[PATCH] malloc: Correct the documentation of the top_pad default
Siddhesh Poyarekar
siddhesh@gotplt.org
Thu Aug 4 14:51:22 GMT 2022
On 2022-08-04 04:48, Florian Weimer via Libc-alpha wrote:
> DEFAULT_TOP_PAD is defined as 131072 in
> sysdeps/generic/malloc-machine.h.
LGTM, but I wonder if we should tighten this so that it doesn't appear
that DEFAULT_TOP_PAD could be 0 in any of our build configurations.
e.g. we could replace the definition with a #error "define
DEFAULT_TOP_PAD" or something like that to ensure that it's always
defined through malloc-machine.h. What do you think?
Thanks,
Sid
>
> ---
> elf/dl-tunables.list | 1 +
> elf/tst-rtld-list-tunables.exp | 2 +-
> manual/tunables.texi | 2 +-
> 3 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/elf/dl-tunables.list b/elf/dl-tunables.list
> index e6a56b3070..e925590c36 100644
> --- a/elf/dl-tunables.list
> +++ b/elf/dl-tunables.list
> @@ -42,6 +42,7 @@ glibc {
> type: SIZE_T
> env_alias: MALLOC_TOP_PAD_
> security_level: SXID_IGNORE
> + default: 131072
> }
> perturb {
> type: INT_32
> diff --git a/elf/tst-rtld-list-tunables.exp b/elf/tst-rtld-list-tunables.exp
> index cdfdb56a94..2233ea9c7c 100644
> --- a/elf/tst-rtld-list-tunables.exp
> +++ b/elf/tst-rtld-list-tunables.exp
> @@ -9,7 +9,7 @@ glibc.malloc.perturb: 0 (min: 0, max: 255)
> glibc.malloc.tcache_count: 0x0 (min: 0x0, max: 0x[f]+)
> glibc.malloc.tcache_max: 0x0 (min: 0x0, max: 0x[f]+)
> glibc.malloc.tcache_unsorted_limit: 0x0 (min: 0x0, max: 0x[f]+)
> -glibc.malloc.top_pad: 0x0 (min: 0x0, max: 0x[f]+)
> +glibc.malloc.top_pad: 0x20000 (min: 0x0, max: 0x[f]+)
> glibc.malloc.trim_threshold: 0x0 (min: 0x0, max: 0x[f]+)
> glibc.rtld.dynamic_sort: 2 (min: 1, max: 2)
> glibc.rtld.nns: 0x4 (min: 0x1, max: 0x10)
> diff --git a/manual/tunables.texi b/manual/tunables.texi
> index 83cdcdac6d..ffd50a3fe2 100644
> --- a/manual/tunables.texi
> +++ b/manual/tunables.texi
> @@ -143,7 +143,7 @@ number of bytes to retain when shrinking any of the arenas. This provides the
> necessary hysteresis in heap size such that excessive amounts of system calls
> can be avoided.
>
> -The default value of this tunable is @samp{0}.
> +The default value of this tunable is @samp{131072} (128 KB).
> @end deftp
>
> @deftp Tunable glibc.malloc.perturb
>
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