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target/i386: Make translator stop before the end of a page

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Right now translator stops right *after* the end of a page, which
breaks reporting of fault locations when the last instruction of a
multi-insn translation block crosses a page boundary.

An implementation, like the one arm and s390x have, would require an
i386 length disassembler, which is burdensome to maintain. Another
alternative would be to single-step at the end of a guest page, but
this may come with a performance impact.

Fix by snapshotting disassembly state and restoring it after we figure
out we crossed a page boundary. This includes rolling back cc_op
updates and emitted ops.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1143
Message-Id: <20220817150506.592862-4-iii@linux.ibm.com>
[rth: Simplify end-of-insn cross-page checks.]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Ilya Leoshkevich 2022-08-17 17:05:05 +02:00 • committed by Richard Henderson
parent ab12c95d3f
commit 950936681f
3 changed files with 116 additions and 26 deletions
Download patch file Download diff file Expand all files Collapse all files

3
tests/tcg/x86_64/Makefile.target
View file

@ -10,6 +10,7 @@ include $(SRC_PATH)/tests/tcg/i386/Makefile.target
ifeq ($(filter %-linux-user, $(TARGET)),$(TARGET))
X86_64_TESTS += vsyscall
X86_64_TESTS += noexec
TESTS=$(MULTIARCH_TESTS) $(X86_64_TESTS) test-x86_64
else
TESTS=$(MULTIARCH_TESTS)
@ -23,5 +24,5 @@ test-x86_64: LDFLAGS+=-lm -lc
test-x86_64: test-i386.c test-i386.h test-i386-shift.h test-i386-muldiv.h
$(CC) $(CFLAGS) $< -o $@ $(LDFLAGS)
vsyscall: $(SRC_PATH)/tests/tcg/x86_64/vsyscall.c
%: $(SRC_PATH)/tests/tcg/x86_64/%.c
$(CC) $(CFLAGS) $< -o $@ $(LDFLAGS)

75
tests/tcg/x86_64/noexec.c Normal file
View file

@ -0,0 +1,75 @@
#include "../multiarch/noexec.c.inc"
static void *arch_mcontext_pc(const mcontext_t *ctx)
{
return (void *)ctx->gregs[REG_RIP];
}
int arch_mcontext_arg(const mcontext_t *ctx)
{
return ctx->gregs[REG_RDI];
}
static void arch_flush(void *p, int len)
{
}
extern char noexec_1[];
extern char noexec_2[];
extern char noexec_end[];
asm("noexec_1:\n"
" movq $1,%rdi\n" /* %rdi is 0 on entry, set 1. */
"noexec_2:\n"
" movq $2,%rdi\n" /* %rdi is 0/1; set 2. */
" ret\n"
"noexec_end:");
int main(void)
{
struct noexec_test noexec_tests[] = {
{
.name = "fallthrough",
.test_code = noexec_1,
.test_len = noexec_end - noexec_1,
.page_ofs = noexec_1 - noexec_2,
.entry_ofs = noexec_1 - noexec_2,
.expected_si_ofs = 0,
.expected_pc_ofs = 0,
.expected_arg = 1,
},
{
.name = "jump",
.test_code = noexec_1,
.test_len = noexec_end - noexec_1,
.page_ofs = noexec_1 - noexec_2,
.entry_ofs = 0,
.expected_si_ofs = 0,
.expected_pc_ofs = 0,
.expected_arg = 0,
},
{
.name = "fallthrough [cross]",
.test_code = noexec_1,
.test_len = noexec_end - noexec_1,
.page_ofs = noexec_1 - noexec_2 - 2,
.entry_ofs = noexec_1 - noexec_2 - 2,
.expected_si_ofs = 0,
.expected_pc_ofs = -2,
.expected_arg = 1,
},
{
.name = "jump [cross]",
.test_code = noexec_1,
.test_len = noexec_end - noexec_1,
.page_ofs = noexec_1 - noexec_2 - 2,
.entry_ofs = -2,
.expected_si_ofs = 0,
.expected_pc_ofs = -2,
.expected_arg = 0,
},
};
return test_noexec(noexec_tests,
sizeof(noexec_tests) / sizeof(noexec_tests[0]));
}