[elf-core] Improve reading memory from core file
This patch tries to improve memory-read from core files
(in order to improve disassembly functionality).
I am using RHEL 7.7 (linux kernel 3.10) and for a lot of cases,
I was not able to disassemble some functions from backtrace when
debugging crashes from core files. It outputs some dummy code.
The cause of the problem was the fact we are returning all the zeros
from ProcessElfCore::ReadMemory() that is being called within
Disassembler::ParseInstructions() and it disassembles some dummy
opcodes from the buffer returned. Therefore, we are removing zero
bytes filling (padding) completely.
Differential Revision: https://reviews.llvm.org/D93939
GitOrigin-RevId: 9abd8c1a4c3870f2831ee805cd3c0cec516a1c17
diff --git a/source/Plugins/Process/elf-core/ProcessElfCore.cpp b/source/Plugins/Process/elf-core/ProcessElfCore.cpp
index ae19367..9896638 100644
--- a/source/Plugins/Process/elf-core/ProcessElfCore.cpp
+++ b/source/Plugins/Process/elf-core/ProcessElfCore.cpp
@@ -353,7 +353,6 @@
const lldb::addr_t file_end = address_range->data.GetRangeEnd();
size_t bytes_to_read = size; // Number of bytes to read from the core file
size_t bytes_copied = 0; // Number of bytes actually read from the core file
- size_t zero_fill_size = 0; // Padding
lldb::addr_t bytes_left =
0; // Number of bytes available in the core file from the given address
@@ -367,24 +366,15 @@
if (file_end > file_start + offset)
bytes_left = file_end - (file_start + offset);
- // Figure out how many bytes we need to zero-fill if we are reading more
- // bytes than available in the on-disk segment
- if (bytes_to_read > bytes_left) {
- zero_fill_size = bytes_to_read - bytes_left;
+ if (bytes_to_read > bytes_left)
bytes_to_read = bytes_left;
- }
// If there is data available on the core file read it
if (bytes_to_read)
bytes_copied =
core_objfile->CopyData(offset + file_start, bytes_to_read, buf);
- assert(zero_fill_size <= size);
- // Pad remaining bytes
- if (zero_fill_size)
- memset(((char *)buf) + bytes_copied, 0, zero_fill_size);
-
- return bytes_copied + zero_fill_size;
+ return bytes_copied;
}
void ProcessElfCore::Clear() {
diff --git a/test/API/functionalities/postmortem/elf-core/TestLinuxCore.py b/test/API/functionalities/postmortem/elf-core/TestLinuxCore.py
index 162503c..f3edf4b 100644
--- a/test/API/functionalities/postmortem/elf-core/TestLinuxCore.py
+++ b/test/API/functionalities/postmortem/elf-core/TestLinuxCore.py
@@ -155,6 +155,24 @@
self.do_test("linux-x86_64", self._x86_64_pid, self._x86_64_regions,
"a.out")
+
+ @skipIf(triple='^mips')
+ @skipIfLLVMTargetMissing("X86")
+ @skipIfWindows
+ @skipIfReproducer
+ def test_read_memory(self):
+ """Test that we are able to read as many bytes as available"""
+ target = self.dbg.CreateTarget("linux-x86_64.out")
+ process = target.LoadCore("linux-x86_64.core")
+ self.assertTrue(process, PROCESS_IS_VALID)
+
+ error = lldb.SBError()
+ bytesread = process.ReadMemory(0x400ff0, 20, error)
+
+ # read only 16 bytes without zero bytes filling
+ self.assertEqual(len(bytesread), 16)
+ self.dbg.DeleteTarget(target)
+
@skipIf(triple='^mips')
@skipIfLLVMTargetMissing("X86")
def test_FPR_SSE(self):
