
+ * @length: the length of dest buffer.
+ */
+static __always_inline void cmdline_build(char *dest, const char *src, size_t length)
+{
+	if (length <= 0)
+		return;
+
+	dest[0] = 0;
+
+#ifdef CONFIG_CMDLINE
+	if (IS_ENABLED(CONFIG_CMDLINE_FORCE) || !src || !src[0]) {
+		cmdline_strlcat(dest, CONFIG_CMDLINE, length);
+		return;
+	}
+#endif

CONFIG_CMDLINE_FORCE implies CONFIG_CMDLINE, and even if it didn't,
CONFIG_CMDLINE is at worst an empty string. Can you drop the #ifdef?

Ah yes, since cbe46bd4f510 ("powerpc: remove CONFIG_CMDLINE #ifdef mess") it
is feasible. I can change that now.

quoted

quoted

+	if (dest != src)
+		cmdline_strlcat(dest, src, length);
+#ifdef CONFIG_CMDLINE
+	if (IS_ENABLED(CONFIG_CMDLINE_EXTEND) && sizeof(CONFIG_CMDLINE) > 1)
+		cmdline_strlcat(dest, " " CONFIG_CMDLINE, length);
+#endif

Likewise, but also I'm not sure why the sizeof() is required.

It is to avoid adding a white space at the end of the command line when
CONFIG_CMDLINE is empty. But maybe it doesn't matter ?

If CONFIG_CMDLINE is empty, I don't think you can select
CONFIG_CMDLINE_EXTEND (but even if you could, I don't think it matters).

Ok I'll simplify that when I re-spin.

Christophe