Fix pc/function name for signal handler frame.

This refactors the step function slightly to split it up into
distinct pieces since the code needs to handle a signal handler
versus normal step slightly differently.

Add a new error for an invalid elf.

Modify libbacktrace code to handle new error code.

Bug: 130302288

Test: libbacktrace/libunwindstack unit tests.
Change-Id: I3fb9b00c02d2cf2cc5911541bba0346c6f39b8e6
diff --git a/libunwindstack/tests/ElfTest.cpp b/libunwindstack/tests/ElfTest.cpp
index 23c9cf8..c432d6d 100644
--- a/libunwindstack/tests/ElfTest.cpp
+++ b/libunwindstack/tests/ElfTest.cpp
@@ -132,8 +132,12 @@
   uint64_t func_offset;
   ASSERT_FALSE(elf.GetFunctionName(0, &name, &func_offset));
 
+  ASSERT_FALSE(elf.StepIfSignalHandler(0, nullptr, nullptr));
+  EXPECT_EQ(ERROR_INVALID_ELF, elf.GetLastErrorCode());
+
   bool finished;
-  ASSERT_FALSE(elf.Step(0, 0, nullptr, nullptr, &finished));
+  ASSERT_FALSE(elf.Step(0, nullptr, nullptr, &finished));
+  EXPECT_EQ(ERROR_INVALID_ELF, elf.GetLastErrorCode());
 }
 
 TEST_F(ElfTest, elf32_invalid_machine) {
@@ -295,9 +299,8 @@
   }
 
   elf.FakeSetValid(true);
-  bool finished;
-  ASSERT_TRUE(elf.Step(0x3000, 0x1000, &regs, &process_memory, &finished));
-  EXPECT_FALSE(finished);
+  ASSERT_TRUE(elf.StepIfSignalHandler(0x3000, &regs, &process_memory));
+  EXPECT_EQ(ERROR_NONE, elf.GetLastErrorCode());
   EXPECT_EQ(15U, regs.pc());
   EXPECT_EQ(13U, regs.sp());
 }
@@ -336,7 +339,7 @@
   EXPECT_CALL(*interface, Step(0x1000, &regs, &process_memory, &finished))
       .WillOnce(::testing::Return(true));
 
-  ASSERT_TRUE(elf.Step(0x1004, 0x1000, &regs, &process_memory, &finished));
+  ASSERT_TRUE(elf.Step(0x1000, &regs, &process_memory, &finished));
 }
 
 TEST_F(ElfTest, get_global_invalid_elf) {