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Message-Id: <20201125193626.2266995-4-jim.cromie@gmail.com>
Date: Wed, 25 Nov 2020 12:36:22 -0700
From: Jim Cromie <jim.cromie@...il.com>
To: linux-mm@...ck.org
Cc: gregkh@...uxfoundation.org, linux@...musvillemoes.dk,
Jim Cromie <jim.cromie@...il.com>,
Jason Baron <jbaron@...mai.com>, linux-kernel@...r.kernel.org
Subject: [PATCH 3/7] dyndbg: add some code to see alignments of linkage data
To be able to use LSB-stealing (lsb as flag, mask b4 addressing), we
need to know that the alignments of existing data is never odd. So
add code to check the alignment of pointers in _dyndbg_callsites
section.
It turns out that all these fields point to a variety of odd
alignments in the deeper linkage data. We will need ALIGN(2) to allow
use of LSB to signal the EOT of differing-tail records.
[ 0.587654] dyndbg: 2014 entries. \
repeated entries: 1789 module 1667 file 809 func
[ 0.588653] dyndbg: mod aligns:
[ 0.589130] dyndbg: align 0 0: 107
[ 0.589653] dyndbg: align 0 1: 210
[ 0.590271] dyndbg: align 0 2: 234
[ 0.590652] dyndbg: align 0 3: 179
[ 0.591224] dyndbg: align 0 4: 358
[ 0.591652] dyndbg: align 0 5: 374
[ 0.592283] dyndbg: align 0 6: 231
[ 0.592653] dyndbg: align 0 7: 321
[ 0.593203] dyndbg: mod align totals: 2014
[ 0.593652] dyndbg: file aligns:
[ 0.594168] dyndbg: align 1 0: 569
[ 0.594652] dyndbg: align 1 1: 172
[ 0.595179] dyndbg: align 1 2: 263
[ 0.595652] dyndbg: align 1 3: 252
[ 0.596368] dyndbg: align 1 4: 200
[ 0.596652] dyndbg: align 1 5: 126
[ 0.597327] dyndbg: align 1 6: 177
[ 0.597669] dyndbg: align 1 7: 255
[ 0.598316] dyndbg: file align totals: 2014
[ 0.598652] dyndbg: func aligns:
[ 0.599214] dyndbg: align 2 0: 2006
[ 0.599652] dyndbg: align 2 1: 7
[ 0.600168] dyndbg: align 2 2: 0
[ 0.600648] dyndbg: align 2 3: 0
[ 0.600652] dyndbg: align 2 4: 0
[ 0.601105] dyndbg: align 2 5: 0
[ 0.601652] dyndbg: align 2 6: 0
[ 0.602203] dyndbg: align 2 7: 1
[ 0.602654] dyndbg: func align totals: 2014
[ 0.603431] dyndbg: format aligns:
[ 0.603658] dyndbg: align 3 0: 1053
[ 0.604429] dyndbg: align 3 1: 134
[ 0.604653] dyndbg: align 3 2: 161
[ 0.605181] dyndbg: align 3 3: 142
[ 0.605652] dyndbg: align 3 4: 137
[ 0.606250] dyndbg: align 3 5: 117
[ 0.606652] dyndbg: align 3 6: 124
[ 0.607183] dyndbg: align 3 7: 146
[ 0.608669] dyndbg: earlyprintk="serial,ttyS0,115200"
This means low order bits are unavailable for encoding extra info, as
is done in struct static_key.
Consider the last lines of /proc/dynamic_debug/control, here with
matching fields replaced by '^'. The pattern here is common head(s)
& differing tail(s).
init/main.c main run_init_process " %s\012" 1339
^ ^ ^ " with environment:\012" 1337
^ ^ ^ " %s\012" 1336
^ ^ ^ " with arguments:\012" 1334
^ ^ initcall_blacklisted "initcall %s blacklisted\012" 1123
^ ^ initcall_blacklist "blacklisting initcall %s\012" 1084
struct ddebug_callsite fields [mod, file, func, format] are 4-tuples;
each element points at different kinds/sources of linkage data
(&module->name, __FILE__, __FUNC__, format-strings).
callsite-tails are 4,3,2,1-tuples, with matching heads removed.
If we can force ALIGN(2) on all those linkage data sources, then we
can use +1 to mark the Beginning-Of-Tuple (or EOT), and so distinguish
amongst the N-tuples, and reconstruct each record by copying and
changing the previous record. Each new module block starts with a
4-tuple; the init/main example block above is a 4,1,1,1,2,2-tuple
sequence, using 11/24 of the space.
Signed-off-by: Jim Cromie <jim.cromie@...il.com>
---
lib/dynamic_debug.c | 27 ++++++++++++++++++++++++++-
1 file changed, 26 insertions(+), 1 deletion(-)
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 5980d44ff2f8..c84efb4e036b 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -1079,6 +1079,13 @@ static int __init dynamic_debug_init_control(void)
return 0;
}
+
+static __initdata int alignments[4][8];
+static void bump_ct(int i, const char *p)
+{
+ alignments[i][ (long)p & 7 ]++;
+}
+
static int __init dynamic_debug_init(void)
{
struct _ddebug *iter, *iter_start, *prev = NULL;
@@ -1087,7 +1094,9 @@ static int __init dynamic_debug_init(void)
int ret = 0;
int n = 0, entries = 0, modct = 0;
int modreps = 0, funcreps = 0, filereps = 0;
-
+ int i,k;
+ char *kind[] = { "mod","file","func","format" };
+
if (&__start___dyndbg == &__stop___dyndbg) {
if (IS_ENABLED(CONFIG_DYNAMIC_DEBUG)) {
pr_warn("_ddebug table is empty in a CONFIG_DYNAMIC_DEBUG build\n");
@@ -1111,6 +1120,12 @@ static int __init dynamic_debug_init(void)
prev++; /* one behind iter */
}
entries++;
+
+ bump_ct(0, iter->site->modname);
+ bump_ct(1, iter->site->filename);
+ bump_ct(2, iter->site->function);
+ bump_ct(3, iter->site->format);
+
if (strcmp(modname, iter->site->modname)) {
modct++;
ret = ddebug_add_module(iter_start, n, modname);
@@ -1135,6 +1150,16 @@ static int __init dynamic_debug_init(void)
vpr_info("%d entries. repeated entries: %d module %d file %d func\n",
entries, modreps, filereps, funcreps);
+ /* display alignment info on fields */
+ for (i=0; i<4; i++) {
+ k = 0;
+ vpr_info("%s aligns:\n", kind[i]);
+ for (n=0; n<8; n++) {
+ vpr_info(" align %d %d: %d\n", i, n, alignments[i][n]);
+ k += alignments[i][n];
+ }
+ vpr_info(" %s align totals: %d\n", kind[i], k);
+ }
/* apply ddebug_query boot param, dont unload tables on err */
if (ddebug_setup_string[0] != '\0') {
pr_warn("ddebug_query param name is deprecated, change it to dyndbg\n");
--
2.28.0
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