Commit 787983da authored by Gary Guo's avatar Gary Guo Committed by Miguel Ojeda
Browse files

vsprintf: add new `%pA` format specifier 



This patch adds a format specifier `%pA` to `vsprintf` which formats
a pointer as `core::fmt::Arguments`. Doing so allows us to directly
format to the internal buffer of `printf`, so we do not have to use
a temporary buffer on the stack to pre-assemble the message on
the Rust side.

This specifier is intended only to be used from Rust and not for C, so
`checkpatch.pl` is intentionally unchanged to catch any misuse.

Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Acked-by: default avatarPetr Mladek <pmladek@suse.com>
Reviewed-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Co-developed-by: default avatarAlex Gaynor <alex.gaynor@gmail.com>
Signed-off-by: default avatarAlex Gaynor <alex.gaynor@gmail.com>
Co-developed-by: default avatarWedson Almeida Filho <wedsonaf@google.com>
Signed-off-by: default avatarWedson Almeida Filho <wedsonaf@google.com>
Signed-off-by: default avatarGary Guo <gary@garyguo.net>
Co-developed-by: default avatarMiguel Ojeda <ojeda@kernel.org>
Signed-off-by: default avatarMiguel Ojeda <ojeda@kernel.org>
parent 8fcbf024

Documentation/core-api/printk-formats.rst

+10 −0
Original line number Diff line number Diff line
@@ -625,6 +625,16 @@ Examples:: 
	%p4cc	Y10  little-endian (0x20303159)

	%p4cc	NV12 big-endian (0xb231564e)



Rust

----



::



	%pA



Only intended to be used from Rust code to format ``core::fmt::Arguments``.

Do *not* use it from C.



Thanks

======

lib/vsprintf.c

+13 −0
Original line number Diff line number Diff line
@@ -2246,6 +2246,9 @@ int __init no_hash_pointers_enable(char *str) 
}

early_param("no_hash_pointers", no_hash_pointers_enable);



/* Used for Rust formatting ('%pA'). */

char *rust_fmt_argument(char *buf, char *end, void *ptr);



/*

 * Show a '%p' thing.  A kernel extension is that the '%p' is followed

 * by an extra set of alphanumeric characters that are extended format
@@ -2372,6 +2375,10 @@ early_param("no_hash_pointers", no_hash_pointers_enable); 
 *

 * Note: The default behaviour (unadorned %p) is to hash the address,

 * rendering it useful as a unique identifier.

 *

 * There is also a '%pA' format specifier, but it is only intended to be used

 * from Rust code to format core::fmt::Arguments. Do *not* use it from C.

 * See rust/kernel/print.rs for details.

 */

static noinline_for_stack

char *pointer(const char *fmt, char *buf, char *end, void *ptr,
@@ -2444,6 +2451,12 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr, 
		return device_node_string(buf, end, ptr, spec, fmt + 1);

	case 'f':

		return fwnode_string(buf, end, ptr, spec, fmt + 1);

	case 'A':

		if (!IS_ENABLED(CONFIG_RUST)) {

			WARN_ONCE(1, "Please remove %%pA from non-Rust code\n");

			return error_string(buf, end, "(%pA?)", spec);

		}

		return rust_fmt_argument(buf, end, ptr);

	case 'x':

		return pointer_string(buf, end, ptr, spec);

	case 'e':