prctl.2: srcfix: add comments for navigation

The prctl.2 source is unnecessarily hard to navigate, not least
because prctl option flags are traditionally named PR_* and so look
just like prctl names.

For each actual prctl, add a comment of the form

	.\" prctl PR_FOO

to make it move obvious where each top-level prctl starts.

Of course, we could add some clever macros, but let's not confuse
dumb parsers.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/prctl.2

@@ -77,6 +77,7 @@ is called with a first argument describing what to do
 arguments with a significance depending on the first one.
 The first argument can be:
 .\"
+.\" prctl PR_CAP_AMBIENT
 .TP
 .BR PR_CAP_AMBIENT " (since Linux 4.3)"
 .\" commit 58319057b7847667f0c9585b9de0e8932b0fdb08
@@ -130,6 +131,7 @@ library in the form of
 .BR cap_set_ambient (3),
 and
 .BR cap_reset_ambient (3).
+.\" prctl PR_CAPBSET_READ
 .TP
 .BR PR_CAPBSET_READ " (since Linux 2.6.25)"
 Return (as the function result) 1 if the capability specified in
@@ -152,6 +154,7 @@ A higher-level interface layered on top of this operation is provided in the
 .BR libcap (3)
 library in the form of
 .BR cap_get_bound (3).
+.\" prctl PR_CAPBSET_DROP
 .TP
 .BR PR_CAPBSET_DROP " (since Linux 2.6.25)"
 If the calling thread has the
@@ -178,6 +181,7 @@ A higher-level interface layered on top of this operation is provided in the
 .BR libcap (3)
 library in the form of
 .BR cap_drop_bound (3).
+.\" prctl PR_SET_CHILD_SUBREAPER
 .TP
 .BR PR_SET_CHILD_SUBREAPER " (since Linux 3.4)"
 .\" commit ebec18a6d3aa1e7d84aab16225e87fd25170ec2b
@@ -224,11 +228,13 @@ Some
 frameworks (e.g.,
 .BR systemd (1))
 employ a subreaper process for similar reasons.
+.\" prctl PR_GET_CHILD_SUBREAPER
 .TP
 .BR PR_GET_CHILD_SUBREAPER " (since Linux 3.4)"
 Return the "child subreaper" setting of the caller,
 in the location pointed to by
 .IR "(int\ *) arg2" .
+.\" prctl PR_SET_DUMPABLE
 .TP
 .BR PR_SET_DUMPABLE " (since Linux 2.3.20)"
 Set the state of the "dumpable" attribute,
@@ -297,6 +303,7 @@ the ownership of files in the process's
 .IR /proc/[pid]
 directory is affected as described in
 .BR proc (5).
+.\" prctl PR_GET_DUMPABLE
 .TP
 .BR PR_GET_DUMPABLE " (since Linux 2.3.20)"
 Return (as the function result) the current state of the calling
@@ -304,6 +311,7 @@ process's dumpable attribute.
 .\" Since Linux 2.6.13, the dumpable flag can have the value 2,
 .\" but in 2.6.13 PR_GET_DUMPABLE simply returns 1 if the dumpable
 .\" flags has a nonzero value.  This was fixed in 2.6.14.
+.\" prctl PR_SET_ENDIAN
 .TP
 .BR PR_SET_ENDIAN " (since Linux 2.6.18, PowerPC only)"
 Set the endian-ness of the calling process to the value given
@@ -314,11 +322,13 @@ in \fIarg2\fP, which should be one of the following:
 or
 .B PR_ENDIAN_PPC_LITTLE
 (PowerPC pseudo little endian).
+.\" prctl PR_GET_ENDIAN
 .TP
 .BR PR_GET_ENDIAN " (since Linux 2.6.18, PowerPC only)"
 Return the endian-ness of the calling process,
 in the location pointed to by
 .IR "(int\ *) arg2" .
+.\" prctl PR_SET_FP_MODE
 .TP
 .BR PR_SET_FP_MODE " (since Linux 4.0, only on MIPS)"
 .\" commit 9791554b45a2acc28247f66a5fd5bbc212a6b8c8
@@ -425,6 +435,7 @@ The arguments
 and
 .IR arg5
 are ignored.
+.\" prctl PR_GET_FP_MODE
 .TP
 .BR PR_GET_FP_MODE " (since Linux 4.0, only on MIPS)"
 Return (as the function result)
@@ -442,6 +453,7 @@ The arguments
 and
 .IR arg5
 are ignored.
+.\" prctl PR_SET_FPEMU
 .TP
 .BR PR_SET_FPEMU " (since Linux 2.4.18, 2.5.9, only on ia64)"
 Set floating-point emulation control bits to \fIarg2\fP.
@@ -452,11 +464,13 @@ to silently emulate floating-point operation accesses, or
 to not emulate floating-point operations and send
 .B SIGFPE
 instead.
+.\" prctl PR_GET_FPEMU
 .TP
 .BR PR_GET_FPEMU " (since Linux 2.4.18, 2.5.9, only on ia64)"
 Return floating-point emulation control bits,
 in the location pointed to by
 .IR "(int\ *) arg2" .
+.\" prctl PR_SET_FPEXC
 .TP
 .BR PR_SET_FPEXC " (since Linux 2.4.21, 2.5.32, only on PowerPC)"
 Set floating-point exception mode to \fIarg2\fP.
@@ -470,11 +484,13 @@ Pass \fBPR_FP_EXC_SW_ENABLE\fP to use FPEXC for FP exception enables,
 \fBPR_FP_EXC_NONRECOV\fP for async nonrecoverable exception mode,
 \fBPR_FP_EXC_ASYNC\fP for async recoverable exception mode,
 \fBPR_FP_EXC_PRECISE\fP for precise exception mode.
+.\" prctl PR_GET_FPEXC
 .TP
 .BR PR_GET_FPEXC " (since Linux 2.4.21, 2.5.32, only on PowerPC)"
 Return floating-point exception mode,
 in the location pointed to by
 .IR "(int\ *) arg2" .
+.\" prctl PR_SET_KEEPCAPS
 .TP
 .BR PR_SET_KEEPCAPS " (since Linux 2.2.18)"
 Set the state of the calling thread's "keep capabilities" flag.
@@ -485,6 +501,7 @@ must be either 0 (clear the flag)
 or 1 (set the flag).
 The "keep capabilities" value will be reset to 0 on subsequent calls to
 .BR execve (2).
+.\" prctl PR_GET_KEEPCAPS
 .TP
 .BR PR_GET_KEEPCAPS " (since Linux 2.2.18)"
 Return (as the function result) the current state of the calling thread's
@@ -492,6 +509,7 @@ Return (as the function result) the current state of the calling thread's
 See
 .BR capabilities (7)
 for a description of this flag.
+.\" prctl PR_MCE_KILL
 .TP
 .BR PR_MCE_KILL " (since Linux 2.6.32)"
 Set the machine check memory corruption kill policy for the calling thread.
@@ -532,6 +550,7 @@ The policy is inherited by children.
 The remaining unused
 .BR prctl ()
 arguments must be zero for future compatibility.
+.\" prctl PR_MCE_KILL_GET
 .TP
 .BR PR_MCE_KILL_GET " (since Linux 2.6.32)"
 Return (as the function result)
@@ -539,6 +558,7 @@ the current per-process machine check kill policy.
 All unused
 .BR prctl ()
 arguments must be zero.
+.\" prctl PR_SET_MM
 .TP
 .BR PR_SET_MM " (since Linux 3.3)"
 .\" commit 028ee4be34a09a6d48bdf30ab991ae933a7bc036
@@ -716,6 +736,7 @@ This feature is available only if the kernel is built with the
 .BR CONFIG_CHECKPOINT_RESTORE
 option enabled.
 .RE
+.\" prctl PR_MPX_ENABLE_MANAGEMENT
 .TP
 .BR PR_MPX_ENABLE_MANAGEMENT ", " PR_MPX_DISABLE_MANAGEMENT " (since Linux 3.19) "
 .\" commit fe3d197f84319d3bce379a9c0dc17b1f48ad358c
@@ -791,6 +812,7 @@ had been called.
 .IP
 For further information on Intel MPX, see the kernel source file
 .IR Documentation/x86/intel_mpx.txt .
+.\" prctl PR_SET_NAME
 .TP
 .BR PR_SET_NAME " (since Linux 2.6.9)"
 Set the name of the calling thread,
@@ -819,6 +841,7 @@ in the buffer pointed to by
 .IR "(char\ *) arg2" .
 The buffer should allow space for up to 16 bytes;
 the returned string will be null-terminated.
+.\" prctl PR_SET_NO_NEW_PRIVS
 .TP
 .BR PR_SET_NO_NEW_PRIVS " (since Linux 3.5)"
 Set the calling thread's
@@ -862,6 +885,7 @@ For more information, see the kernel source file
 before Linux 4.13).
 See also
 .BR seccomp (2).
+.\" prctl PR_GET_NO_NEW_PRIVS
 .TP
 .BR PR_GET_NO_NEW_PRIVS " (since Linux 3.5)"
 Return (as the function result) the value of the
@@ -873,6 +897,7 @@ behavior.
 A value of 1 indicates
 .BR execve (2)
 will operate in the privilege-restricting mode described above.
+.\" prctl PR_SET_PDEATHSIG
 .TP
 .BR PR_SET_PDEATHSIG " (since Linux 2.1.57)"
 Set the parent-death signal
@@ -922,11 +947,13 @@ or a binary that has associated capabilities (see
 .BR capabilities (7));
 otherwise, this value is preserved across
 .BR execve (2).
+.\" prctl PR_GET_PDEATHSIG
 .TP
 .BR PR_GET_PDEATHSIG " (since Linux 2.3.15)"
 Return the current value of the parent process death signal,
 in the location pointed to by
 .IR "(int\ *) arg2" .
+.\" prctl PR_SET_PTRACER
 .TP
 .BR PR_SET_PTRACER " (since Linux 3.4)"
 .\" commit 2d514487faf188938a4ee4fb3464eeecfbdcf8eb
@@ -959,6 +986,7 @@ For further information, see the kernel source file
 (or
 .IR Documentation/security/Yama.txt
 before Linux 4.13).
+.\" prctl PR_SET_SECCOMP
 .TP
 .BR PR_SET_SECCOMP " (since Linux 2.6.23)"
 .\" See http://thread.gmane.org/gmane.linux.kernel/542632
@@ -1035,6 +1063,7 @@ For further information, see the kernel source file
 (or
 .IR Documentation/prctl/seccomp_filter.txt
 before Linux 4.13).
+.\" prctl PR_GET_SECCOMP
 .TP
 .BR PR_GET_SECCOMP " (since Linux 2.6.23)"
 Return (as the function result)
@@ -1061,18 +1090,21 @@ field of the
 file provides a method of obtaining the same information,
 without the risk that the process is killed; see
 .BR proc (5).
+.\" prctl PR_SET_SECUREBITS
 .TP
 .BR PR_SET_SECUREBITS " (since Linux 2.6.26)"
 Set the "securebits" flags of the calling thread to the value supplied in
 .IR arg2 .
 See
 .BR capabilities (7).
+.\" prctl PR_GET_SECUREBITS
 .TP
 .BR PR_GET_SECUREBITS " (since Linux 2.6.26)"
 Return (as the function result)
 the "securebits" flags of the calling thread.
 See
 .BR capabilities (7).
+.\" prctl PR_GET_SPECULATION_CTRL
 .TP
 .BR PR_GET_SPECULATION_CTRL " (since Linux 4.17)"
 Return (as the function result)
@@ -1119,6 +1151,7 @@ and
 .I arg5
 arguments must be specified as 0; otherwise the call fails with the error
 .BR EINVAL .
+.\" prctl PR_SET_SPECULATION_CTRL
 .TP
 .BR PR_SET_SPECULATION_CTRL " (since Linux 4.17)"
 .\" commit b617cfc858161140d69cc0b5cc211996b557a1c7
@@ -1174,6 +1207,7 @@ call failing with the error
 .BR ENXIO .
 For further details, see the kernel source file
 .IR Documentation/admin-guide/kernel-parameters.txt .
+.\" prctl PR_SET_THP_DISABLE
 .TP
 .BR PR_SET_THP_DISABLE " (since Linux 3.15)"
 .\" commit a0715cc22601e8830ace98366c0c2bd8da52af52
@@ -1191,6 +1225,7 @@ The setting of the "THP disable" flag is inherited by a child created via
 and is preserved across
 .BR execve (2).
 .\"
+.\" prctl PR_TASK_PERF_EVENTS_DISABLE
 .TP
 .BR PR_TASK_PERF_EVENTS_DISABLE " (since Linux 2.6.31)"
 Disable all performance counters attached to the calling process,
@@ -1207,6 +1242,7 @@ Originally called
 renamed (retaining the same numerical value)
 in Linux 2.6.32.
 .\"
+.\" prctl PR_TASK_PERF_EVENTS_ENABLE
 .TP
 .BR PR_TASK_PERF_EVENTS_ENABLE " (since Linux 2.6.31)"
 The converse of
@@ -1220,11 +1256,13 @@ renamed
 .\" commit cdd6c482c9ff9c55475ee7392ec8f672eddb7be6
 in Linux 2.6.32.
 .\"
+.\" prctl PR_GET_THP_DISABLE
 .TP
 .BR PR_GET_THP_DISABLE " (since Linux 3.15)"
 Return (as the function result) the current setting of the "THP disable"
 flag for the calling thread:
 either 1, if the flag is set, or 0, if it is not.
+.\" prctl PR_GET_TID_ADDRESS
 .TP
 .BR PR_GET_TID_ADDRESS " (since Linux 3.5)"
 .\" commit 300f786b2683f8bb1ec0afb6e1851183a479c86d
@@ -1246,6 +1284,7 @@ system call does not have a compat implementation for
 the AMD64 x32 and MIPS n32 ABIs,
 and the kernel writes out a pointer using the kernel's pointer size,
 this operation expects a user-space buffer of 8 (not 4) bytes on these ABIs.
+.\" prctl PR_SET_TIMERSLACK
 .TP
 .BR PR_SET_TIMERSLACK " (since Linux 2.6.28)"
 .\" See https://lwn.net/Articles/369549/
@@ -1316,10 +1355,12 @@ can be examined and changed via the file
 .IR /proc/[pid]/timerslack_ns .
 See
 .BR proc (5).
+.\" prctl PR_GET_TIMERSLACK
 .TP
 .BR PR_GET_TIMERSLACK " (since Linux 2.6.28)"
 Return (as the function result)
 the "current" timer slack value of the calling thread.
+.\" prctl PR_SET_TIMING
 .TP
 .BR PR_SET_TIMING " (since Linux 2.6.0)"
 .\" Precisely: Linux 2.6.0-test4
@@ -1338,11 +1379,13 @@ is not currently implemented
 .\" PR_TIMING_TIMESTAMP doesn't do anything in 2.6.26-rc8,
 .\" and looking at the patch history, it appears
 .\" that it never did anything.
+.\" prctl PR_GET_TIMING
 .TP
 .BR PR_GET_TIMING " (since Linux 2.6.0)"
 .\" Precisely: Linux 2.6.0-test4
 Return (as the function result) which process timing method is currently
 in use.
+.\" prctl PR_SET_TSC
 .TP
 .BR PR_SET_TSC " (since Linux 2.6.26, x86 only)"
 Set the state of the flag determining whether the timestamp counter
@@ -1356,12 +1399,14 @@ to allow it to be read, or
 to generate a
 .B SIGSEGV
 when the process tries to read the timestamp counter.
+.\" prctl PR_GET_TSC
 .TP
 .BR PR_GET_TSC " (since Linux 2.6.26, x86 only)"
 Return the state of the flag determining whether the timestamp counter
 can be read,
 in the location pointed to by
 .IR "(int\ *) arg2" .
+.\" prctl PR_SET_UNALIGN
 .TP
 .B PR_SET_UNALIGN
 (Only on: ia64, since Linux 2.3.48; parisc, since Linux 2.6.15;
@@ -1385,6 +1430,7 @@ flag in
 operation of the
 .BR setsysinfo ()
 system call on Tru64).
+.\" prctl PR_GET_UNALIGN
 .TP
 .B PR_GET_UNALIGN
 (See
@@ -1392,6 +1438,7 @@ system call on Tru64).
 for information on versions and architectures.)
 Return unaligned access control bits, in the location pointed to by
 .IR "(unsigned int\ *) arg2" .
+.\" prctl PR_SET_IO_FLUSHER
 .TP
 .BR PR_SET_IO_FLUSHER " (since Linux 5.6)"
 If a user process is involved in the block layer or filesystem I/O path,
@@ -1420,6 +1467,7 @@ and is preserved across
 Examples of IO_FLUSHER applications are FUSE daemons, SCSI device
 emulation daemons, and daemons that perform error handling like multipath
 path recovery applications.
+.\" prctl PR_GET_IO_FLUSHER
 .TP
 .B PR_GET_IO_FLUSHER (Since Linux 5.6)
 Return (as the function result) the IO_FLUSHER state of the caller.