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vsprintf: add new %pA format specifier

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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: Kees Cook <keescook@chromium.org>
Acked-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Co-developed-by: Alex Gaynor <alex.gaynor@gmail.com>
Signed-off-by: Alex Gaynor <alex.gaynor@gmail.com>
Co-developed-by: Wedson Almeida Filho <wedsonaf@google.com>
Signed-off-by: Wedson Almeida Filho <wedsonaf@google.com>
Signed-off-by: Gary Guo <gary@garyguo.net>
Co-developed-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
This commit is contained in:
Gary Guo 2021-07-03 17:38:57 +02:00 committed by Miguel Ojeda
parent 8fcbf02492
commit 787983da77
2 changed files with 23 additions and 0 deletions
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10
Documentation/core-api/printk-formats.rst
View file

@ -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
======

13
lib/vsprintf.c
View file

@ -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':