b6a48d2a4b
commit f025692c99 ("accel/tcg: Clear PAGE_WRITE before translation")
fixed cross-modifying code handling, but did not add a test. The
changed code was further improved recently [1], and I was not sure
whether these modifications were safe (spoiler: they were fine).
Add a test to make sure there are no regressions.
[1] https://lists.gnu.org/archive/html/qemu-devel/2022-09/msg00034.html
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Message-Id: <20241001150617.9977-1-iii@linux.ibm.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20241023113406.1284676-8-alex.bennee@linaro.org>
81 lines
1.9 KiB
C
81 lines
1.9 KiB
C
/*
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* Test patching code, running in one thread, from another thread.
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*
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* Intel SDM calls this "cross-modifying code" and recommends a special
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* sequence, which requires both threads to cooperate.
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*
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* Linux kernel uses a different sequence that does not require cooperation and
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* involves patching the first byte with int3.
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*
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* Finally, there is user-mode software out there that simply uses atomics, and
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* that seems to be good enough in practice. Test that QEMU has no problems
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* with this as well.
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*/
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#include <assert.h>
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#include <pthread.h>
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#include <stdbool.h>
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#include <stdlib.h>
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void add1_or_nop(long *x);
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asm(".pushsection .rwx,\"awx\",@progbits\n"
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".globl add1_or_nop\n"
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/* addq $0x1,(%rdi) */
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"add1_or_nop: .byte 0x48, 0x83, 0x07, 0x01\n"
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"ret\n"
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".popsection\n");
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#define THREAD_WAIT 0
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#define THREAD_PATCH 1
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#define THREAD_STOP 2
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static void *thread_func(void *arg)
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{
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int val = 0x0026748d; /* nop */
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while (true) {
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switch (__atomic_load_n((int *)arg, __ATOMIC_SEQ_CST)) {
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case THREAD_WAIT:
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break;
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case THREAD_PATCH:
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val = __atomic_exchange_n((int *)&add1_or_nop, val,
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__ATOMIC_SEQ_CST);
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break;
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case THREAD_STOP:
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return NULL;
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default:
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assert(false);
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__builtin_unreachable();
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}
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}
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}
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#define INITIAL 42
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#define COUNT 1000000
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int main(void)
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{
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int command = THREAD_WAIT;
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pthread_t thread;
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long x = 0;
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int err;
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int i;
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err = pthread_create(&thread, NULL, &thread_func, &command);
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assert(err == 0);
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__atomic_store_n(&command, THREAD_PATCH, __ATOMIC_SEQ_CST);
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for (i = 0; i < COUNT; i++) {
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add1_or_nop(&x);
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}
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__atomic_store_n(&command, THREAD_STOP, __ATOMIC_SEQ_CST);
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err = pthread_join(thread, NULL);
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assert(err == 0);
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assert(x >= INITIAL);
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assert(x <= INITIAL + COUNT);
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return EXIT_SUCCESS;
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}
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