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MIPS,prctl: add PR_[GS]ET_FP_MODE prctl options for MIPS

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Userland code may be built using an ABI which permits linking to objects
that have more restrictive floating point requirements. For example,
userland code may be built to target the O32 FPXX ABI. Such code may be
linked with other FPXX code, or code built for either one of the more
restrictive FP32 or FP64. When linking with more restrictive code, the
overall requirement of the process becomes that of the more restrictive
code. The kernel has no way to know in advance which mode the process
will need to be executed in, and indeed it may need to change during
execution. The dynamic loader is the only code which will know the
overall required mode, and so it needs to have a means to instruct the
kernel to switch the FP mode of the process.

This patch introduces 2 new options to the prctl syscall which provide
such a capability. The FP mode of the process is represented as a
simple bitmask combining a number of mode bits mirroring those present
in the hardware. Userland can either retrieve the current FP mode of
the process:

  mode = prctl(PR_GET_FP_MODE);

or modify the current FP mode of the process:

  err = prctl(PR_SET_FP_MODE, new_mode);

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Matthew Fortune <matthew.fortune@imgtec.com>
Cc: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8899/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
This commit is contained in:
Paul Burton 2015-01-08 12:17:37 +00:00 • committed by Ralf Baechle
parent ae58d882bf
commit 9791554b45
7 changed files with 144 additions and 0 deletions
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5
include/uapi/linux/prctl.h
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@ -185,4 +185,9 @@ struct prctl_mm_map {
#define PR_MPX_ENABLE_MANAGEMENT 43
#define PR_MPX_DISABLE_MANAGEMENT 44
#define PR_SET_FP_MODE 45
#define PR_GET_FP_MODE 46
# define PR_FP_MODE_FR (1 << 0) /* 64b FP registers */
# define PR_FP_MODE_FRE (1 << 1) /* 32b compatibility */
#endif /* _LINUX_PRCTL_H */