Re: [PATCH v2] earlycon: Fix __earlycon_table stride... again

From: Daniel Kurtz
Date: Wed Mar 14 2018 - 21:58:01 EST

On Wed, Mar 14, 2018 at 7:48 PM Daniel Kurtz <djkurtz@xxxxxxxxxxxx> wrote:

> Commit 470ca0de69fe ("serial: earlycon: Enable earlycon without command
> line param") added EARLYCON_TABLE().

> Commit 99492c39f39f ("earlycon: Fix __earlycon_table stride") referenced
> commit 07fca0e57fca92 ("tracing: Properly align linker defined symbols")
> and tried to fix EARLYCON_TABLE() using __aligned(32).

> However, the fix copied just works around compiler behavior. In fact, it
> was subsequently re-implemented for tracing using a table of pointers in
> commit 3d56e331b653 ("tracing: Replace syscall_meta_data struct array with
> pointer array"), commit 654986462939 ("tracepoints: Fix section alignment
> using pointer array") and commit e4a9ea5ee7c8 ("tracing: Replace
> trace_event struct array with pointer array").

> Let's do the same "array of pointers to structs" approach for
> EARLYCON_TABLE.

> Signed-off-by: Daniel Kurtz <djkurtz@xxxxxxxxxxxx>

Oops, I forgot to add:

Suggested-by: Aaron Durbin <adurbin@xxxxxxxxxxxx>

> ---
> Changes since v1:
> * Change __earlycon_table to an array of pointers.

> Note: I do not have a convenient system to test the of/fdt.c part of this
> patch, so would apreciate help verifying it. Thanks!

> drivers/of/fdt.c | 7 +++++--
> drivers/tty/serial/earlycon.c | 6 ++++--
> include/asm-generic/vmlinux.lds.h | 2 +-
> include/linux/serial_core.h | 21 ++++++++++++++-------
> 4 files changed, 24 insertions(+), 12 deletions(-)

> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> index 84aa9d676375..6da20b9688f7 100644
> --- a/drivers/of/fdt.c
> +++ b/drivers/of/fdt.c
> @@ -942,7 +942,7 @@ int __init early_init_dt_scan_chosen_stdout(void)
> int offset;
> const char *p, *q, *options = NULL;
> int l;
> - const struct earlycon_id *match;
> + const struct earlycon_id **p_match;
> const void *fdt = initial_boot_params;

> offset = fdt_path_offset(fdt, "/chosen");
> @@ -969,7 +969,10 @@ int __init early_init_dt_scan_chosen_stdout(void)
> return 0;
> }

> - for (match = __earlycon_table; match < __earlycon_table_end;
match++) {
> + for (p_match = __earlycon_table; p_match < __earlycon_table_end;
> + p_match++) {
> + const struct earlycon_id *match = *p_match;
> +
> if (!match->compatible[0])
> continue;

> diff --git a/drivers/tty/serial/earlycon.c b/drivers/tty/serial/earlycon.c
> index a24278380fec..22683393a0f2 100644
> --- a/drivers/tty/serial/earlycon.c
> +++ b/drivers/tty/serial/earlycon.c
> @@ -169,7 +169,7 @@ static int __init register_earlycon(char *buf, const
struct earlycon_id *match)
> */
> int __init setup_earlycon(char *buf)
> {
> - const struct earlycon_id *match;
> + const struct earlycon_id **p_match;

> if (!buf || !buf[0])
> return -EINVAL;
> @@ -177,7 +177,9 @@ int __init setup_earlycon(char *buf)
> if (early_con.flags & CON_ENABLED)
> return -EALREADY;

> - for (match = __earlycon_table; match < __earlycon_table_end;
match++) {
> + for (p_match = __earlycon_table; p_match < __earlycon_table_end;
> + p_match++) {
> + const struct earlycon_id *match = *p_match;
> size_t len = strlen(match->name);

> if (strncmp(buf, match->name, len))
> diff --git a/include/asm-generic/vmlinux.lds.h
b/include/asm-generic/vmlinux.lds.h
> index 1ab0e520d6fc..e17de55c2542 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -179,7 +179,7 @@
> #endif

> #ifdef CONFIG_SERIAL_EARLYCON
> -#define EARLYCON_TABLE() STRUCT_ALIGN(); \
> +#define EARLYCON_TABLE() . = ALIGN(8); \
> VMLINUX_SYMBOL(__earlycon_table) = .; \
> KEEP(*(__earlycon_table)) \
> VMLINUX_SYMBOL(__earlycon_table_end) = .;
> diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
> index b32df49a3bd5..93b7add47087 100644
> --- a/include/linux/serial_core.h
> +++ b/include/linux/serial_core.h
> @@ -351,10 +351,10 @@ struct earlycon_id {
> char name[16];
> char compatible[128];
> int (*setup)(struct earlycon_device *, const char *options);
> -} __aligned(32);
> +};

> -extern const struct earlycon_id __earlycon_table[];
> -extern const struct earlycon_id __earlycon_table_end[];
> +extern const struct earlycon_id *__earlycon_table[];
> +extern const struct earlycon_id *__earlycon_table_end[];

> #if defined(CONFIG_SERIAL_EARLYCON) && !defined(MODULE)
> #define EARLYCON_USED_OR_UNUSED __used
> @@ -362,12 +362,19 @@ extern const struct earlycon_id
__earlycon_table_end[];
> #define EARLYCON_USED_OR_UNUSED __maybe_unused
> #endif

> -#define OF_EARLYCON_DECLARE(_name, compat, fn) \
> - static const struct earlycon_id __UNIQUE_ID(__earlycon_##_name) \
> - EARLYCON_USED_OR_UNUSED __section(__earlycon_table) \
> +#define _OF_EARLYCON_DECLARE(_name, compat, fn, unique_id) \
> + static const struct earlycon_id unique_id \
> + EARLYCON_USED_OR_UNUSED __initdata \
> = { .name = __stringify(_name), \
> .compatible = compat, \
> - .setup = fn }
> + .setup = fn }; \
> + static const struct earlycon_id EARLYCON_USED_OR_UNUSED \
> + __section(__earlycon_table) \
> + * const __PASTE(__p, unique_id) = &unique_id
> +
> +#define OF_EARLYCON_DECLARE(_name, compat, fn) \
> + _OF_EARLYCON_DECLARE(_name, compat, fn, \
> + __UNIQUE_ID(__earlycon_##_name))

> #define EARLYCON_DECLARE(_name, fn) OF_EARLYCON_DECLARE(_name, "", fn)

> --
> 2.16.2.804.g6dcf76e118-goog