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

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>

2 files changed, 77 insertions, 1 deletions

diff --git a/tests/tcg/x86_64/Makefile.target b/tests/tcg/x86_64/Makefile.target
index 6177fd845a..861a0966f4 100644
--- a/tests/tcg/x86_64/Makefile.target
+++ b/tests/tcg/x86_64/Makefile.target
@@ -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)
diff --git a/tests/tcg/x86_64/noexec.c b/tests/tcg/x86_64/noexec.c
new file mode 100644
index 0000000000..9b124901be
--- /dev/null
+++ b/tests/tcg/x86_64/noexec.c
@@ -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]));
+}