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nptl: Remove COLORING_INCREMENT

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This patch removes the COLORING_INCREMENT define and usage on allocatestack.c.
It has not been used since 564cd8b67ec487f (glibc-2.3.3) by any architecture.
The idea is to simplify the code by removing obsolete code.

	* nptl/allocatestack.c [COLORING_INCREMENT] (nptl_ncreated): Remove.
	(allocate_stack): Remove COLORING_INCREMENT usage.
	* nptl/stack-aliasing.h (COLORING_INCREMENT). Likewise.
	* sysdeps/i386/i686/stack-aliasing.h (COLORING_INCREMENT): Likewise.
This commit is contained in:
Adhemerval Zanella 2017-01-30 18:07:32 -02:00
parent 2b7dc4c868
commit 37f8abad1c
4 changed files with 9 additions and 49 deletions
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7
ChangeLog
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@ -1,3 +1,10 @@
2016-02-06 Adhemerval Zanella <adhemerval.zanella@linaro.org>
* nptl/allocatestack.c [COLORING_INCREMENT] (nptl_ncreated): Remove.
(allocate_stack): Remove COLORING_INCREMENT usage.
* nptl/stack-aliasing.h (COLORING_INCREMENT). Likewise.
* sysdeps/i386/i686/stack-aliasing.h (COLORING_INCREMENT): Likewise.
2017-02-06 Joseph Myers <joseph@codesourcery.com>
* manual/libm-err-tab.pl (@all_functions): Change to

40
nptl/allocatestack.c
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@ -125,11 +125,6 @@ static uintptr_t in_flight_stack;
list_t __stack_user __attribute__ ((nocommon));
hidden_data_def (__stack_user)
#if COLORING_INCREMENT != 0
/* Number of threads created. */
static unsigned int nptl_ncreated;
#endif
/* Check whether the stack is still used or not. */
#define FREE_P(descr) ((descr)->tid <= 0)
@ -467,14 +462,6 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp,
const int prot = (PROT_READ | PROT_WRITE
| ((GL(dl_stack_flags) & PF_X) ? PROT_EXEC : 0));
#if COLORING_INCREMENT != 0
/* Add one more page for stack coloring. Don't do it for stacks
with 16 times pagesize or larger. This might just cause
unnecessary misalignment. */
if (size <= 16 * pagesize_m1)
size += pagesize_m1 + 1;
#endif
/* Adjust the stack size for alignment. */
size &= ~__static_tls_align_m1;
assert (size != 0);
@ -513,34 +500,11 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp,
So we can never get a null pointer back from mmap. */
assert (mem != NULL);
#if COLORING_INCREMENT != 0
/* Atomically increment NCREATED. */
unsigned int ncreated = atomic_increment_val (&nptl_ncreated);
/* We chose the offset for coloring by incrementing it for
every new thread by a fixed amount. The offset used
module the page size. Even if coloring would be better
relative to higher alignment values it makes no sense to
do it since the mmap() interface does not allow us to
specify any alignment for the returned memory block. */
size_t coloring = (ncreated * COLORING_INCREMENT) & pagesize_m1;
/* Make sure the coloring offsets does not disturb the alignment
of the TCB and static TLS block. */
if (__glibc_unlikely ((coloring & __static_tls_align_m1) != 0))
coloring = (((coloring + __static_tls_align_m1)
& ~(__static_tls_align_m1))
& ~pagesize_m1);
#else
/* Unless specified we do not make any adjustments. */
# define coloring 0
#endif
/* Place the thread descriptor at the end of the stack. */
#if TLS_TCB_AT_TP
pd = (struct pthread *) ((char *) mem + size - coloring) - 1;
pd = (struct pthread *) ((char *) mem + size) - 1;
#elif TLS_DTV_AT_TP
pd = (struct pthread *) ((((uintptr_t) mem + size - coloring
pd = (struct pthread *) ((((uintptr_t) mem + size
- __static_tls_size)
& ~__static_tls_align_m1)
- TLS_PRE_TCB_SIZE);

6
nptl/stack-aliasing.h
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@ -16,12 +16,6 @@
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
/* This is a number of bytes (less than a page) by which to "color" the
starting stack address of new threads. This number is multiplied by the
number of threads created so far and then truncated modulo page size,
to get a roughly even distribution of values for different threads. */
#define COLORING_INCREMENT 0
/* This is a number of bytes that is an alignment that should be avoided
when choosing the exact size of a new thread's stack. If the size
chosen is aligned to this, an extra page will be added to render the

5
sysdeps/i386/i686/stack-aliasing.h
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@ -16,11 +16,6 @@
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
/* It turns out that stack coloring is in general not good on P4s. Some
applications will benefit. We will probably have a configuration option
at some point. To enable coloring, set this to 128. */
#define COLORING_INCREMENT 0
/* What is useful is to avoid the 64k aliasing problem which reliably
happens if all stacks use sizes which are a multiple of 64k. Tell
the stack allocator to disturb this by allocation one more page if