lkml.org 
[lkml]   [2018]   [Mar]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v2 2/2] earlycon: Use a pointer table to fix __earlycon_table stride
Date
Commit 99492c39f39f ("earlycon: Fix __earlycon_table stride") tried to fix
__earlycon_table stride by forcing the earlycon_id struct alignment to 32
and asking the linker to 32-byte align the __earlycon_table symbol. This
fix was based on commit 07fca0e57fca92 ("tracing: Properly align linker
defined symbols") which tried a similar fix for the tracing subsystem.

However, this fix doesn't quite work because there is no guarantee that
gcc will place structures packed into an array format. In fact, gcc 4.9
chooses to 64-byte align these structs by inserting additional padding
between the entries because it has no clue that they are supposed to be in
an array. If we are unlucky, the linker will assign symbol
"__earlycon_table" to a 32-byte aligned address which does not correpsond
to the 64-byte alignbed contents of section "__earlycon_table".

To address this same problem, the fix to the tracing system was
subsequently re-implemented using a more robust table of pointers approach
by commits:
3d56e331b653 ("tracing: Replace syscall_meta_data struct array with pointer array")
654986462939 ("tracepoints: Fix section alignment using pointer array")
e4a9ea5ee7c8 ("tracing: Replace trace_event struct array with pointer array")

Let's use this same "array of pointers to structs" approach for
EARLYCON_TABLE.

Fixes: 99492c39f39f ("earlycon: Fix __earlycon_table stride")
Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
Suggested-by: Aaron Durbin <adurbin@chromium.org>
---
Changes since v1:
* added Suggested-by and Fixes, and reworded the commit message per Randy.

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
\
 
 \ /
  Last update: 2018-03-20 18:58    [W:0.091 / U:27.424 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site