[alsa-devel] [alsa-lib][PATCH 00/34] pcm/conf/alisp: replace usage of alloca() with automatic variables

[Takashi Sakamoto]

Hi,

A batch of this patchset is to save storage consumption and to improve
execution performance, just for a little.

Currently, ALSA userspace library doesn't disclose layouts of major 
structures to applications. The applications call some APIs in the
library to get memory objects for the structures, then operates to
corresponding opaque pointers. In most cases, the objects are kept on
stack by calls of alloca(3).

On the other hand, inner the library, the layouts are decided in
pre-compile or compile time. Therefore, there's little needs to call
of alloca(3).

However, inner the library, we can see some usages of alloca(3). This
brings two disadvantages to system. One is to execute more instructions
to use stack than automatic variables, for the same task. Another is to
enlarge size of shared object. Although both disadvantages are not so
remarkable, it's better to improve them.

This patchset replaces usages of alloca() with automatic variables just
to raw structures. Additionally, this commit improves code formats in
related functions.

I can see below effect on my environment (Ubuntu 16.04, amd64, gcc)
$ git checkout master
$ git show HEAD
commit 941bd150bef2560f3e38a3bf74d546447e3126d1
...
$ ./gitcompile --with-plugindir=/usr/lib/x86_64-linux-gnu/alsa-lib/
...
$ ls -l src/.libs/libasound.so.2.0.0 
-rwxrwxr-x 1 mocchi mocchi 4794528  7月 14 22:22 src/.libs/libasound.so.2.0.0
$ git checkout remove-alloca-asound
$ make
...
$ ls -l src/.libs/libasound.so.2.0.0 
-rwxrwxr-x 1 mocchi mocchi 4783712  7月 14 22:21 src/.libs/libasound.so.2.0.0
$ gcc -v
...
gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.1)

Takashi Sakamoto (34):
  pcm: change code formatting for snd_pcm_set_params()
  pcm: remove alloca() from snd_pcm_set_params()
  pcm: change code formatting for snd_pcm_get_params()
  pcm: remove alloca() from snd_pcm_get_params
  pcm: change code formatting for snd_pcm_direct_initialize_slave()
  pcm: remove alloca() from snd_pcm_direct_initialize_slave
  pcm: change code formatting for snd_pcm_direct_initialize_poll_fd()
  pcm: remove alloca() from snd_pcm_direct_initialize_poll_fd()
  pcm: change code formatting for snd_pcm_direct_set_timer_params()
  pcm: remove alloca() from snd_pcm_direct_set_timer_params
  pcm: remove alloca() from _snd_pcm_hook_ctl_elems_install()
  pcm: change code formatting for snd_pcm_hw_change_timer()
  pcm: remove alloca() from snd_pcm_hw_change_timer()
  pcm: remove alloca() from snd_pcm_query_chmaps_from_hw()
  pcm: remove alloca() from snd_pcm_hw_get_chmap()
  pcm: remove alloca() from snd_pcm_hw_set_chmap()
  pcm: remove alloca() from snd_spcm_init()
  pcm: remove alloca() from snd_spcm_init_duplex()
  pcm: change code formatting for softvol_load_control()
  pcm: remove alloca() from softvol_load_control()
  pcm: change code formatting for _snd_pcm_softvol_open()
  pcm: remove alloca() from _snd_pcm_softvol_open()
  conf: remove alloca() from snd_determine_driver()
  conf: remove alloca() from snd_func_card_id()
  conf: remove alloca() from snd_func_card_name()
  conf: remove alloca() from snd_func_pcm_id()
  conf: remove alloca() from snd_func_pcm_args_by_class()
  conf: remove alloca() from snd_func_private_pcm_subdevice()
  alisp: remove alloca() from FA_card_info()
  alisp: remove alloca() from FA_hctl_find_elem()
  alisp: remove alloca() from FA_hctl_elem_info()
  alisp: remove alloca() from FA_hctl_elem_read()
  alisp: remove alloca() from FA_hctl_elem_write()
  alisp: remove alloca() from FA_pcm_info()

 src/alisp/alisp_snd.c | 153 ++++++++++++++++-----------------
 src/confmisc.c        |  51 +++++------
 src/pcm/pcm.c         | 232 ++++++++++++++++++++++++++++----------------------
 src/pcm/pcm_direct.c  | 132 ++++++++++++++++------------
 src/pcm/pcm_hooks.c   |   8 +-
 src/pcm/pcm_hw.c      |  74 +++++++++-------
 src/pcm/pcm_simple.c  |  22 ++---
 src/pcm/pcm_softvol.c |  69 ++++++++-------
 8 files changed, 393 insertions(+), 348 deletions(-)

-- 
2.7.4