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290 lines
11 KiB
290 lines
11 KiB
commit 0c7b002fac12dcb2f53ba83ee56bb3b5d2439447
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Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
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Date: Tue Jun 9 09:57:28 2020 +0100
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rtld: Add rtld.nns tunable for the number of supported namespaces
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TLS_STATIC_SURPLUS is 1664 bytes currently which is not enough to
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support DL_NNS (== 16) number of dynamic link namespaces, if we
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assume 192 bytes of TLS are reserved for libc use and 144 bytes
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are reserved for other system libraries that use IE TLS.
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A new tunable is introduced to control the number of supported
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namespaces and to adjust the surplus static TLS size as follows:
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surplus_tls = 192 * (rtld.nns-1) + 144 * rtld.nns + 512
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The default is rtld.nns == 4 and then the surplus TLS size is the
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same as before, so the behaviour is unchanged by default. If an
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application creates more namespaces than the rtld.nns setting
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allows, then it is not guaranteed to work, but the limit is not
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checked. So existing usage will continue to work, but in the
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future if an application creates more than 4 dynamic link
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namespaces then the tunable will need to be set.
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In this patch DL_NNS is a fixed value and provides a maximum to
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the rtld.nns setting.
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Static linking used fixed 2048 bytes surplus TLS, this is changed
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so the same contract is used as for dynamic linking. With static
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linking DL_NNS == 1 so rtld.nns tunable is forced to 1, so by
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default the surplus TLS is reduced to 144 + 512 = 656 bytes. This
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change is not expected to cause problems.
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Tested on aarch64-linux-gnu and x86_64-linux-gnu.
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Reviewed-by: Carlos O'Donell <carlos@redhat.com>
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Conflicts:
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elf/dl-tls.c
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(Different per-namespace TLS reservation defaults before
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this backport.)
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diff --git a/csu/libc-tls.c b/csu/libc-tls.c
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index 28a79441cde379f7..08ed2b988b58ac6c 100644
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--- a/csu/libc-tls.c
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+++ b/csu/libc-tls.c
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@@ -52,13 +52,16 @@ bool _dl_tls_dtv_gaps;
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struct dtv_slotinfo_list *_dl_tls_dtv_slotinfo_list;
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/* Number of modules in the static TLS block. */
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size_t _dl_tls_static_nelem;
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-/* Size of the static TLS block. Giving this initialized value
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- preallocates some surplus bytes in the static TLS area. */
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-size_t _dl_tls_static_size = 2048;
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+/* Size of the static TLS block. */
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+size_t _dl_tls_static_size;
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/* Size actually allocated in the static TLS block. */
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size_t _dl_tls_static_used;
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/* Alignment requirement of the static TLS block. */
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size_t _dl_tls_static_align;
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+/* Size of surplus space in the static TLS area for dynamically
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+ loaded modules with IE-model TLS or for TLSDESC optimization.
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+ See comments in elf/dl-tls.c where it is initialized. */
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+size_t _dl_tls_static_surplus;
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/* Generation counter for the dtv. */
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size_t _dl_tls_generation;
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@@ -87,10 +90,8 @@ init_slotinfo (void)
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static void
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init_static_tls (size_t memsz, size_t align)
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{
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- /* That is the size of the TLS memory for this object. The initialized
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- value of _dl_tls_static_size is provided by dl-open.c to request some
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- surplus that permits dynamic loading of modules with IE-model TLS. */
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- GL(dl_tls_static_size) = roundup (memsz + GL(dl_tls_static_size),
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+ /* That is the size of the TLS memory for this object. */
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+ GL(dl_tls_static_size) = roundup (memsz + GLRO(dl_tls_static_surplus),
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TLS_TCB_ALIGN);
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#if TLS_TCB_AT_TP
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GL(dl_tls_static_size) += TLS_TCB_SIZE;
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@@ -131,25 +132,24 @@ __libc_setup_tls (void)
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break;
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}
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+ /* Calculate the size of the static TLS surplus. */
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+ _dl_tls_static_surplus_init ();
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+
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/* We have to set up the TCB block which also (possibly) contains
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'errno'. Therefore we avoid 'malloc' which might touch 'errno'.
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Instead we use 'sbrk' which would only uses 'errno' if it fails.
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In this case we are right away out of memory and the user gets
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- what she/he deserves.
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-
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- The initialized value of _dl_tls_static_size is provided by dl-open.c
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- to request some surplus that permits dynamic loading of modules with
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- IE-model TLS. */
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+ what she/he deserves. */
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#if TLS_TCB_AT_TP
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/* Align the TCB offset to the maximum alignment, as
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_dl_allocate_tls_storage (in elf/dl-tls.c) does using __libc_memalign
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and dl_tls_static_align. */
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- tcb_offset = roundup (memsz + GL(dl_tls_static_size), max_align);
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+ tcb_offset = roundup (memsz + GLRO(dl_tls_static_surplus), max_align);
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tlsblock = __sbrk (tcb_offset + TLS_INIT_TCB_SIZE + max_align);
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#elif TLS_DTV_AT_TP
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tcb_offset = roundup (TLS_INIT_TCB_SIZE, align ?: 1);
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tlsblock = __sbrk (tcb_offset + memsz + max_align
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- + TLS_PRE_TCB_SIZE + GL(dl_tls_static_size));
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+ + TLS_PRE_TCB_SIZE + GLRO(dl_tls_static_surplus));
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tlsblock += TLS_PRE_TCB_SIZE;
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#else
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/* In case a model with a different layout for the TCB and DTV
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diff --git a/elf/dl-tls.c b/elf/dl-tls.c
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index a2def280b7096960..ef57a21391bb36fa 100644
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--- a/elf/dl-tls.c
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+++ b/elf/dl-tls.c
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@@ -29,10 +29,54 @@
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#include <dl-tls.h>
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#include <ldsodefs.h>
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-/* Amount of excess space to allocate in the static TLS area
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- to allow dynamic loading of modules defining IE-model TLS data. */
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-#define TLS_STATIC_SURPLUS 64 + DL_NNS * 100
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+#define TUNABLE_NAMESPACE rtld
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+#include <dl-tunables.h>
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+
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+/* Surplus static TLS, GLRO(dl_tls_static_surplus), is used for
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+
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+ - IE TLS in libc.so for all dlmopen namespaces except in the initial
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+ one where libc.so is not loaded dynamically but at startup time,
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+ - IE TLS in other libraries which may be dynamically loaded even in the
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+ initial namespace,
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+ - and optionally for optimizing dynamic TLS access.
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+
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+ The maximum number of namespaces is DL_NNS, but to support that many
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+ namespaces correctly the static TLS allocation should be significantly
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+ increased, which may cause problems with small thread stacks due to the
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+ way static TLS is accounted (bug 11787).
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+
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+ So there is a rtld.nns tunable limit on the number of supported namespaces
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+ that affects the size of the static TLS and by default it's small enough
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+ not to cause problems with existing applications. The limit is not
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+ enforced or checked: it is the user's responsibility to increase rtld.nns
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+ if more dlmopen namespaces are used. */
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+
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+/* Size of initial-exec TLS in libc.so. */
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+#define LIBC_IE_TLS 192
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+/* Size of initial-exec TLS in libraries other than libc.so.
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+ This should be large enough to cover runtime libraries of the
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+ compiler such as libgomp and libraries in libc other than libc.so. */
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+#define OTHER_IE_TLS 144
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+/* Size of additional surplus TLS, placeholder for TLS optimizations. */
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+#define OPT_SURPLUS_TLS 512
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+void
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+_dl_tls_static_surplus_init (void)
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+{
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+ size_t nns;
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+
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+#if HAVE_TUNABLES
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+ nns = TUNABLE_GET (nns, size_t, NULL);
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+#else
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+ /* Default values of the tunables. */
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+ nns = 4;
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+#endif
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+ if (nns > DL_NNS)
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+ nns = DL_NNS;
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+ GLRO(dl_tls_static_surplus) = ((nns - 1) * LIBC_IE_TLS
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+ + nns * OTHER_IE_TLS
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+ + OPT_SURPLUS_TLS);
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+}
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/* Out-of-memory handler. */
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static void
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@@ -218,7 +262,8 @@ _dl_determine_tlsoffset (void)
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}
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GL(dl_tls_static_used) = offset;
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- GL(dl_tls_static_size) = (roundup (offset + TLS_STATIC_SURPLUS, max_align)
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+ GL(dl_tls_static_size) = (roundup (offset + GLRO(dl_tls_static_surplus),
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+ max_align)
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+ TLS_TCB_SIZE);
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#elif TLS_DTV_AT_TP
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/* The TLS blocks start right after the TCB. */
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@@ -262,7 +307,7 @@ _dl_determine_tlsoffset (void)
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}
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GL(dl_tls_static_used) = offset;
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- GL(dl_tls_static_size) = roundup (offset + TLS_STATIC_SURPLUS,
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+ GL(dl_tls_static_size) = roundup (offset + GLRO(dl_tls_static_surplus),
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TLS_TCB_ALIGN);
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#else
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# error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
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diff --git a/elf/dl-tunables.list b/elf/dl-tunables.list
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index b7cc79f8bfe0a7c6..7337fb85062c91a7 100644
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--- a/elf/dl-tunables.list
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+++ b/elf/dl-tunables.list
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@@ -126,4 +126,13 @@ glibc {
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default: 3
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}
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}
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+
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+ rtld {
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+ nns {
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+ type: SIZE_T
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+ minval: 1
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+ maxval: 16
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+ default: 4
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+ }
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+ }
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}
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diff --git a/elf/rtld.c b/elf/rtld.c
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index 772aff5160359b7b..a440741f4c1b3c91 100644
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--- a/elf/rtld.c
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+++ b/elf/rtld.c
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@@ -776,6 +776,9 @@ init_tls (void)
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}
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assert (i == GL(dl_tls_max_dtv_idx));
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+ /* Calculate the size of the static TLS surplus. */
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+ _dl_tls_static_surplus_init ();
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+
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/* Compute the TLS offsets for the various blocks. */
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_dl_determine_tlsoffset ();
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diff --git a/manual/tunables.texi b/manual/tunables.texi
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index 55d5dfb14db4dfb8..e092b8e81a18d739 100644
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--- a/manual/tunables.texi
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+++ b/manual/tunables.texi
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@@ -31,6 +31,7 @@ their own namespace.
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@menu
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* Tunable names:: The structure of a tunable name
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* Memory Allocation Tunables:: Tunables in the memory allocation subsystem
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+* Dynamic Linking Tunables:: Tunables in the dynamic linking subsystem
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* Elision Tunables:: Tunables in elision subsystem
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* Hardware Capability Tunables:: Tunables that modify the hardware
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capabilities seen by @theglibc{}
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@@ -225,6 +226,26 @@ pointer, so add 4 on 32-bit systems or 8 on 64-bit systems to the size
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passed to @code{malloc} for the largest bin size to enable.
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@end deftp
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+@node Dynamic Linking Tunables
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+@section Dynamic Linking Tunables
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+@cindex dynamic linking tunables
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+@cindex rtld tunables
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+
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+@deftp {Tunable namespace} glibc.rtld
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+Dynamic linker behavior can be modified by setting the
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+following tunables in the @code{rtld} namespace:
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+@end deftp
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+
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+@deftp Tunable glibc.rtld.nns
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+Sets the number of supported dynamic link namespaces (see @code{dlmopen}).
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+Currently this limit can be set between 1 and 16 inclusive, the default is 4.
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+Each link namespace consumes some memory in all thread, and thus raising the
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+limit will increase the amount of memory each thread uses. Raising the limit
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+is useful when your application uses more than 4 dynamic linker audit modules
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+e.g. @env{LD_AUDIT}, or will use more than 4 dynamic link namespaces as created
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+by @code{dlmopen} with an lmid argument of @code{LM_ID_NEWLM}.
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+@end deftp
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+
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@node Elision Tunables
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@section Elision Tunables
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@cindex elision tunables
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diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
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index ccec08929e4ad4e7..e54105848c3cb7d1 100644
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--- a/sysdeps/generic/ldsodefs.h
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+++ b/sysdeps/generic/ldsodefs.h
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@@ -582,6 +582,11 @@ struct rtld_global_ro
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binaries, don't honor for PIEs). */
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EXTERN ElfW(Addr) _dl_use_load_bias;
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+ /* Size of surplus space in the static TLS area for dynamically
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+ loaded modules with IE-model TLS or for TLSDESC optimization.
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+ See comments in elf/dl-tls.c where it is initialized. */
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+ EXTERN size_t _dl_tls_static_surplus;
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+
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/* Name of the shared object to be profiled (if any). */
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EXTERN const char *_dl_profile;
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/* Filename of the output file. */
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@@ -1099,6 +1104,9 @@ extern size_t _dl_count_modids (void) attribute_hidden;
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/* Calculate offset of the TLS blocks in the static TLS block. */
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extern void _dl_determine_tlsoffset (void) attribute_hidden;
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+/* Calculate the size of the static TLS surplus. */
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+void _dl_tls_static_surplus_init (void) attribute_hidden;
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+
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#ifndef SHARED
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/* Set up the TCB for statically linked applications. This is called
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early during startup because we always use TLS (for errno and the
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