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libs/libc/tls/Kconfig: Add CONFIG_TLS_ALIGNED

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CONFIG_TLS_ALIGNED will select the (legacy) aligned stack implementation of TLS.  If CONFIG_TLS_ALIGNED is not defined, then the new, implementation of TLS using an unaligned stack will be enabled.
This commit is contained in:
Gregory Nutt 2020-05-05 07:28:04 -06:00 committed by Abdelatif Guettouche
parent 8d763d37ab
commit b1071cca00
1 changed files with 26 additions and 6 deletions
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32
libs/libc/tls/Kconfig
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@ -21,17 +21,37 @@ config TLS
if TLS
config TLS_ALIGNED
bool "Require stack alignment"
default y if BUILD_KERNEL
default n if !BUILD_KERNEL
---help---
Aligned TLS works by fetch thread information from the beginning
of the stack memory allocation. In order to do this, the memory
must be aligned in such a way that the executing logic can simply
mask the current stack pointer to get the beginning of the stack
allocation.
The advantage of using an aligned stack is no OS interface need
be called to get the beginning of the stack. It is simply and
AND operation on the current stack pointer. The disadvantages
are that the alignment (1) causes memory fragmentation which
be a serious problem for memory limited systems, and (2) limits
the maximum size of the stack. Any mask places a limit on the
maximum size of the stack; stack sizes about that would map to
an incorrect address.
In general, CONFIG_TLS_ALIGNED is preferred for the KERNEL
build where the virtualized stack address an be aligned with
no implications to physical memory. In other builds, the
unaligned stack implementation is usually superior.
config TLS_LOG2_MAXSTACK
int "Maximum stack size (log2)"
default 13
range 11 24
depends on TLS_ALIGNED
---help---
Stack based TLS works by fetch thread information from the beginning
of the stack memory allocation. In order to do this, the memory
must be aligned in such a way that the executing logic can simply
masking the current stack pointer to get the beginning of the stack
allocation.
This setting specifies the alignment of the stack as a power of 2:
11=2KB, 12=4KB, 13=8KB, etc. The exact alignment is not so critical
except that (1) a very large value can cause you to run out of