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Subject[PATCH v2] earlycon: Fix __earlycon_table stride... again
Date
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@chromium.org>
---
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
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