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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | EXAMPLES | STANDARDS | HISTORY | SEE ALSO | COLOPHON |
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PR_RISCV_SET...CHE_FLUSH_CTX(2const) PR_RISCV_SET...CHE_FLUSH_CTX(2const)
PR_RISCV_SET_ICACHE_FLUSH_CTX - Enable/disable icache flushing
instructions in userspace.
Standard C library (libc, -lc)
#include <linux/prctl.h> /* Definition of PR_* constants */
#include <sys/prctl.h>
int prctl(PR_RISCV_SET_ICACHE_FLUSH_CTX, unsigned long ctx,
unsigned long scope);
The context and the scope can be provided using ctx and scope
respectively.
When scope is set to PR_RISCV_SCOPE_PER_PROCESS all threads in the
process are permitted to emit icache flushing instructions.
Whenever any thread in the process is migrated, the corresponding
hart's icache will be guaranteed to be consistent with instruction
storage. This does not enforce any guarantees outside of
migration. If a thread modifies an instruction that another
thread may attempt to execute, the other thread must still emit an
icache flushing instruction before attempting to execute the
potentially modified instruction. This must be performed by the
user-space program.
In per-thread context (eg. scope is set to
PR_RISCV_SCOPE_PER_THREAD) only the thread calling this function
is permitted to emit icache flushing instructions. When the
thread is migrated, the corresponding hart's icache will be
guaranteed to be consistent with instruction storage.
On kernels configured without SMP, this prctl
PR_RISCV_SET_ICACHE_FLUSH_CTX is a nop as migrations across harts
will not occur.
The following values for ctx can be specified:
PR_RISCV_CTX_SW_FENCEI_ON (since Linux 6.10)
Allow fence.i in user space.
PR_RISCV_CTX_SW_FENCEI_OFF (since Linux 6.10)
Disallow fence.i in user space. All threads in a process
will be affected when scope is set to
PR_RISCV_SCOPE_PER_PROCESS. Therefore, caution must be
taken; use this flag only when you can guarantee that no
thread in the process will emit fence.i from this point
onward.
The following values for scope can be specified:
PR_RISCV_SCOPE_PER_PROCESS (since Linux 6.10)
Ensure the icache of any thread in this process is coherent
with instruction storage upon migration.
PR_RISCV_SCOPE_PER_THREAD (since Linux 6.10)
Ensure the icache of the current thread is coherent with
instruction storage upon migration.
The following files are meant to be compiled and linked with each
other. The modify_instruction() function replaces an add with
zero with an add with one, causing the instruction sequence in
get_value() to change from returning a zero to returning a one.
Program source: cmodx.c
#include <stdio.h>
#include <sys/prctl.h>
extern int get_value(void);
extern void modify_instruction(void);
int
main(void)
{
int value = get_value();
printf("Value before cmodx: %d\n", value);
// Call prctl before first fence.i is called
prctl(PR_RISCV_SET_ICACHE_FLUSH_CTX, PR_RISCV_CTX_SW_FENCEI_ON,
PR_RISCV_SCOPE_PER_PROCESS);
modify_instruction();
// Call prctl after final fence.i is called in process
prctl(PR_RISCV_SET_ICACHE_FLUSH_CTX, PR_RISCV_CTX_SW_FENCEI_OFF,
PR_RISCV_SCOPE_PER_PROCESS);
value = get_value();
printf("Value after cmodx: %d\n", value);
return 0;
}
Program source: cmodx.S
.option norvc
.text
.global modify_instruction
modify_instruction:
lw a0, new_insn
lui a5,%hi(old_insn)
sw a0,%lo(old_insn)(a5)
fence.i
ret
.section modifiable, "awx"
.global get_value
get_value:
li a0, 0
old_insn:
addi a0, a0, 0
ret
.data
new_insn:
addi a0, a0, 1
Expected result
Value before cmodx: 0
Value after cmodx: 1
Linux. RISC-V only.
Linux 6.10 (RISC-V).
prctl(2)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.10.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-02-02. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.10 2024-0P7R-_2R3ISCV_SET...CHE_FLUSH_CTX(2const)
Pages that refer to this page: prctl(2)
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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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